Merge branch 'develop' of https://github.com/nlohmann/json into update_doctest

2022-03-24 07:55:48 +01:00 · 2022-03-24 07:55:48 +01:00 · 78580ca8bd
commit 78580ca8bd
parent 41754c245a ad103e5b45
47 changed files with 1606 additions and 787 deletions
--- a/.github/workflows/codeql-analysis.yml
+++ b/.github/workflows/codeql-analysis.yml
@ -9,6 +9,7 @@ on:
  pull_request:
  schedule:
    - cron: '0 19 * * 1'
+  workflow_dispatch:

 jobs:
  CodeQL-Build:
--- a/.github/workflows/macos.yml
+++ b/.github/workflows/macos.yml
@ -7,6 +7,7 @@ on:
      - master
      - release/*
  pull_request:
+  workflow_dispatch:

 jobs:
  xcode:
@ -37,7 +38,7 @@ jobs:
    steps:
      - uses: actions/checkout@v2
      - name: cmake
-        run: cmake -S . -B build -D CMAKE_BUILD_TYPE=Debug -DJSON_BuildTests=On -DCMAKE_CXX_STANDARD=${{ matrix.standard }} -DCMAKE_CXX_STANDARD_REQUIRED=ON
+        run: cmake -S . -B build -D CMAKE_BUILD_TYPE=Debug -DJSON_BuildTests=On -DJSON_TestStandards=${{ matrix.standard }}
      - name: build
        run: cmake --build build --parallel 10
      - name: test
--- a/.github/workflows/ubuntu.yml
+++ b/.github/workflows/ubuntu.yml
@ -7,6 +7,7 @@ on:
      - master
      - release/*
  pull_request:
+  workflow_dispatch:

 jobs:
  ci_test_clang:
--- a/.github/workflows/windows.yml
+++ b/.github/workflows/windows.yml
@ -7,6 +7,7 @@ on:
      - master
      - release/*
  pull_request:
+  workflow_dispatch:

 jobs:
  mingw:
@ -64,7 +65,7 @@ jobs:
      run: cd build ; ctest -j 10 -C Release --output-on-failure

  msvc2019:
-    runs-on: windows-latest
+    runs-on: windows-2019
    strategy:
      matrix:
        build_type: [Debug, Release]
@ -84,7 +85,7 @@ jobs:
      run: cd build ; ctest -j 10 -C ${{ matrix.build_type }} --output-on-failure

  msvc2019_latest:
-    runs-on: windows-latest
+    runs-on: windows-2019

    steps:
    - uses: actions/checkout@v2
@ -95,8 +96,40 @@ jobs:
    - name: test
      run: cd build ; ctest -j 10 -C Release --output-on-failure

+  msvc2022:
+    runs-on: windows-2022
+    strategy:
+      matrix:
+        build_type: [Debug, Release]
+        architecture: [Win32, x64]
+
+    steps:
+    - uses: actions/checkout@v2
+    - name: cmake
+      run: cmake -S . -B build -G "Visual Studio 17 2022" -A ${{ matrix.architecture }} -DJSON_BuildTests=On -DCMAKE_CXX_FLAGS="/W4 /WX"
+      if: matrix.build_type == 'Release'
+    - name: cmake
+      run: cmake -S . -B build -G "Visual Studio 17 2022" -A ${{ matrix.architecture }} -DJSON_BuildTests=On -DJSON_FastTests=ON -DCMAKE_CXX_FLAGS="/W4 /WX"
+      if: matrix.build_type == 'Debug'
+    - name: build
+      run: cmake --build build --config ${{ matrix.build_type }} --parallel 10
+    - name: test
+      run: cd build ; ctest -j 10 -C ${{ matrix.build_type }} --output-on-failure
+
+  msvc2022_latest:
+    runs-on: windows-2022
+
+    steps:
+    - uses: actions/checkout@v2
+    - name: cmake
+      run: cmake -S . -B build -G "Visual Studio 17 2022" -DJSON_BuildTests=On -DCMAKE_CXX_FLAGS="/permissive- /std:c++latest /utf-8 /W4 /WX"
+    - name: build
+      run: cmake --build build --config Release --parallel 10
+    - name: test
+      run: cd build ; ctest -j 10 -C Release --output-on-failure
+
  clang:
-    runs-on: windows-latest
+    runs-on: windows-2019
    strategy:
      matrix:
        version: [11, 12]
@ -113,7 +146,7 @@ jobs:
        run: cd build ; ctest -j 10 -C Debug --exclude-regex "test-unicode" --output-on-failure

  clang-cl-11:
-    runs-on: windows-latest
+    runs-on: windows-2019
    strategy:
      matrix:
        architecture: [Win32, x64]
--- a/CITATION.cff
+++ b/CITATION.cff
@ -1,6 +1,6 @@
-cff-version: 1.1.0
+cff-version: 1.2.0
 message: "If you use this software, please cite it as below."
-authors: 
+authors:
  - family-names: Lohmann
    given-names: Niels
    orcid: https://orcid.org/0000-0001-9037-795X
@ -8,7 +8,7 @@ authors:
    website: https://nlohmann.me
 title: "JSON for Modern C++"
 version: 3.10.5
-date-released: 2022
+date-released: 2022-01-03
 license: MIT
 repository-code: "https://github.com/nlohmann"
 url: https://json.nlohmann.me
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@ -19,6 +19,7 @@ endif()
 ## INCLUDE
 ##
 ##
+set(CMAKE_MODULE_PATH ${CMAKE_CURRENT_SOURCE_DIR}/cmake ${CMAKE_MODULE_PATH})
 include(ExternalProject)

 ##
@ -30,7 +31,13 @@ if (POLICY CMP0077)
    cmake_policy(SET CMP0077 NEW)
 endif ()

-option(JSON_BuildTests          "Build the unit tests when BUILD_TESTING is enabled." ${MAIN_PROJECT})
+# VERSION_GREATER_EQUAL is not available in CMake 3.1
+if(${MAIN_PROJECT} AND (${CMAKE_VERSION} VERSION_EQUAL 3.13 OR ${CMAKE_VERSION} VERSION_GREATER 3.13))
+    set(JSON_BuildTests_INIT ON)
+else()
+    set(JSON_BuildTests_INIT OFF)
+endif()
+option(JSON_BuildTests          "Build the unit tests when BUILD_TESTING is enabled." ${JSON_BuildTests_INIT})
 option(JSON_CI                  "Enable CI build targets." OFF)
 option(JSON_Diagnostics         "Use extended diagnostic messages." OFF)
 option(JSON_ImplicitConversions "Enable implicit conversions." ON)
@ -39,7 +46,7 @@ option(JSON_MultipleHeaders     "Use non-amalgamated version of the library." OF
 option(JSON_SystemInclude       "Include as system headers (skip for clang-tidy)." OFF)

 if (JSON_CI)
-    include(cmake/ci.cmake)
+    include(ci)
 endif ()

 ##
--- a/36
+++ b/36
@ -4,9 +4,6 @@
 # configuration
 ##########################################################################

-# directory to recent compiler binaries
-COMPILER_DIR=/usr/local/opt/llvm/bin
-
 # find GNU sed to use `-i` parameter
 SED:=$(shell command -v gsed || which sed)

@ -62,6 +59,7 @@ run_benchmarks:
 	cd cmake-build-benchmarks ; ninja
 	cd cmake-build-benchmarks ; ./json_benchmarks

+
 ##########################################################################
 # fuzzing
 ##########################################################################
@ -135,6 +133,7 @@ pvs_studio:
 	cd cmake-build-pvs-studio ; plog-converter -a'GA:1,2;64:1;CS' -t fullhtml PVS-Studio.log -o pvs
 	open cmake-build-pvs-studio/pvs/index.html

+
 ##########################################################################
 # Code format and source amalgamation
 ##########################################################################
@ -203,20 +202,29 @@ ChangeLog.md:
 # Release files
 ##########################################################################

-# Create the files for a release and add signatures and hashes. We use `-X` to make the resulting ZIP file
-# reproducible, see <https://content.pivotal.io/blog/barriers-to-deterministic-reproducible-zip-files>.
+# Create a tar.gz archive that contains sufficient files to be used as CMake project (e.g., using FetchContent). The
+# archive is created according to the advices of <https://reproducible-builds.org/docs/archives/>.
+json.tar.xz:
+	mkdir json
+	rsync -R $(shell find LICENSE.MIT nlohmann_json.natvis CMakeLists.txt cmake/*.in include single_include -type f) json
+	gtar --sort=name --mtime="@$(shell git log -1 --pretty=%ct)" --owner=0 --group=0 --numeric-owner --pax-option=exthdr.name=%d/PaxHeaders/%f,delete=atime,delete=ctime --create --file - json | xz --compress -9e --threads=2 - > json.tar.xz
+	rm -fr json

-release:
+# We use `-X` to make the resulting ZIP file reproducible, see
+# <https://content.pivotal.io/blog/barriers-to-deterministic-reproducible-zip-files>.
+include.zip:
+	zip -9 --recurse-paths -X include.zip $(SRCS) $(AMALGAMATED_FILE) meson.build LICENSE.MIT
+
+# Create the files for a release and add signatures and hashes.
+release: include.zip json.tar.xz
 	rm -fr release_files
 	mkdir release_files
-	zip -9 --recurse-paths -X include.zip $(SRCS) $(AMALGAMATED_FILE) meson.build LICENSE.MIT
 	gpg --armor --detach-sig include.zip
-	mv include.zip include.zip.asc release_files
 	gpg --armor --detach-sig $(AMALGAMATED_FILE)
+	gpg --armor --detach-sig json.tar.xz
 	cp $(AMALGAMATED_FILE) release_files
-	mv $(AMALGAMATED_FILE).asc release_files
-	cd release_files ; shasum -a 256 json.hpp > hashes.txt
-	cd release_files ; shasum -a 256 include.zip >> hashes.txt
+	mv $(AMALGAMATED_FILE).asc json.tar.xz json.tar.xz.asc include.zip include.zip.asc release_files
+	cd release_files ; shasum -a 256 json.hpp include.zip json.tar.xz > hashes.txt


 ##########################################################################
@ -225,12 +233,12 @@ release:

 # clean up
 clean:
-	rm -fr json_unit json_benchmarks fuzz fuzz-testing *.dSYM test/*.dSYM oclint_report.html
+	rm -fr fuzz fuzz-testing *.dSYM test/*.dSYM
 	rm -fr benchmarks/files/numbers/*.json
-	rm -fr cmake-3.1.0-Darwin64.tar.gz cmake-3.1.0-Darwin64
-	rm -fr cmake-build-benchmarks cmake-build-pedantic fuzz-testing cmake-build-clang-analyze cmake-build-pvs-studio cmake-build-infer cmake_build
+	rm -fr cmake-build-benchmarks fuzz-testing cmake-build-pvs-studio release_files
 	$(MAKE) clean -Cdoc

+
 ##########################################################################
 # Thirdparty code
 ##########################################################################
--- a/README.md
+++ b/README.md
@ -10,7 +10,7 @@
 [![Language grade: C/C++](https://img.shields.io/lgtm/grade/cpp/g/nlohmann/json.svg?logo=lgtm&logoWidth=18)](https://lgtm.com/projects/g/nlohmann/json/context:cpp)
 [![Fuzzing Status](https://oss-fuzz-build-logs.storage.googleapis.com/badges/json.svg)](https://bugs.chromium.org/p/oss-fuzz/issues/list?sort=-opened&can=1&q=proj:json)
 [![Try online](https://img.shields.io/badge/try-online-blue.svg)](https://wandbox.org/permlink/1mp10JbaANo6FUc7)
-[![Documentation](https://img.shields.io/badge/docs-doxygen-blue.svg)](https://nlohmann.github.io/json/doxygen/index.html)
+[![Documentation](https://img.shields.io/badge/docs-mkdocs-blue.svg)](https://json.nlohmann.me)
 [![GitHub license](https://img.shields.io/badge/license-MIT-blue.svg)](https://raw.githubusercontent.com/nlohmann/json/master/LICENSE.MIT)
 [![GitHub Releases](https://img.shields.io/github/release/nlohmann/json.svg)](https://github.com/nlohmann/json/releases)
 [![GitHub Downloads](https://img.shields.io/github/downloads/nlohmann/json/total)](https://github.com/nlohmann/json/releases)
@ -85,7 +85,7 @@ Thanks everyone!

 :books: If you want to **learn more** about how to use the library, check out the rest of the [**README**](#examples), have a look at [**code examples**](https://github.com/nlohmann/json/tree/develop/doc/examples), or browse through the [**help pages**](https://json.nlohmann.me).

-:construction: If you want to understand the **API** better, check out the [**API Reference**](https://json.nlohmann.me/api/basic_json/) or the [**Doxygen documentation**](https://json.nlohmann.me/doxygen/index.html).
+:construction: If you want to understand the **API** better, check out the [**API Reference**](https://json.nlohmann.me/api/basic_json/).

 :bug: If you found a **bug**, please check the [**FAQ**](https://json.nlohmann.me/home/faq/) if it is a known issue or the result of a design decision. Please also have a look at the [**issue list**](https://github.com/nlohmann/json/issues) before you [**create a new issue**](https://github.com/nlohmann/json/issues/new/choose). Please provide as much information as possible to help us understand and reproduce your issue.

@ -1045,6 +1045,7 @@ Though it's 2022 already, the support for C++11 is still a bit sparse. Currently
 - Microsoft Visual C++ 2015 / Build Tools 14.0.25123.0 (and possibly later)
 - Microsoft Visual C++ 2017 / Build Tools 15.5.180.51428 (and possibly later)
 - Microsoft Visual C++ 2019 / Build Tools 16.3.1+1def00d3d (and possibly later)
+- Microsoft Visual C++ 2022 / Build Tools 19.30.30709.0 (and possibly later)

 I would be happy to learn about other compilers/versions.

@ -1119,6 +1120,7 @@ The following compilers are currently used in continuous integration at [AppVeyo
 | Visual Studio 15 2017 MSVC 19.16.27045.0 (Build Engine version 15.9.21+g9802d43bc3 for .NET Framework) | Windows-10.0.14393 | GitHub Actions |
 | Visual Studio 16 2019 MSVC 19.28.29912.0 (Build Engine version 16.9.0+57a23d249 for .NET Framework)    | Windows-10.0.17763 | GitHub Actions |
 | Visual Studio 16 2019 MSVC 19.28.29912.0 (Build Engine version 16.9.0+57a23d249 for .NET Framework)    | Windows-10.0.17763 | AppVeyor       |
+| Visual Studio 17 2022 MSVC 19.30.30709.0 (Build Engine version 17.0.31804.368 for .NET Framework)      | Windows-10.0.20348 | GitHub Actions |


 ## Integration
@ -1183,29 +1185,20 @@ target_link_libraries(foo PRIVATE nlohmann_json::nlohmann_json)

 Since CMake v3.11,
 [FetchContent](https://cmake.org/cmake/help/v3.11/module/FetchContent.html) can
-be used to automatically download the repository as a dependency at configure time.
+be used to automatically download a release as a dependency at configure time.

 Example:
 ```cmake
 include(FetchContent)

-FetchContent_Declare(json
-  GIT_REPOSITORY https://github.com/nlohmann/json.git
-  GIT_TAG v3.7.3)
-
-FetchContent_GetProperties(json)
-if(NOT json_POPULATED)
-  FetchContent_Populate(json)
-  add_subdirectory(${json_SOURCE_DIR} ${json_BINARY_DIR} EXCLUDE_FROM_ALL)
-endif()
+FetchContent_Declare(json URL https://github.com/nlohmann/json/releases/download/v3.10.5/json.tar.xz)
+FetchContent_MakeAvailable(json)

 target_link_libraries(foo PRIVATE nlohmann_json::nlohmann_json)
 ```

-**Note**: The repository https://github.com/nlohmann/json download size is huge.
-It contains all the dataset used for the benchmarks. You might want to depend on
-a smaller repository. For instance, you might want to replace the URL above by
-https://github.com/ArthurSonzogni/nlohmann_json_cmake_fetchcontent
+**Note**: It is recommended to use the URL approach described above which is supported as of version 3.10.0. See
+<https://json.nlohmann.me/integration/cmake/#fetchcontent> for more information.

 #### Supporting Both

@ -1624,13 +1617,14 @@ The library itself consists of a single header file licensed under the MIT licen
 - [**Coverity Scan**](https://scan.coverity.com) for [static analysis](https://scan.coverity.com/projects/nlohmann-json)
 - [**cppcheck**](http://cppcheck.sourceforge.net) for static analysis
 - [**doctest**](https://github.com/onqtam/doctest) for the unit tests
- [**Doxygen**](https://www.doxygen.nl/index.html) to generate [documentation](https://nlohmann.github.io/json/doxygen/index.html)
 - [**git-update-ghpages**](https://github.com/rstacruz/git-update-ghpages) to upload the documentation to gh-pages
 - [**GitHub Changelog Generator**](https://github.com/skywinder/github-changelog-generator) to generate the [ChangeLog](https://github.com/nlohmann/json/blob/develop/ChangeLog.md)
 - [**Google Benchmark**](https://github.com/google/benchmark) to implement the benchmarks
 - [**Hedley**](https://nemequ.github.io/hedley/) to avoid re-inventing several compiler-agnostic feature macros
 - [**lcov**](http://ltp.sourceforge.net/coverage/lcov.php) to process coverage information and create an HTML view
 - [**libFuzzer**](https://llvm.org/docs/LibFuzzer.html) to implement fuzz testing for OSS-Fuzz
+- [**Material for MkDocs**](https://squidfunk.github.io/mkdocs-material/) for the style of the documentation site
+- [**MkDocs**](https://www.mkdocs.org) for the documentation site
 - [**OSS-Fuzz**](https://github.com/google/oss-fuzz) for continuous fuzz testing of the library ([project repository](https://github.com/google/oss-fuzz/tree/master/projects/json))
 - [**Probot**](https://probot.github.io) for automating maintainer tasks such as closing stale issues, requesting missing information, or detecting toxic comments.
 - [**Valgrind**](https://valgrind.org) to check for correct memory management
--- a/benchmarks/CMakeLists.txt
+++ b/benchmarks/CMakeLists.txt
@ -23,7 +23,7 @@ if(NOT benchmark_POPULATED)
 endif()

 # download test data
-include(${CMAKE_SOURCE_DIR}/../cmake/download_test_data.cmake)
+include(download_test_data)

 # benchmark binary
 add_executable(json_benchmarks src/benchmarks.cpp)
--- a/cmake/ci.cmake
+++ b/cmake/ci.cmake
@ -30,7 +30,7 @@ execute_process(COMMAND ${CPPCHECK_TOOL} --version OUTPUT_VARIABLE CPPCHECK_TOOL
 string(REGEX MATCH "[0-9]+(\\.[0-9]+)+" CPPCHECK_TOOL_VERSION "${CPPCHECK_TOOL_VERSION}")
 message(STATUS "🔖 Cppcheck ${CPPCHECK_TOOL_VERSION} (${CPPCHECK_TOOL})")

-find_program(GCC_TOOL NAMES g++-HEAD g++-11 g++-latest)
+find_program(GCC_TOOL NAMES g++-latest g++-HEAD g++-11)
 execute_process(COMMAND ${GCC_TOOL} --version OUTPUT_VARIABLE GCC_TOOL_VERSION ERROR_VARIABLE GCC_TOOL_VERSION)
 string(REGEX MATCH "[0-9]+(\\.[0-9]+)+" GCC_TOOL_VERSION "${GCC_TOOL_VERSION}")
 message(STATUS "🔖 GCC ${GCC_TOOL_VERSION} (${GCC_TOOL})")
@ -98,19 +98,20 @@ file(GLOB_RECURSE SRC_FILES ${PROJECT_SOURCE_DIR}/include/nlohmann/*.hpp)
 # -Wno-weak-vtables               The library is header-only.
 # -Wreserved-identifier           See https://github.com/onqtam/doctest/issues/536.

-set(CLANG_CXXFLAGS "-std=c++11                        \
-    -Werror                                           \
-    -Weverything                                      \
-    -Wno-c++98-compat                                    \
-    -Wno-c++98-compat-pedantic                           \
-    -Wno-deprecated-declarations                         \
-    -Wno-extra-semi-stmt                                 \
-    -Wno-padded                                          \
-    -Wno-covered-switch-default                          \
-    -Wno-weak-vtables                                    \
-    -Wno-reserved-identifier                             \
-")
+set(CLANG_CXXFLAGS
+    -Werror
+    -Weverything
+    -Wno-c++98-compat
+    -Wno-c++98-compat-pedantic
+    -Wno-deprecated-declarations
+    -Wno-extra-semi-stmt
+    -Wno-padded
+    -Wno-covered-switch-default
+    -Wno-weak-vtables
+    -Wno-reserved-identifier
+)

+# Warning flags determined for GCC 12.0 (experimental) with https://github.com/nlohmann/gcc_flags:
 # Ignored GCC warnings:
 # -Wno-abi-tag                    We do not care about ABI tags.
 # -Wno-aggregate-return           The library uses aggregate returns.
@ -120,283 +121,295 @@ set(CLANG_CXXFLAGS "-std=c++11                        \
 # -Wno-system-headers             We do not care about warnings in system headers.
 # -Wno-templates                  The library uses templates.

-set(GCC_CXXFLAGS "-std=c++11                          \
-    -pedantic                                         \
-    -Werror                                           \
-    --all-warnings                                    \
-    --extra-warnings                                  \
-    -W                                                \
-    -WNSObject-attribute                              \
-    -Wno-abi-tag                                         \
-    -Waddress                                         \
-    -Waddress-of-packed-member                        \
-    -Wno-aggregate-return                                \
-    -Waggressive-loop-optimizations                   \
-    -Waligned-new=all                                 \
-    -Wall                                             \
-    -Walloc-zero                                      \
-    -Walloca                                          \
-    -Wanalyzer-double-fclose                          \
-    -Wanalyzer-double-free                            \
-    -Wanalyzer-exposure-through-output-file           \
-    -Wanalyzer-file-leak                              \
-    -Wanalyzer-free-of-non-heap                       \
-    -Wanalyzer-malloc-leak                            \
-    -Wanalyzer-mismatching-deallocation               \
-    -Wanalyzer-null-argument                          \
-    -Wanalyzer-null-dereference                       \
-    -Wanalyzer-possible-null-argument                 \
-    -Wanalyzer-possible-null-dereference              \
-    -Wanalyzer-shift-count-negative                   \
-    -Wanalyzer-shift-count-overflow                   \
-    -Wanalyzer-stale-setjmp-buffer                    \
-    -Wanalyzer-tainted-array-index                    \
-    -Wanalyzer-too-complex                            \
-    -Wanalyzer-unsafe-call-within-signal-handler      \
-    -Wanalyzer-use-after-free                         \
-    -Wanalyzer-use-of-pointer-in-stale-stack-frame    \
-    -Wanalyzer-write-to-const                         \
-    -Wanalyzer-write-to-string-literal                \
-    -Warith-conversion                                \
-    -Warray-bounds                                    \
-    -Warray-bounds=2                                  \
-    -Warray-parameter=2                               \
-    -Wattribute-alias=2                               \
-    -Wattribute-warning                               \
-    -Wattributes                                      \
-    -Wbool-compare                                    \
-    -Wbool-operation                                  \
-    -Wbuiltin-declaration-mismatch                    \
-    -Wbuiltin-macro-redefined                         \
-    -Wc++0x-compat                                    \
-    -Wc++11-compat                                    \
-    -Wc++14-compat                                    \
-    -Wc++17-compat                                    \
-    -Wc++1z-compat                                    \
-    -Wc++20-compat                                    \
-    -Wc++2a-compat                                    \
-    -Wcannot-profile                                  \
-    -Wcast-align                                      \
-    -Wcast-align=strict                               \
-    -Wcast-function-type                              \
-    -Wcast-qual                                       \
-    -Wcatch-value=3                                   \
-    -Wchar-subscripts                                 \
-    -Wclass-conversion                                \
-    -Wclass-memaccess                                 \
-    -Wclobbered                                       \
-    -Wcomma-subscript                                 \
-    -Wcomment                                         \
-    -Wcomments                                        \
-    -Wconditionally-supported                         \
-    -Wconversion                                      \
-    -Wconversion-null                                 \
-    -Wcoverage-mismatch                               \
-    -Wcpp                                             \
-    -Wctad-maybe-unsupported                          \
-    -Wctor-dtor-privacy                               \
-    -Wdangling-else                                   \
-    -Wdate-time                                       \
-    -Wdelete-incomplete                               \
-    -Wdelete-non-virtual-dtor                         \
-    -Wdeprecated                                      \
-    -Wdeprecated-copy                                 \
-    -Wdeprecated-copy-dtor                            \
-    -Wdeprecated-declarations                         \
-    -Wdeprecated-enum-enum-conversion                 \
-    -Wdeprecated-enum-float-conversion                \
-    -Wdisabled-optimization                           \
-    -Wdiv-by-zero                                     \
-    -Wdouble-promotion                                \
-    -Wduplicated-branches                             \
-    -Wduplicated-cond                                 \
-    -Weffc++                                          \
-    -Wempty-body                                      \
-    -Wendif-labels                                    \
-    -Wenum-compare                                    \
-    -Wenum-conversion                                 \
-    -Wexpansion-to-defined                            \
-    -Wextra                                           \
-    -Wextra-semi                                      \
-    -Wfloat-conversion                                \
-    -Wfloat-equal                                     \
-    -Wformat-contains-nul                             \
-    -Wformat-diag                                     \
-    -Wformat-extra-args                               \
-    -Wformat-nonliteral                               \
-    -Wformat-overflow=2                               \
-    -Wformat-security                                 \
-    -Wformat-signedness                               \
-    -Wformat-truncation=2                             \
-    -Wformat-y2k                                      \
-    -Wformat-zero-length                              \
-    -Wformat=2                                        \
-    -Wframe-address                                   \
-    -Wfree-nonheap-object                             \
-    -Whsa                                             \
-    -Wif-not-aligned                                  \
-    -Wignored-attributes                              \
-    -Wignored-qualifiers                              \
-    -Wimplicit-fallthrough=5                          \
-    -Winaccessible-base                               \
-    -Winherited-variadic-ctor                         \
-    -Winit-list-lifetime                              \
-    -Winit-self                                       \
-    -Winline                                          \
-    -Wint-in-bool-context                             \
-    -Wint-to-pointer-cast                             \
-    -Winvalid-memory-model                            \
-    -Winvalid-offsetof                                \
-    -Winvalid-pch                                     \
-    -Wliteral-suffix                                  \
-    -Wlogical-not-parentheses                         \
-    -Wlogical-op                                      \
-    -Wno-long-long                                       \
-    -Wlto-type-mismatch                               \
-    -Wmain                                            \
-    -Wmaybe-uninitialized                             \
-    -Wmemset-elt-size                                 \
-    -Wmemset-transposed-args                          \
-    -Wmisleading-indentation                          \
-    -Wmismatched-dealloc                              \
-    -Wmismatched-new-delete                           \
-    -Wmismatched-tags                                 \
-    -Wmissing-attributes                              \
-    -Wmissing-braces                                  \
-    -Wmissing-declarations                            \
-    -Wmissing-field-initializers                      \
-    -Wmissing-include-dirs                            \
-    -Wmissing-profile                                 \
-    -Wmultichar                                       \
-    -Wmultiple-inheritance                            \
-    -Wmultistatement-macros                           \
-    -Wno-namespaces                                      \
-    -Wnarrowing                                       \
-    -Wnoexcept                                        \
-    -Wnoexcept-type                                   \
-    -Wnon-template-friend                             \
-    -Wnon-virtual-dtor                                \
-    -Wnonnull                                         \
-    -Wnonnull-compare                                 \
-    -Wnormalized=nfkc                                 \
-    -Wnull-dereference                                \
-    -Wodr                                             \
-    -Wold-style-cast                                  \
-    -Wopenmp-simd                                     \
-    -Woverflow                                        \
-    -Woverlength-strings                              \
-    -Woverloaded-virtual                              \
-    -Wpacked                                          \
-    -Wpacked-bitfield-compat                          \
-    -Wpacked-not-aligned                              \
-    -Wno-padded                                          \
-    -Wparentheses                                     \
-    -Wpedantic                                        \
-    -Wpessimizing-move                                \
-    -Wplacement-new=2                                 \
-    -Wpmf-conversions                                 \
-    -Wpointer-arith                                   \
-    -Wpointer-compare                                 \
-    -Wpragmas                                         \
-    -Wprio-ctor-dtor                                  \
-    -Wpsabi                                           \
-    -Wrange-loop-construct                            \
-    -Wredundant-decls                                 \
-    -Wredundant-move                                  \
-    -Wredundant-tags                                  \
-    -Wregister                                        \
-    -Wreorder                                         \
-    -Wrestrict                                        \
-    -Wreturn-local-addr                               \
-    -Wreturn-type                                     \
-    -Wscalar-storage-order                            \
-    -Wsequence-point                                  \
-    -Wshadow=compatible-local                         \
-    -Wshadow=global                                   \
-    -Wshadow=local                                    \
-    -Wshift-count-negative                            \
-    -Wshift-count-overflow                            \
-    -Wshift-negative-value                            \
-    -Wshift-overflow=2                                \
-    -Wsign-compare                                    \
-    -Wsign-conversion                                 \
-    -Wsign-promo                                      \
-    -Wsized-deallocation                              \
-    -Wsizeof-array-argument                           \
-    -Wsizeof-array-div                                \
-    -Wsizeof-pointer-div                              \
-    -Wsizeof-pointer-memaccess                        \
-    -Wstack-protector                                 \
-    -Wstrict-aliasing                                 \
-    -Wstrict-aliasing=3                               \
-    -Wstrict-null-sentinel                            \
-    -Wstrict-overflow                                 \
-    -Wstrict-overflow=5                               \
-    -Wstring-compare                                  \
-    -Wstringop-overflow=4                             \
-    -Wstringop-overread                               \
-    -Wstringop-truncation                             \
-    -Wsubobject-linkage                               \
-    -Wsuggest-attribute=cold                          \
-    -Wsuggest-attribute=const                         \
-    -Wsuggest-attribute=format                        \
-    -Wsuggest-attribute=malloc                        \
-    -Wsuggest-attribute=noreturn                      \
-    -Wsuggest-attribute=pure                          \
-    -Wsuggest-final-methods                           \
-    -Wsuggest-final-types                             \
-    -Wsuggest-override                                \
-    -Wswitch                                          \
-    -Wswitch-bool                                     \
-    -Wswitch-default                                  \
-    -Wswitch-enum                                     \
-    -Wswitch-outside-range                            \
-    -Wswitch-unreachable                              \
-    -Wsync-nand                                       \
-    -Wsynth                                           \
-    -Wno-system-headers                                  \
-    -Wtautological-compare                            \
-    -Wno-templates                                       \
-    -Wterminate                                       \
-    -Wtrampolines                                     \
-    -Wtrigraphs                                       \
-    -Wtsan                                            \
-    -Wtype-limits                                     \
-    -Wundef                                           \
-    -Wuninitialized                                   \
-    -Wunknown-pragmas                                 \
-    -Wunreachable-code                                \
-    -Wunsafe-loop-optimizations                       \
-    -Wunused                                          \
-    -Wunused-but-set-parameter                        \
-    -Wunused-but-set-variable                         \
-    -Wunused-const-variable=2                         \
-    -Wunused-function                                 \
-    -Wunused-label                                    \
-    -Wunused-local-typedefs                           \
-    -Wunused-macros                                   \
-    -Wunused-parameter                                \
-    -Wunused-result                                   \
-    -Wunused-value                                    \
-    -Wunused-variable                                 \
-    -Wuseless-cast                                    \
-    -Wvarargs                                         \
-    -Wvariadic-macros                                 \
-    -Wvector-operation-performance                    \
-    -Wvexing-parse                                    \
-    -Wvirtual-inheritance                             \
-    -Wvirtual-move-assign                             \
-    -Wvla                                             \
-    -Wvla-parameter                                   \
-    -Wvolatile                                        \
-    -Wvolatile-register-var                           \
-    -Wwrite-strings                                   \
-    -Wzero-as-null-pointer-constant                   \
-    -Wzero-length-bounds                              \
-")
+set(GCC_CXXFLAGS
+    -pedantic
+    -Werror
+    --all-warnings
+    --extra-warnings
+    -W
+    -WNSObject-attribute
+    -Wno-abi-tag
+    -Waddress
+    -Waddress-of-packed-member
+    -Wno-aggregate-return
+    -Waggressive-loop-optimizations
+    -Waligned-new=all
+    -Wall
+    -Walloc-zero
+    -Walloca
+    -Wanalyzer-double-fclose
+    -Wanalyzer-double-free
+    -Wanalyzer-exposure-through-output-file
+    -Wanalyzer-file-leak
+    -Wanalyzer-free-of-non-heap
+    -Wanalyzer-malloc-leak
+    -Wanalyzer-mismatching-deallocation
+    -Wanalyzer-null-argument
+    -Wanalyzer-null-dereference
+    -Wanalyzer-possible-null-argument
+    -Wanalyzer-possible-null-dereference
+    -Wanalyzer-shift-count-negative
+    -Wanalyzer-shift-count-overflow
+    -Wanalyzer-stale-setjmp-buffer
+    -Wanalyzer-tainted-allocation-size
+    -Wanalyzer-tainted-array-index
+    -Wanalyzer-tainted-divisor
+    -Wanalyzer-tainted-offset
+    -Wanalyzer-tainted-size
+    -Wanalyzer-too-complex
+    -Wanalyzer-unsafe-call-within-signal-handler
+    -Wanalyzer-use-after-free
+    -Wanalyzer-use-of-pointer-in-stale-stack-frame
+    -Wanalyzer-use-of-uninitialized-value
+    -Wanalyzer-write-to-const
+    -Wanalyzer-write-to-string-literal
+    -Warith-conversion
+    -Warray-bounds
+    -Warray-bounds=2
+    -Warray-compare
+    -Warray-parameter=2
+    -Wattribute-alias=2
+    -Wattribute-warning
+    -Wattributes
+    -Wbool-compare
+    -Wbool-operation
+    -Wbuiltin-declaration-mismatch
+    -Wbuiltin-macro-redefined
+    -Wc++0x-compat
+    -Wc++11-compat
+    -Wc++11-extensions
+    -Wc++14-compat
+    -Wc++14-extensions
+    -Wc++17-compat
+    -Wc++17-extensions
+    -Wc++1z-compat
+    -Wc++20-compat
+    -Wc++20-extensions
+    -Wc++23-extensions
+    -Wc++2a-compat
+    -Wcannot-profile
+    -Wcast-align
+    -Wcast-align=strict
+    -Wcast-function-type
+    -Wcast-qual
+    -Wcatch-value=3
+    -Wchar-subscripts
+    -Wclass-conversion
+    -Wclass-memaccess
+    -Wclobbered
+    -Wcomma-subscript
+    -Wcomment
+    -Wcomments
+    -Wconditionally-supported
+    -Wconversion
+    -Wconversion-null
+    -Wcoverage-invalid-line-number
+    -Wcoverage-mismatch
+    -Wcpp
+    -Wctad-maybe-unsupported
+    -Wctor-dtor-privacy
+    -Wdangling-else
+    -Wdate-time
+    -Wdelete-incomplete
+    -Wdelete-non-virtual-dtor
+    -Wdeprecated
+    -Wdeprecated-copy
+    -Wdeprecated-copy-dtor
+    -Wdeprecated-declarations
+    -Wdeprecated-enum-enum-conversion
+    -Wdeprecated-enum-float-conversion
+    -Wdisabled-optimization
+    -Wdiv-by-zero
+    -Wdouble-promotion
+    -Wduplicated-branches
+    -Wduplicated-cond
+    -Weffc++
+    -Wempty-body
+    -Wendif-labels
+    -Wenum-compare
+    -Wenum-conversion
+    -Wexceptions
+    -Wexpansion-to-defined
+    -Wextra
+    -Wextra-semi
+    -Wfloat-conversion
+    -Wfloat-equal
+    -Wformat-diag
+    -Wformat-overflow=2
+    -Wformat-signedness
+    -Wformat-truncation=2
+    -Wformat=2
+    -Wframe-address
+    -Wfree-nonheap-object
+    -Whsa
+    -Wif-not-aligned
+    -Wignored-attributes
+    -Wignored-qualifiers
+    -Wimplicit-fallthrough=5
+    -Winaccessible-base
+    -Winfinite-recursion
+    -Winherited-variadic-ctor
+    -Winit-list-lifetime
+    -Winit-self
+    -Winline
+    -Wint-in-bool-context
+    -Wint-to-pointer-cast
+    -Winterference-size
+    -Winvalid-imported-macros
+    -Winvalid-memory-model
+    -Winvalid-offsetof
+    -Winvalid-pch
+    -Wliteral-suffix
+    -Wlogical-not-parentheses
+    -Wlogical-op
+    -Wno-long-long
+    -Wlto-type-mismatch
+    -Wmain
+    -Wmaybe-uninitialized
+    -Wmemset-elt-size
+    -Wmemset-transposed-args
+    -Wmisleading-indentation
+    -Wmismatched-dealloc
+    -Wmismatched-new-delete
+    -Wmismatched-tags
+    -Wmissing-attributes
+    -Wmissing-braces
+    -Wmissing-declarations
+    -Wmissing-field-initializers
+    -Wmissing-include-dirs
+    -Wmissing-profile
+    -Wmissing-requires
+    -Wmultichar
+    -Wmultiple-inheritance
+    -Wmultistatement-macros
+    -Wno-namespaces
+    -Wnarrowing
+    -Wnoexcept
+    -Wnoexcept-type
+    -Wnon-template-friend
+    -Wnon-virtual-dtor
+    -Wnonnull
+    -Wnonnull-compare
+    -Wnormalized=nfkc
+    -Wnull-dereference
+    -Wodr
+    -Wold-style-cast
+    -Wopenacc-parallelism
+    -Wopenmp-simd
+    -Woverflow
+    -Woverlength-strings
+    -Woverloaded-virtual
+    -Wpacked
+    -Wpacked-bitfield-compat
+    -Wpacked-not-aligned
+    -Wno-padded
+    -Wparentheses
+    -Wpedantic
+    -Wpessimizing-move
+    -Wplacement-new=2
+    -Wpmf-conversions
+    -Wpointer-arith
+    -Wpointer-compare
+    -Wpragmas
+    -Wprio-ctor-dtor
+    -Wpsabi
+    -Wrange-loop-construct
+    -Wredundant-decls
+    -Wredundant-move
+    -Wredundant-tags
+    -Wregister
+    -Wreorder
+    -Wrestrict
+    -Wreturn-local-addr
+    -Wreturn-type
+    -Wscalar-storage-order
+    -Wsequence-point
+    -Wshadow=compatible-local
+    -Wshadow=global
+    -Wshadow=local
+    -Wshift-count-negative
+    -Wshift-count-overflow
+    -Wshift-negative-value
+    -Wshift-overflow=2
+    -Wsign-compare
+    -Wsign-conversion
+    -Wsign-promo
+    -Wsized-deallocation
+    -Wsizeof-array-argument
+    -Wsizeof-array-div
+    -Wsizeof-pointer-div
+    -Wsizeof-pointer-memaccess
+    -Wstack-protector
+    -Wstrict-aliasing
+    -Wstrict-aliasing=3
+    -Wstrict-null-sentinel
+    -Wstrict-overflow
+    -Wstrict-overflow=5
+    -Wstring-compare
+    -Wstringop-overflow=4
+    -Wstringop-overread
+    -Wstringop-truncation
+    -Wsubobject-linkage
+    -Wsuggest-attribute=cold
+    -Wsuggest-attribute=const
+    -Wsuggest-attribute=format
+    -Wsuggest-attribute=malloc
+    -Wsuggest-attribute=noreturn
+    -Wsuggest-attribute=pure
+    -Wsuggest-final-methods
+    -Wsuggest-final-types
+    -Wsuggest-override
+    -Wswitch
+    -Wswitch-bool
+    -Wswitch-default
+    -Wswitch-enum
+    -Wswitch-outside-range
+    -Wswitch-unreachable
+    -Wsync-nand
+    -Wsynth
+    -Wno-system-headers
+    -Wtautological-compare
+    -Wno-templates
+    -Wterminate
+    -Wtrampolines
+    -Wtrigraphs
+    -Wtsan
+    -Wtype-limits
+    -Wundef
+    -Wuninitialized
+    -Wunknown-pragmas
+    -Wunreachable-code
+    -Wunsafe-loop-optimizations
+    -Wunused
+    -Wunused-but-set-parameter
+    -Wunused-but-set-variable
+    -Wunused-const-variable=2
+    -Wunused-function
+    -Wunused-label
+    -Wunused-local-typedefs
+    -Wunused-macros
+    -Wunused-parameter
+    -Wunused-result
+    -Wunused-value
+    -Wunused-variable
+    -Wuseless-cast
+    -Wvarargs
+    -Wvariadic-macros
+    -Wvector-operation-performance
+    -Wvexing-parse
+    -Wvirtual-inheritance
+    -Wvirtual-move-assign
+    -Wvla
+    -Wvla-parameter
+    -Wvolatile
+    -Wvolatile-register-var
+    -Wwrite-strings
+    -Wzero-as-null-pointer-constant
+    -Wzero-length-bounds
+)

 add_custom_target(ci_test_gcc
-    COMMAND CXX=${GCC_TOOL} CXXFLAGS=${GCC_CXXFLAGS} ${CMAKE_COMMAND}
+    COMMAND CXX=${GCC_TOOL} CXXFLAGS="${GCC_CXXFLAGS}" ${CMAKE_COMMAND}
        -DCMAKE_BUILD_TYPE=Debug -GNinja
        -DJSON_BuildTests=ON -DJSON_MultipleHeaders=ON
        -S${PROJECT_SOURCE_DIR} -B${PROJECT_BINARY_DIR}/build_gcc
@ -406,7 +419,7 @@ add_custom_target(ci_test_gcc
 )

 add_custom_target(ci_test_clang
-    COMMAND CXX=${CLANG_TOOL} CXXFLAGS=${CLANG_CXXFLAGS} ${CMAKE_COMMAND}
+    COMMAND CXX=${CLANG_TOOL} CXXFLAGS="${CLANG_CXXFLAGS}" ${CMAKE_COMMAND}
        -DCMAKE_BUILD_TYPE=Debug -GNinja
        -DJSON_BuildTests=ON -DJSON_MultipleHeaders=ON
        -S${PROJECT_SOURCE_DIR} -B${PROJECT_BINARY_DIR}/build_clang
@ -421,10 +434,10 @@ add_custom_target(ci_test_clang

 foreach(CXX_STANDARD 11 14 17 20)
    add_custom_target(ci_test_gcc_cxx${CXX_STANDARD}
-        COMMAND CXX=${GCC_TOOL} ${CMAKE_COMMAND}
+        COMMAND CXX=${GCC_TOOL} CXXFLAGS="${GCC_CXXFLAGS}" ${CMAKE_COMMAND}
            -DCMAKE_BUILD_TYPE=Debug -GNinja
-            -DCMAKE_CXX_STANDARD=${CXX_STANDARD} -DCMAKE_CXX_STANDARD_REQUIRED=ON
            -DJSON_BuildTests=ON -DJSON_FastTests=ON
+            -DJSON_TestStandards=${CXX_STANDARD}
            -S${PROJECT_SOURCE_DIR} -B${PROJECT_BINARY_DIR}/build_gcc_cxx${CXX_STANDARD}
        COMMAND ${CMAKE_COMMAND} --build ${PROJECT_BINARY_DIR}/build_gcc_cxx${CXX_STANDARD}
        COMMAND cd ${PROJECT_BINARY_DIR}/build_gcc_cxx${CXX_STANDARD} && ${CMAKE_CTEST_COMMAND} --parallel ${N} --output-on-failure
@ -432,10 +445,10 @@ foreach(CXX_STANDARD 11 14 17 20)
    )

    add_custom_target(ci_test_clang_cxx${CXX_STANDARD}
-        COMMAND CXX=${CLANG_TOOL} ${CMAKE_COMMAND}
+        COMMAND CXX=${CLANG_TOOL} CXXFLAGS="${CLANG_CXXFLAGS}" ${CMAKE_COMMAND}
            -DCMAKE_BUILD_TYPE=Debug -GNinja
-            -DCMAKE_CXX_STANDARD=${CXX_STANDARD} -DCMAKE_CXX_STANDARD_REQUIRED=ON
-            -DJSON_BuildTests=ON
+            -DJSON_BuildTests=ON -DJSON_FastTests=ON
+            -DJSON_TestStandards=${CXX_STANDARD}
            -S${PROJECT_SOURCE_DIR} -B${PROJECT_BINARY_DIR}/build_clang_cxx${CXX_STANDARD}
        COMMAND ${CMAKE_COMMAND} --build ${PROJECT_BINARY_DIR}/build_clang_cxx${CXX_STANDARD}
        COMMAND cd ${PROJECT_BINARY_DIR}/build_clang_cxx${CXX_STANDARD} && ${CMAKE_CTEST_COMMAND} --parallel ${N} --output-on-failure
@ -756,50 +769,67 @@ add_custom_target(ci_benchmarks
 # CMake flags
 ###############################################################################

-if (APPLE)
-    set(CMAKE_310_BINARY ${PROJECT_BINARY_DIR}/cmake-3.1.0-Darwin64/CMake.app/Contents/bin/cmake)
-    add_custom_command(
-        OUTPUT ${CMAKE_310_BINARY}
-        COMMAND wget https://github.com/Kitware/CMake/releases/download/v3.1.0/cmake-3.1.0-Darwin64.tar.gz
-        COMMAND tar xfz cmake-3.1.0-Darwin64.tar.gz
-        COMMAND rm cmake-3.1.0-Darwin64.tar.gz
-        WORKING_DIRECTORY ${PROJECT_BINARY_DIR}
-        COMMENT "Download CMake 3.1.0"
-    )
-else()
-    set(CMAKE_310_BINARY ${PROJECT_BINARY_DIR}/cmake-3.1.0-Linux-x86_64/bin/cmake)
-    add_custom_command(
-        OUTPUT ${CMAKE_310_BINARY}
-        COMMAND wget https://github.com/Kitware/CMake/releases/download/v3.1.0/cmake-3.1.0-Linux-x86_64.tar.gz
-        COMMAND tar xfz cmake-3.1.0-Linux-x86_64.tar.gz
-        COMMAND rm cmake-3.1.0-Linux-x86_64.tar.gz
-        WORKING_DIRECTORY ${PROJECT_BINARY_DIR}
-        COMMENT "Download CMake 3.1.0"
-    )
-endif()
+function(ci_get_cmake version var)
+    if (APPLE)
+        set(${var} ${PROJECT_BINARY_DIR}/cmake-${version}-Darwin64/CMake.app/Contents/bin/cmake)
+        add_custom_command(
+            OUTPUT ${${var}}
+            COMMAND wget -nc https://github.com/Kitware/CMake/releases/download/v${version}/cmake-${version}-Darwin64.tar.gz
+            COMMAND tar xfz cmake-${version}-Darwin64.tar.gz
+            COMMAND rm cmake-${version}-Darwin64.tar.gz
+            WORKING_DIRECTORY ${PROJECT_BINARY_DIR}
+            COMMENT "Download CMake ${version}"
+        )
+    else()
+        set(${var} ${PROJECT_BINARY_DIR}/cmake-${version}-Linux-x86_64/bin/cmake)
+        add_custom_command(
+            OUTPUT ${${var}}
+            COMMAND wget -nc https://github.com/Kitware/CMake/releases/download/v${version}/cmake-${version}-Linux-x86_64.tar.gz
+            COMMAND tar xfz cmake-${version}-Linux-x86_64.tar.gz
+            COMMAND rm cmake-${version}-Linux-x86_64.tar.gz
+            WORKING_DIRECTORY ${PROJECT_BINARY_DIR}
+            COMMENT "Download CMake ${version}"
+        )
+    endif()
+    set(${var} ${${var}} PARENT_SCOPE)
+endfunction()

-set(JSON_CMAKE_FLAGS "JSON_BuildTests;JSON_Install;JSON_MultipleHeaders;JSON_ImplicitConversions;JSON_Valgrind;JSON_Diagnostics;JSON_SystemInclude")
+ci_get_cmake(3.1.0 CMAKE_3_1_0_BINARY)
+ci_get_cmake(3.13.0 CMAKE_3_13_0_BINARY)

-foreach(JSON_CMAKE_FLAG ${JSON_CMAKE_FLAGS})
-    string(TOLOWER "ci_cmake_flag_${JSON_CMAKE_FLAG}" JSON_CMAKE_FLAG_TARGET)
-    add_custom_target("${JSON_CMAKE_FLAG_TARGET}"
-        COMMENT "Check CMake flag ${JSON_CMAKE_FLAG} (CMake ${CMAKE_VERSION})"
+set(JSON_CMAKE_FLAGS_3_1_0 "JSON_Install;JSON_MultipleHeaders;JSON_ImplicitConversions;JSON_Valgrind;JSON_Diagnostics;JSON_SystemInclude")
+set(JSON_CMAKE_FLAGS_3_13_0 "JSON_BuildTests")
+
+function(ci_add_cmake_flags_targets flag min_version)
+    string(TOLOWER "ci_cmake_flag_${flag}" flag_target)
+    string(REPLACE . _ min_version_var ${min_version})
+    set(cmake_binary ${CMAKE_${min_version_var}_BINARY})
+    add_custom_target(${flag_target}
+        COMMENT "Check CMake flag ${flag} (CMake ${CMAKE_VERSION})"
        COMMAND ${CMAKE_COMMAND}
            -Werror=dev
-            -D${JSON_CMAKE_FLAG}=ON
-            -S${PROJECT_SOURCE_DIR} -B${PROJECT_BINARY_DIR}/build_${JSON_CMAKE_FLAG_TARGET}
+            -D${flag}=ON
+            -S${PROJECT_SOURCE_DIR} -B${PROJECT_BINARY_DIR}/build_${flag_target}
    )
-    add_custom_target("${JSON_CMAKE_FLAG_TARGET}_31"
-        COMMENT "Check CMake flag ${JSON_CMAKE_FLAG} (CMake 3.1)"
-        COMMAND mkdir ${PROJECT_BINARY_DIR}/build_${JSON_CMAKE_FLAG_TARGET}_31
-        COMMAND cd ${PROJECT_BINARY_DIR}/build_${JSON_CMAKE_FLAG_TARGET}_31 && ${CMAKE_310_BINARY}
-            -Werror=dev ${PROJECT_SOURCE_DIR}
-            -D${JSON_CMAKE_FLAG}=ON
-            -DCMAKE_CXX_COMPILE_FEATURES="cxx_range_for" -DCMAKE_CXX_FLAGS="-std=gnu++11"
-        DEPENDS ${CMAKE_310_BINARY}
+    add_custom_target(${flag_target}_${min_version_var}
+        COMMENT "Check CMake flag ${JSON_CMAKE_FLAG} (CMake ${min_version})"
+        COMMAND mkdir -pv ${PROJECT_BINARY_DIR}/build_${flag_target}_${min_version_var}
+        COMMAND cd ${PROJECT_BINARY_DIR}/build_${flag_target}_${min_version_var}
+            && ${cmake_binary} -Werror=dev ${PROJECT_SOURCE_DIR} -D${flag}=ON
+        DEPENDS ${cmake_binary}
    )
-    list(APPEND JSON_CMAKE_FLAG_TARGETS ${JSON_CMAKE_FLAG_TARGET} ${JSON_CMAKE_FLAG_TARGET}_31)
-    list(APPEND JSON_CMAKE_FLAG_BUILD_DIRS ${PROJECT_BINARY_DIR}/build_${JSON_CMAKE_FLAG_TARGET} ${PROJECT_BINARY_DIR}/build_${JSON_CMAKE_FLAG_TARGET}_31)
+    list(APPEND JSON_CMAKE_FLAG_TARGETS ${JSON_CMAKE_FLAG_TARGET} ${flag_target}_${min_version_var})
+    list(APPEND JSON_CMAKE_FLAG_BUILD_DIRS ${PROJECT_BINARY_DIR}/build_${flag_target} ${PROJECT_BINARY_DIR}/build_${flag_target}_${min_version_var})
+    set(JSON_CMAKE_FLAG_TARGETS ${JSON_CMAKE_FLAG_TARGETS} PARENT_SCOPE)
+    set(JSON_CMAKE_FLAG_BUILD_DIRS ${JSON_CMAKE_FLAG_BUILD_DIRS} PARENT_SCOPE)
+endfunction()
+
+foreach(JSON_CMAKE_FLAG ${JSON_CMAKE_FLAGS_3_1_0})
+    ci_add_cmake_flags_targets(${JSON_CMAKE_FLAG} 3.1.0)
+endforeach()
+
+foreach(JSON_CMAKE_FLAG ${JSON_CMAKE_FLAGS_3_13_0})
+    ci_add_cmake_flags_targets(${JSON_CMAKE_FLAG} 3.13.0)
 endforeach()

 add_custom_target(ci_cmake_flags
--- a/cmake/test.cmake
+++ b/cmake/test.cmake
@ -0,0 +1,204 @@
+set(_json_test_cmake_list_file ${CMAKE_CURRENT_LIST_FILE})
+
+#############################################################################
+# download test data
+#############################################################################
+
+include(download_test_data)
+
+# test fixture to download test data
+add_test(NAME "download_test_data" COMMAND ${CMAKE_COMMAND} --build ${CMAKE_BINARY_DIR}
+    --target download_test_data
+)
+set_tests_properties(download_test_data PROPERTIES FIXTURES_SETUP TEST_DATA)
+
+if(JSON_Valgrind)
+    find_program(CMAKE_MEMORYCHECK_COMMAND valgrind)
+    message(STATUS "Executing test suite with Valgrind (${CMAKE_MEMORYCHECK_COMMAND})")
+    set(memcheck_command "${CMAKE_MEMORYCHECK_COMMAND} ${CMAKE_MEMORYCHECK_COMMAND_OPTIONS} --error-exitcode=1 --leak-check=full")
+    separate_arguments(memcheck_command)
+endif()
+
+#############################################################################
+# detect standard support
+#############################################################################
+
+# C++11 is the minimum required
+set(compiler_supports_cpp_11 TRUE)
+
+foreach(feature ${CMAKE_CXX_COMPILE_FEATURES})
+    if (${feature} STREQUAL cxx_std_14)
+        set(compiler_supports_cpp_14 TRUE)
+    elseif (${feature} STREQUAL cxx_std_17)
+        set(compiler_supports_cpp_17 TRUE)
+    elseif (${feature} STREQUAL cxx_std_20)
+        set(compiler_supports_cpp_20 TRUE)
+    elseif (${feature} STREQUAL cxx_std_23)
+        set(compiler_supports_cpp_23 TRUE)
+    endif()
+endforeach()
+
+#############################################################################
+# test functions
+#############################################################################
+
+#############################################################################
+# json_test_set_test_options(
+#     all|<tests>
+#     [CXX_STANDARDS all|<args>...]
+#     [COMPILE_DEFINITIONS <args>...]
+#     [COMPILE_FEATURES <args>...]
+#     [COMPILE_OPTIONS <args>...]
+#     [LINK_LIBRARIES <args>...]
+#     [LINK_OPTIONS <args>...])
+#
+# Supply test- and standard-specific build settings.
+# Specify multiple tests using a list e.g., "test-foo;test-bar".
+#
+# Must be called BEFORE the test is created.
+#############################################################################
+
+function(json_test_set_test_options tests)
+    cmake_parse_arguments(args "" ""
+        "CXX_STANDARDS;COMPILE_DEFINITIONS;COMPILE_FEATURES;COMPILE_OPTIONS;LINK_LIBRARIES;LINK_OPTIONS"
+        ${ARGN})
+
+    if(NOT args_CXX_STANDARDS)
+        set(args_CXX_STANDARDS "all")
+    endif()
+
+    foreach(test ${tests})
+        if("${test}" STREQUAL "all")
+            set(test "")
+        endif()
+
+        foreach(cxx_standard ${args_CXX_STANDARDS})
+            if("${cxx_standard}" STREQUAL "all")
+                if("${test}" STREQUAL "")
+                    message(FATAL_ERROR "Not supported. Change defaults in: ${_json_test_cmake_list_file}")
+                endif()
+                set(test_interface _json_test_interface_${test})
+            else()
+                set(test_interface _json_test_interface_${test}_cpp_${cxx_standard})
+            endif()
+
+            if(NOT TARGET ${test_interface})
+                add_library(${test_interface} INTERFACE)
+            endif()
+
+            target_compile_definitions(${test_interface} INTERFACE ${args_COMPILE_DEFINITIONS})
+            target_compile_features(${test_interface} INTERFACE ${args_COMPILE_FEATURES})
+            target_compile_options(${test_interface} INTERFACE ${args_COMPILE_OPTIONS})
+            target_link_libraries (${test_interface} INTERFACE ${args_LINK_LIBRARIES})
+            target_link_options(${test_interface} INTERFACE ${args_LINK_OPTIONS})
+        endforeach()
+    endforeach()
+endfunction()
+
+# for internal use by json_test_add_test_for()
+function(_json_test_add_test test_name file main cxx_standard)
+    set(test_target ${test_name}_cpp${cxx_standard})
+
+    if(TARGET ${test_target})
+        message(FATAL_ERROR "Target ${test_target} has already been added.")
+    endif()
+
+    add_executable(${test_target} ${file})
+    target_link_libraries(${test_target} PRIVATE ${main})
+
+    # set and require C++ standard
+    set_target_properties(${test_target} PROPERTIES
+        CXX_STANDARD ${cxx_standard}
+        CXX_STANDARD_REQUIRED ON
+    )
+
+    # apply standard-specific build settings
+    if(TARGET _json_test_interface__cpp_${cxx_standard})
+        target_link_libraries(${test_target} PRIVATE _json_test_interface__cpp_${cxx_standard})
+    endif()
+
+    # apply test-specific build settings
+    if(TARGET _json_test_interface_${test_name})
+        target_link_libraries(${test_target} PRIVATE _json_test_interface_${test_name})
+    endif()
+
+    # apply test- and standard-specific build settings
+    if(TARGET _json_test_interface_${test_name}_cpp_${cxx_standard})
+        target_link_libraries(${test_target} PRIVATE
+            _json_test_interface_${test_name}_cpp_${cxx_standard}
+        )
+    endif()
+
+    if (JSON_FastTests)
+        add_test(NAME ${test_target}
+            COMMAND ${test_target} ${DOCTEST_TEST_FILTER}
+            WORKING_DIRECTORY ${CMAKE_SOURCE_DIR}
+        )
+    else()
+        add_test(NAME ${test_target}
+            COMMAND ${test_target} ${DOCTEST_TEST_FILTER} --no-skip
+            WORKING_DIRECTORY ${CMAKE_SOURCE_DIR}
+        )
+    endif()
+    set_tests_properties(${test_target} PROPERTIES LABELS "all" FIXTURES_REQUIRED TEST_DATA)
+
+    if(JSON_Valgrind)
+        add_test(NAME ${test_target}_valgrind
+            COMMAND ${memcheck_command} $<TARGET_FILE:${test_target}> ${DOCTEST_TEST_FILTER}
+            WORKING_DIRECTORY ${CMAKE_SOURCE_DIR}
+        )
+        set_tests_properties(${test_target}_valgrind PROPERTIES
+            LABELS "valgrind" FIXTURES_REQUIRED TEST_DATA
+        )
+    endif()
+endfunction()
+
+#############################################################################
+# json_test_add_test_for(
+#     <file>
+#     MAIN <main>
+#     [CXX_STANDARDS <version_number>...] [FORCE])
+#
+# Given a <file> unit-foo.cpp, produces
+#
+#     test-foo_cpp<version_number>
+#
+# if C++ standard <version_number> is supported by the compiler and the
+# source file contains JSON_HAS_CPP_<version_number>.
+# Use FORCE to create the test regardless of the file containing
+# JSON_HAS_CPP_<version_number>.
+# Test targets are linked against <main>.
+# CXX_STANDARDS defaults to "11".
+#############################################################################
+
+function(json_test_add_test_for file)
+    cmake_parse_arguments(args "FORCE" "MAIN" "CXX_STANDARDS" ${ARGN})
+
+    get_filename_component(file_basename ${file} NAME_WE)
+    string(REGEX REPLACE "unit-([^$]+)" "test-\\1" test_name ${file_basename})
+
+    if("${args_MAIN}" STREQUAL "")
+        message(FATAL_ERROR "Required argument MAIN <main> missing.")
+    endif()
+
+    if("${args_CXX_STANDARDS}" STREQUAL "")
+        set(args_CXX_STANDARDS 11)
+    endif()
+
+    file(READ ${file} file_content)
+    foreach(cxx_standard ${args_CXX_STANDARDS})
+        if(NOT compiler_supports_cpp_${cxx_standard})
+            continue()
+        endif()
+
+        # add unconditionally if C++11 (default) or forced
+        if(NOT ("${cxx_standard}" STREQUAL 11 OR args_FORCE))
+            string(FIND "${file_content}" JSON_HAS_CPP_${cxx_standard} has_cpp_found)
+            if(${has_cpp_found} EQUAL -1)
+                continue()
+            endif()
+        endif()
+
+        _json_test_add_test(${test_name} ${file} ${args_MAIN} ${cxx_standard})
+    endforeach()
+endfunction()
--- a/doc/mkdocs/docs/api/basic_json/operator_literal_json_pointer.md
+++ b/doc/mkdocs/docs/api/basic_json/operator_literal_json_pointer.md
@ -43,6 +43,10 @@ Linear.
    --8<-- "examples/operator_literal_json_pointer.output"
    ```

+## See also
+
+- [json_pointer](../json_pointer/index.md) - type to represent JSON Pointers
+
 ## Version history

 - Added in version 2.0.0.
--- a/doc/mkdocs/docs/api/json_pointer/index.md
+++ b/doc/mkdocs/docs/api/json_pointer/index.md
@ -29,6 +29,7 @@ are the base for JSON patches.

 ## See also

+- [operator""_json_pointer](../basic_json/operator_literal_json_pointer.md) - user-defined string literal for JSON pointers
 - [RFC 6901](https://datatracker.ietf.org/doc/html/rfc6901)

 ## Version history
--- a/doc/mkdocs/docs/features/arbitrary_types.md
+++ b/doc/mkdocs/docs/features/arbitrary_types.md
@ -85,29 +85,31 @@ Some important things:

 If you just want to serialize/deserialize some structs, the `to_json`/`from_json` functions can be a lot of boilerplate.

-There are two macros to make your life easier as long as you (1) want to use a JSON object as serialization and (2) want to use the member variable names as object keys in that object:
+There are four macros to make your life easier as long as you (1) want to use a JSON object as serialization and (2) want to use the member variable names as object keys in that object:

- `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(name, member1, member2, ...)` is to be defined inside the namespace of the class/struct to create code for.
- `NLOHMANN_DEFINE_TYPE_INTRUSIVE(name, member1, member2, ...)` is to be defined inside the class/struct to create code for. This macro can also access private members.
+- `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(name, member1, member2, ...)` is to be defined inside the namespace of the class/struct to create code for. It will throw an exception in `from_json()` due to a missing value in the JSON object.
+- `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT(name, member1, member2, ...)` is to be defined inside the namespace of the class/struct to create code for. It will not throw an exception in `from_json()` due to a missing value in the JSON object, but fills in values from object which is default-constructed by the type.
+- `NLOHMANN_DEFINE_TYPE_INTRUSIVE(name, member1, member2, ...)` is to be defined inside the class/struct to create code for. This macro can also access private members. It will throw an exception in `from_json()` due to a missing value in the JSON object.
+- `NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT(name, member1, member2, ...)` is to be defined inside the class/struct to create code for. This macro can also access private members. It will not throw an exception in `from_json()` due to a missing value in the JSON object, but fills in values from object which is default-constructed by the type.

-In both macros, the first parameter is the name of the class/struct, and all remaining parameters name the members.
+In all macros, the first parameter is the name of the class/struct, and all remaining parameters name the members. You can read more docs about them starting from [here](macros.md#nlohmann_define_type_intrusivetype-member).

 !!! note

-    At most 64 member variables can be passed to `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE` or `NLOHMANN_DEFINE_TYPE_INTRUSIVE`.
+    At most 64 member variables can be passed to these macros.

 ??? example

    The `to_json`/`from_json` functions for the `person` struct above can be created with:
-    
+
    ```cpp
    namespace ns {
        NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(person, name, address, age)
    }
    ```
-    
+
    Here is an example with private members, where `NLOHMANN_DEFINE_TYPE_INTRUSIVE` is needed:
-    
+
    ```cpp
    namespace ns {
        class address {
@ -115,7 +117,7 @@ In both macros, the first parameter is the name of the class/struct, and all rem
            std::string street;
            int housenumber;
            int postcode;
-            
+
          public:
            NLOHMANN_DEFINE_TYPE_INTRUSIVE(address, street, housenumber, postcode)
        };
--- a/doc/mkdocs/docs/features/json_pointer.md
+++ b/doc/mkdocs/docs/features/json_pointer.md
@ -1,19 +1,123 @@
 # JSON Pointer

-The library supports **JSON Pointer** ([RFC 6901](https://tools.ietf.org/html/rfc6901)) as alternative means to address structured values.
+## Introduction
+
+The library supports **JSON Pointer** ([RFC 6901](https://tools.ietf.org/html/rfc6901)) as alternative means to address
+structured values. A JSON Pointer is a string that identifies a specific value withing a JSON document.
+
+Consider the following JSON document
+
+```json
+{
+    "array": ["A", "B", "C"],
+    "nested": {
+        "one": 1,
+        "two": 2,
+        "three": [true, false]
+    }
+}
+```
+
+Then every value inside the JSON document can be idientified as follows:
+
+| JSON Pointer      | JSON value                                                                       |
+|-------------------|----------------------------------------------------------------------------------|
+| `/`               | `#!json {"array":["A","B","C"],"nested":{"one":1,"two":2,"three":[true,false]}}` |
+| `/array`          | `#!json ["A","B","C"]`                                                           |
+| `/array/0`        | `#!json A`                                                                       |
+| `/array/1`        | `#!json B`                                                                       |
+| `/array/2`        | `#!json C`                                                                       |
+| `/nested`         | `#!json {"one":1,"two":2,"three":[true,false]}`                                  |
+| `/nested/one`     | `#!json 1`                                                                       |
+| `/nested/two`     | `#!json 2`                                                                       |
+| `/nested/three`   | `#!json [true,false]`                                                            |
+| `/nested/three/0` | `#!json true`                                                                    |
+| `/nested/three/1` | `#!json false`                                                                   |
+
+## JSON Pointer creation
+
+JSON Pointers can be created from a string:

 ```cpp
-// a JSON value
-json j_original = R"({
-  "baz": ["one", "two", "three"],
-  "foo": "bar"
-})"_json;
+json::json_pointer p = "/nested/one";
+```

-// access members with a JSON pointer (RFC 6901)
-j_original["/baz/1"_json_pointer];
-// "two"
+Furthermore, a user-defined string literal can be used to achieve the same result:
+
+```cpp
+auto p = "/nested/one"_json_pointer;
+```
+
+The escaping rules of [RFC 6901](https://tools.ietf.org/html/rfc6901) are implemented. See the
+[constructor documentation](../api/json_pointer/json_pointer.md) for more information.
+
+## Value access
+
+JSON Pointers can be used in the [`at`](../api/basic_json/at.md), [`operator[]`](../api/basic_json/operator%5B%5D.md),
+and [`value`](../api/basic_json/value.md) functions just like object keys or array indices.
+
+```cpp
+// the JSON value from above
+auto j = json::parse(R"({
+    "array": ["A", "B", "C"],
+    "nested": {
+        "one": 1,
+        "two": 2,
+        "three": [true, false]
+    }
+})");
+
+// access values
+auto val = j["/"_json_pointer];                             // {"array":["A","B","C"],...}
+auto val1 = j["/nested/one"_json_pointer];                  // 1
+auto val2 = j.at[json::json_pointer("/nested/three/1")];    // false
+auto val3 = j.value[json::json_pointer("/nested/four", 0)]; // 0
+```
+
+## Flatten / unflatten
+
+The library implements a function [`flatten`](../api/basic_json/flatten.md) to convert any JSON document into a JSON
+object where each key is a JSON Pointer and each value is a primitive JSON value (i.e., a string, boolean, number, or
+null).
+
+```cpp
+// the JSON value from above
+auto j = json::parse(R"({
+    "array": ["A", "B", "C"],
+    "nested": {
+        "one": 1,
+        "two": 2,
+        "three": [true, false]
+    }
+})");
+
+// create flattened value
+auto j_flat = j.flatten();
+```
+
+The resulting value `j_flat` is:
+
+```json
+{
+  "/array/0": "A",
+  "/array/1": "B",
+  "/array/2": "C",
+  "/nested/one": 1,
+  "/nested/two": 2,
+  "/nested/three/0": true,
+  "/nested/three/1": false
+}
+```
+
+The reverse function, [`unflatten`](../api/basic_json/unflatten.md) recreates the original value.
+
+```cpp
+auto j_original = j_flat.unflatten();
 ```

 ## See also

 - Class [`json_pointer`](../api/json_pointer/index.md)
+- Function [`flatten`](../api/basic_json/flatten.md)
+- Function [`unflatten`](../api/basic_json/unflatten.md)
+- [JSON Patch](json_patch.md)
--- a/doc/mkdocs/docs/features/macros.md
+++ b/doc/mkdocs/docs/features/macros.md
@ -4,16 +4,41 @@ Some aspects of the library can be configured by defining preprocessor macros be

 ## `JSON_ASSERT(x)`

-The default value is `#!cpp assert(x)`.
+This macro controls which code is executed for runtime assertions of the libraries.
+
+!!! info "Default behavior"
+
+    The default value is [`#!cpp assert(x)`](https://en.cppreference.com/w/cpp/error/assert).
+
+    ```cpp
+    #define JSON_ASSERT(x) assert(x)
+    ```

 ## `JSON_CATCH_USER(exception)`

-This macro overrides `#!cpp catch` calls inside the library. The argument is the type of the exception to catch. As of
-version 3.8.0, the library only catches `std::out_of_range` exceptions internally to rethrow them as
-[`json::out_of_range`](../home/exceptions.md#out-of-range) exceptions. The macro is always followed by a scope.
+This macro overrides [`#!cpp catch`](https://en.cppreference.com/w/cpp/language/try_catch) calls inside the library.
+The argument is the type of the exception to catch. As of version 3.8.0, the library only catches `std::out_of_range`
+exceptions internally to rethrow them as [`json::out_of_range`](../home/exceptions.md#out-of-range) exceptions. The
+macro is always followed by a scope.

 See [Switch off exceptions](../home/exceptions.md#switch-off-exceptions) for an example.

+!!! info "Default behavior"
+
+    When exceptions are enabled, the default value is
+    [`#!cpp catch(exception)`](https://en.cppreference.com/w/cpp/language/try_catch).
+
+    ```cpp
+    #define JSON_CATCH_USER(exception) catch(exception)
+    ```
+
+    When exceptions are switched off by the compiler, the default value is `#!cpp if (false)` to make the catch block
+    unreachable.
+
+    ```cpp
+    #define JSON_CATCH_USER(exception) if (false)
+    ```
+
 ## `JSON_DIAGNOSTICS`

 This macro enables extended diagnostics for exception messages. Possible values are `1` to enable or `0` to disable
@ -26,6 +51,18 @@ that enabling this macro increases the size of every JSON value by one pointer a
 The diagnostics messages can also be controlled with the CMake option `JSON_Diagnostics` (`OFF` by default) which sets
 `JSON_DIAGNOSTICS` accordingly.

+!!! warning
+
+    As this macro changes the definition of the `basic_json` object, it MUST be defined in the same way globally, even
+    across different compilation units; DO NOT link together code compiled with different definitions of
+    `JSON_DIAGNOSTICS` as this is a violation of the One Definition Rule and will cause undefined behaviour.
+
+!!! info "Default behavior"
+
+    ```cpp
+    #define JSON_DIAGNOSTICS 0
+    ```
+
 ## `JSON_HAS_CPP_11`, `JSON_HAS_CPP_14`, `JSON_HAS_CPP_17`, `JSON_HAS_CPP_20`

 The library targets C++11, but also supports some features introduced in later C++ versions (e.g., `std::string_view`
@ -34,6 +71,11 @@ standard. By defining any of these symbols, the internal check is overridden and
 unconditionally assumed. This can be helpful for compilers that only implement parts of the standard and would be
 detected incorrectly.

+!!! info "Default behavior"
+
+    The default value is detected based on the preprocessor macros `#!cpp __cplusplus`, `#!cpp _HAS_CXX17`, or
+    `#!cpp _MSVC_LANG`.
+
 ## `JSON_HAS_FILESYSTEM`, `JSON_HAS_EXPERIMENTAL_FILESYSTEM`

 When compiling with C++17, the library provides conversions from and to `std::filesystem::path`. As compiler support
@ -41,12 +83,29 @@ for filesystem is limited, the library tries to detect whether `<filesystem>`/`s
 or `<experimental/filesystem>`/`std::experimental::filesystem` (`JSON_HAS_EXPERIMENTAL_FILESYSTEM`) should be used.
 To override the built-in check, define `JSON_HAS_FILESYSTEM` or `JSON_HAS_EXPERIMENTAL_FILESYSTEM` to `1`.

+!!! info "Default behavior"
+
+    The default value is detected based on the preprocessor macros `#!cpp __cpp_lib_filesystem`,
+    `#!cpp __cpp_lib_experimental_filesystem`, `#!cpp __has_include(<filesystem>)`, or
+    `#!cpp __has_include(<experimental/filesystem>)`.
+
+Note that older compilers or older versions of libstd++ also require the library `stdc++fs` to be linked to for
+filesystem support.
+
 ## `JSON_NOEXCEPTION`

 Exceptions can be switched off by defining the symbol `JSON_NOEXCEPTION`. When defining `JSON_NOEXCEPTION`, `#!cpp try`
 is replaced by `#!cpp if (true)`, `#!cpp catch` is replaced by `#!cpp if (false)`, and `#!cpp throw` is replaced by
 `#!cpp std::abort()`.

+!!! info "Default behavior"
+
+    By default, the macro is not defined.
+
+    ```cpp
+    #undef JSON_NOEXCEPTION
+    ```
+
 The same effect is achieved by setting the compiler flag `-fno-exceptions`.

 Note the explanatory [`what()`](https://en.cppreference.com/w/cpp/error/exception/what) string of exceptions is not
@ -58,23 +117,72 @@ When defined, headers `<cstdio>`, `<ios>`, `<iosfwd>`, `<istream>`, and `<ostrea
 relying on these headers are excluded. This is relevant for environment where these I/O functions are disallowed for
 security reasons (e.g., Intel Software Guard Extensions (SGX)).

+!!! info "Default behavior"
+
+    By default, the macro is not defined.
+
+    ```cpp
+    #undef JSON_NO_IO
+    ```
+
 ## `JSON_SKIP_UNSUPPORTED_COMPILER_CHECK`

 When defined, the library will not create a compile error when a known unsupported compiler is detected. This allows to
 use the library with compilers that do not fully support C++11 and may only work if unsupported features are not used.

+!!! info "Default behavior"
+
+    By default, the macro is not defined.
+
+    ```cpp
+    #undef JSON_SKIP_UNSUPPORTED_COMPILER_CHECK
+    ```
+
 ## `JSON_THROW_USER(exception)`

 This macro overrides `#!cpp throw` calls inside the library. The argument is the exception to be thrown. Note that
 `JSON_THROW_USER` should leave the current scope (e.g., by throwing or aborting), as continuing after it may yield
 undefined behavior.

+!!! info "Default behavior"
+
+    When exceptions are enabled, the default value is
+    [`#!cpp throw exception`](https://en.cppreference.com/w/cpp/language/throw).
+
+    ```cpp
+    #define JSON_THROW_USER(exception) throw exception
+    ```
+
+    When exceptions are switched off by the compiler, the default value is
+    [`#!cpp std::abort()`](https://en.cppreference.com/w/cpp/utility/program/abort) to make reaching the throw branch
+    abort the process.
+
+    ```cpp
+    #define JSON_THROW_USER(exception) std::abort()
+    ```
+
 See [Switch off exceptions](../home/exceptions.md#switch-off-exceptions) for an example.

 ## `JSON_TRY_USER`

 This macro overrides `#!cpp try` calls inside the library. It has no arguments and is always followed by a scope.

+!!! info "Default behavior"
+
+    When exceptions are enabled, the default value is
+    [`#!cpp try`](https://en.cppreference.com/w/cpp/language/try_catch).
+
+    ```cpp
+    #define JSON_TRY_USER try
+    ```
+
+    When exceptions are switched off by the compiler, the default value is `#!cpp if (true)` to unconditionally execute
+    the following code block.
+
+    ```cpp
+    #define JSON_TRY_USER if (true)
+    ```
+
 See [Switch off exceptions](../home/exceptions.md#switch-off-exceptions) for an example.

 ## `JSON_USE_IMPLICIT_CONVERSIONS`
@ -84,12 +192,12 @@ When defined to `0`, implicit conversions are switched off. By default, implicit
 ??? example

    This is an example for an implicit conversion:
-    
+
    ```cpp
    json j = "Hello, world!";
    std::string s = j;
    ```
-    
+
    When `JSON_USE_IMPLICIT_CONVERSIONS` is defined to `0`, the code above does no longer compile. Instead, it must be
    written like this:

@ -101,6 +209,12 @@ When defined to `0`, implicit conversions are switched off. By default, implicit
 Implicit conversions can also be controlled with the CMake option `JSON_ImplicitConversions` (`ON` by default) which
 sets `JSON_USE_IMPLICIT_CONVERSIONS` accordingly.

+!!! info "Default behavior"
+
+    ```cpp
+    #define JSON_USE_IMPLICIT_CONVERSIONS 1
+    ```
+
 ## `NLOHMANN_DEFINE_TYPE_INTRUSIVE(type, member...)`

 This macro can be used to simplify the serialization/deserialization of types if (1) want to use a JSON object as
@ -112,6 +226,10 @@ The first parameter is the name of the class/struct, and all remaining parameter

 See [Simplify your life with macros](arbitrary_types.md#simplify-your-life-with-macros) for an example.

+## `NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT(type, member...)`
+
+This macro is similar to `NLOHMANN_DEFINE_TYPE_INTRUSIVE`. It will not throw an exception in `from_json()` due to a missing value in the JSON object, but can throw due to a mismatched type. In order to support that it requires that the type be default constructible. The `from_json()` function default constructs an object and uses its values as the defaults when calling the `value()` function.
+
 ## `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(type, member...)`

 This macro can be used to simplify the serialization/deserialization of types if (1) want to use a JSON object as
@ -123,6 +241,10 @@ first parameter is the name of the class/struct, and all remaining parameters na

 See [Simplify your life with macros](arbitrary_types.md#simplify-your-life-with-macros) for an example.

+## `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT(type, member...)`
+
+This macro is similar to `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE`. It will not throw an exception in `from_json()` due to a missing value in the JSON object, but can throw due to a mismatched type. In order to support that it requires that the type be default constructible. The `from_json()` function default constructs an object and uses its values as the defaults when calling the `value()` function.
+
 ## `NLOHMANN_JSON_SERIALIZE_ENUM(type, ...)`

 This macro simplifies the serialization/deserialization of enum types. See
--- a/doc/mkdocs/docs/features/object_order.md
+++ b/doc/mkdocs/docs/features/object_order.md
@ -2,6 +2,8 @@

 The [JSON standard](https://tools.ietf.org/html/rfc8259.html) defines objects as "an unordered collection of zero or more name/value pairs". As such, an implementation does not need to preserve any specific order of object keys.

+## Default behavior: sort keys
+
 The default type `nlohmann::json` uses a `std::map` to store JSON objects, and thus stores object keys **sorted alphabetically**.

 ??? example
@ -33,6 +35,8 @@ The default type `nlohmann::json` uses a `std::map` to store JSON objects, and t
    }
    ```

+## Alternative behavior: preserve insertion order
+
 If you do want to preserve the **insertion order**, you can try the type [`nlohmann::ordered_json`](https://github.com/nlohmann/json/issues/2179).

 ??? example
@ -65,3 +69,58 @@ If you do want to preserve the **insertion order**, you can try the type [`nlohm
    ```

 Alternatively, you can use a more sophisticated ordered map like [`tsl::ordered_map`](https://github.com/Tessil/ordered-map) ([integration](https://github.com/nlohmann/json/issues/546#issuecomment-304447518)) or [`nlohmann::fifo_map`](https://github.com/nlohmann/fifo_map) ([integration](https://github.com/nlohmann/json/issues/485#issuecomment-333652309)).
+
+### Notes on parsing
+
+Note that you also need to call the right [`parse`](../api/basic_json/parse.md) function when reading from a file.
+Assume file `input.json` contains the JSON object above:
+
+```json
+{
+  "one": 1,
+  "two": 2,
+  "three": 3
+}
+```
+
+!!! success "Right way"
+
+    The following code correctly calls the `parse` function from `nlohmann::ordered_json`:
+
+    ```cpp
+    std::ifstream i("input.json");
+    auto j = nlohmann::ordered_json::parse(i);
+    std::cout << j.dump(2) << std::endl;
+    ```
+
+    The output will be:
+
+    ```json
+    {
+      "one": 1,
+      "two": 2,
+      "three": 3
+    }
+    ```
+
+??? failure "Wrong way"
+
+    The following code incorrectly calls the `parse` function from `nlohmann::json` which does not preserve the
+    insertion order, but sorts object keys. Assigning the result to `nlohmann::ordered_json` compiles, but does not
+    restore the order from the input file.
+
+    ```cpp
+    std::ifstream i("input.json");
+    nlohmann::ordered_json j = nlohmann::json::parse(i);
+    std::cout << j.dump(2) << std::endl;
+    ```
+
+    The output will be:
+
+    ```json
+    {
+      "one": 1,
+      "three": 3
+      "two": 2,
+    }
+    ```
--- a/doc/mkdocs/docs/integration/cmake.md
+++ b/doc/mkdocs/docs/integration/cmake.md
@ -2,102 +2,126 @@

 ## Integration

-You can also use the `nlohmann_json::nlohmann_json` interface target in CMake.  This target populates the appropriate usage requirements for `INTERFACE_INCLUDE_DIRECTORIES` to point to the appropriate include directories and `INTERFACE_COMPILE_FEATURES` for the necessary C++11 flags.
+You can use the `nlohmann_json::nlohmann_json` interface target in CMake. This target populates the appropriate usage
+requirements for [`INTERFACE_INCLUDE_DIRECTORIES`](https://cmake.org/cmake/help/latest/prop_tgt/INTERFACE_INCLUDE_DIRECTORIES.html)
+to point to the appropriate include directories and [`INTERFACE_COMPILE_FEATURES`](https://cmake.org/cmake/help/latest/prop_tgt/INTERFACE_COMPILE_FEATURES.html)
+for the necessary C++11 flags.

 ### External

-To use this library from a CMake project, you can locate it directly with `find_package()` and use the namespaced imported target from the generated package configuration:
+To use this library from a CMake project, you can locate it directly with [`find_package()`](https://cmake.org/cmake/help/latest/command/find_package.html)
+and use the namespaced imported target from the generated package configuration:

-```cmake
-# CMakeLists.txt
-find_package(nlohmann_json 3.2.0 REQUIRED)
-...
-add_library(foo ...)
-...
-target_link_libraries(foo PRIVATE nlohmann_json::nlohmann_json)
-```
+!!! example

-The package configuration file, `nlohmann_jsonConfig.cmake`, can be used either from an install tree or directly out of the build tree.
+    ```cmake title="CMakeLists.txt"
+    cmake_minimum_required(VERSION 3.1)
+    project(ExampleProject LANGUAGES CXX)
+    
+    find_package(nlohmann_json 3.10.5 REQUIRED)
+    
+    add_executable(example example.cpp)
+    target_link_libraries(example PRIVATE nlohmann_json::nlohmann_json)
+    ```
+
+The package configuration file, `nlohmann_jsonConfig.cmake`, can be used either from an install tree or directly out of
+the build tree.

 ### Embedded

-To embed the library directly into an existing CMake project, place the entire source tree in a subdirectory and call `add_subdirectory()` in your `CMakeLists.txt` file:
+To embed the library directly into an existing CMake project, place the entire source tree in a subdirectory and call
+`add_subdirectory()` in your `CMakeLists.txt` file.

-```cmake
-# If you only include this third party in PRIVATE source files, you do not
-# need to install it when your main project gets installed.
-# set(JSON_Install OFF CACHE INTERNAL "")
+!!! example

-# Don't use include(nlohmann_json/CMakeLists.txt) since that carries with it
-# unintended consequences that will break the build.  It's generally
-# discouraged (although not necessarily well documented as such) to use
-# include(...) for pulling in other CMake projects anyways.
-add_subdirectory(nlohmann_json)
-...
-add_library(foo ...)
-...
-target_link_libraries(foo PRIVATE nlohmann_json::nlohmann_json)
-```
+    ```cmake title="CMakeLists.txt"
+    cmake_minimum_required(VERSION 3.1)
+    project(ExampleProject LANGUAGES CXX)

-### Embedded (FetchContent)
+    # If you only include this third party in PRIVATE source files, you do not need to install it
+    # when your main project gets installed.
+    set(JSON_Install OFF CACHE INTERNAL "")
+    
+    add_subdirectory(nlohmann_json)

-Since CMake v3.11,
-[FetchContent](https://cmake.org/cmake/help/v3.11/module/FetchContent.html) can
-be used to automatically download the repository as a dependency at configure type.
+    add_executable(example example.cpp)
+    target_link_libraries(example PRIVATE nlohmann_json::nlohmann_json)
+    ```

-Example:
-```cmake
-include(FetchContent)
+!!! note

-FetchContent_Declare(json
-  GIT_REPOSITORY https://github.com/nlohmann/json
-  GIT_TAG v3.7.3)
+    Do not use `#!cmake include(nlohmann_json/CMakeLists.txt)`, since that carries with it unintended consequences that
+    will break the build. It is generally discouraged (although not necessarily well documented as such) to use
+    `#!cmake include(...)` for pulling in other CMake projects anyways.

-FetchContent_GetProperties(json)
-if(NOT json_POPULATED)
-  FetchContent_Populate(json)
-  add_subdirectory(${json_SOURCE_DIR} ${json_BINARY_DIR} EXCLUDE_FROM_ALL)
-endif()
-
-target_link_libraries(foo PRIVATE nlohmann_json::nlohmann_json)
-```
-
-!!! Note
-	The repository <https://github.com/nlohmann/json> download size is quite large.
-	You might want to depend on a smaller repository. For instance, you might want to replace the URL above by
-	<https://github.com/ArthurSonzogni/nlohmann_json_cmake_fetchcontent>.

 ### Supporting Both

-To allow your project to support either an externally supplied or an embedded JSON library, you can use a pattern akin to the following:
+To allow your project to support either an externally supplied or an embedded JSON library, you can use a pattern akin
+to the following.

-``` cmake
-# Top level CMakeLists.txt
-project(FOO)
-...
-option(FOO_USE_EXTERNAL_JSON "Use an external JSON library" OFF)
-...
-add_subdirectory(thirdparty)
-...
-add_library(foo ...)
-...
-# Note that the namespaced target will always be available regardless of the
-# import method
-target_link_libraries(foo PRIVATE nlohmann_json::nlohmann_json)
-```
-```cmake
-# thirdparty/CMakeLists.txt
-...
-if(FOO_USE_EXTERNAL_JSON)
-  find_package(nlohmann_json 3.2.0 REQUIRED)
-else()
-  set(JSON_BuildTests OFF CACHE INTERNAL "")
-  add_subdirectory(nlohmann_json)
-endif()
-...
-```
+!!! example

-`thirdparty/nlohmann_json` is then a complete copy of this source tree.
+    ```cmake title="CMakeLists.txt"
+    project(ExampleProject LANGUAGES CXX)
+
+    option(EXAMPLE_USE_EXTERNAL_JSON "Use an external JSON library" OFF)
+
+    add_subdirectory(thirdparty)
+
+    add_executable(example example.cpp)
+
+    # Note that the namespaced target will always be available regardless of the import method
+    target_link_libraries(example PRIVATE nlohmann_json::nlohmann_json)
+    ```
+    
+    ```cmake title="thirdparty/CMakeLists.txt"
+    if(EXAMPLE_USE_EXTERNAL_JSON)
+        find_package(nlohmann_json 3.10.5 REQUIRED)
+    else()
+        set(JSON_BuildTests OFF CACHE INTERNAL "")
+        add_subdirectory(nlohmann_json)
+    endif()
+    ```
+    
+    `thirdparty/nlohmann_json` is then a complete copy of this source tree.
+
+
+### FetchContent
+
+Since CMake v3.11, [FetchContent](https://cmake.org/cmake/help/v3.11/module/FetchContent.html) can be used to
+automatically download a release as a dependency at configure type.
+
+!!! example
+
+    ```cmake title="CMakeLists.txt"
+    cmake_minimum_required(VERSION 3.11)
+    project(ExampleProject LANGUAGES CXX)
+
+    include(FetchContent)
+    
+    FetchContent_Declare(json URL https://github.com/nlohmann/json/releases/download/v3.10.5/json.tar.xz)
+    FetchContent_MakeAvailable(json)
+    
+    add_executable(example example.cpp)
+    target_link_libraries(example PRIVATE nlohmann_json::nlohmann_json)
+    ```
+
+!!! Note
+
+    It is recommended to use the URL approach described above which is supported as of version 3.10.0. It is also
+    possible to pass the Git repository like
+
+    ```cmake
+    FetchContent_Declare(json
+        GIT_REPOSITORY https://github.com/nlohmann/json
+        GIT_TAG v3.10.5
+    )
+    ```
+
+	However, the repository <https://github.com/nlohmann/json> download size is quite large. You might want to depend on
+    a smaller repository. For instance, you might want to replace the URL in the example by
+    <https://github.com/ArthurSonzogni/nlohmann_json_cmake_fetchcontent>.

 ## CMake Options

--- a/doc/mkdocs/docs/integration/example.cpp
+++ b/doc/mkdocs/docs/integration/example.cpp
@ -1,9 +1,10 @@
 #include <nlohmann/json.hpp>
 #include <iostream>
+#include <iomanip>

 using json = nlohmann::json;

 int main()
 {
-    std::cout << json::meta() << std::endl;
+    std::cout << std::setw(4) << json::meta() << std::endl;
 }
--- a/doc/mkdocs/docs/integration/index.md
+++ b/doc/mkdocs/docs/integration/index.md
@ -1,6 +1,7 @@
 # Header only

-[`json.hpp`](https://github.com/nlohmann/json/blob/develop/single_include/nlohmann/json.hpp) is the single required file in `single_include/nlohmann` or [released here](https://github.com/nlohmann/json/releases). You need to add
+[`json.hpp`](https://github.com/nlohmann/json/blob/develop/single_include/nlohmann/json.hpp) is the single required
+file in `single_include/nlohmann` or [released here](https://github.com/nlohmann/json/releases). You need to add

 ```cpp
 #include <nlohmann/json.hpp>
@ -9,6 +10,9 @@
 using json = nlohmann::json;
 ```

-to the files you want to process JSON and set the necessary switches to enable C++11 (e.g., `-std=c++11` for GCC and Clang).
+to the files you want to process JSON and set the necessary switches to enable C++11 (e.g., `-std=c++11` for GCC and
+Clang).

-You can further use file [`include/nlohmann/json_fwd.hpp`](https://github.com/nlohmann/json/blob/develop/include/nlohmann/json_fwd.hpp) for forward-declarations. The installation of `json_fwd.hpp` (as part of CMake's install step), can be achieved by setting `-DJSON_MultipleHeaders=ON`.
+You can further use file [`include/nlohmann/json_fwd.hpp`](https://github.com/nlohmann/json/blob/develop/include/nlohmann/json_fwd.hpp)
+for forward-declarations. The installation of `json_fwd.hpp` (as part of CMake's install step), can be achieved by
+setting `-DJSON_MultipleHeaders=ON`.
--- a/doc/mkdocs/docs/integration/package_managers.md
+++ b/doc/mkdocs/docs/integration/package_managers.md
@ -6,6 +6,12 @@ Throughout this page, we will describe how to compile the example file `example.
 --8<-- "integration/example.cpp"
 ```

+When executed, this program should create output similar to
+
+```json
+--8<-- "../../examples/meta.output"
+```
+
 ## Homebrew

 If you are using OS X and [Homebrew](http://brew.sh), just type
@ -26,11 +32,9 @@ instead. See [nlohmann-json](https://formulae.brew.sh/formula/nlohmann-json) for

 	1. Create the following file:

-		=== "example.cpp"
-
-			```cpp
-			--8<-- "integration/example.cpp"
-			```
+        ```cpp title="example.cpp"
+        --8<-- "integration/example.cpp"
+        ```

 	2. Install the package

@ -50,6 +54,8 @@ instead. See [nlohmann-json](https://formulae.brew.sh/formula/nlohmann-json) for
 		clang++ example.cpp -I/usr/local/Cellar/nlohmann-json/3.7.3/include -std=c++11 -o example
 		```

+:material-update: The [formula](https://formulae.brew.sh/formula/nlohmann-json) is updated automatically.
+
 ## Meson

 If you are using the [Meson Build System](http://mesonbuild.com), add this source tree as a [meson subproject](https://mesonbuild.com/Subprojects.html#using-a-subproject). You may also use the `include.zip` published in this project's [Releases](https://github.com/nlohmann/json/releases) to reduce the size of the vendored source tree. Alternatively, you can get a wrap file by downloading it from [Meson WrapDB](https://wrapdb.mesonbuild.com/nlohmann_json), or simply use `meson wrap install nlohmann_json`. Please see the meson project for any issues regarding the packaging.
@ -64,24 +70,17 @@ If you are using [Conan](https://www.conan.io/) to manage your dependencies, mer

 	1. Create the following files:

-		=== "Conanfile.txt"
-			
-			```ini
-			--8<-- "integration/conan/Conanfile.txt"
-			```
+        ```ini title="Conanfile.txt"
+        --8<-- "integration/conan/Conanfile.txt"
+        ```

-		=== "CMakeLists.txt"
-
-		    ```cmake
-			--8<-- "integration/conan/CMakeLists.txt"
-		    ```
-
-		=== "example.cpp"
-
-			```cpp
-			--8<-- "integration/conan/example.cpp"
-			```
+        ```cmake title="CMakeLists.txt"
+        --8<-- "integration/conan/CMakeLists.txt"
+        ```

+        ```cpp title="example.cpp"
+        --8<-- "integration/conan/example.cpp"
+        ```

 	2. Build:

@ -93,6 +92,8 @@ If you are using [Conan](https://www.conan.io/) to manage your dependencies, mer
 		cmake --build .
 		```

+:material-update: The [package](https://conan.io/center/nlohmann_json) is updated automatically.
+
 ## Spack

 If you are using [Spack](https://www.spack.io/) to manage your dependencies, you can use the [`nlohmann-json` package](https://spack.readthedocs.io/en/latest/package_list.html#nlohmann-json). Please see the [spack project](https://github.com/spack/spack) for any issues regarding the packaging.
@ -113,17 +114,13 @@ If you are using [vcpkg](https://github.com/Microsoft/vcpkg/) on your project fo

 	1. Create the following files:

-		=== "CMakeLists.txt"
-
-		    ```cmake
-			--8<-- "integration/vcpkg/CMakeLists.txt"
-		    ```
-
-		=== "example.cpp"
-
-			```cpp
-			--8<-- "integration/vcpkg/example.cpp"
-			```
+        ```cmake title="CMakeLists.txt"
+        --8<-- "integration/vcpkg/CMakeLists.txt"
+        ```
+    
+        ```cpp title="example.cpp"
+        --8<-- "integration/vcpkg/example.cpp"
+        ```

    2. Install package:

@ -146,6 +143,8 @@ If you are using [vcpkg](https://github.com/Microsoft/vcpkg/) on your project fo

 If you are using [cget](http://cget.readthedocs.io/en/latest/), you can install the latest development version with `cget install nlohmann/json`. A specific version can be installed with `cget install nlohmann/json@v3.1.0`. Also, the multiple header version can be installed by adding the `-DJSON_MultipleHeaders=ON` flag (i.e., `cget install nlohmann/json -DJSON_MultipleHeaders=ON`).

+:material-update: cget reads directly from the [GitHub repository](https://github.com/nlohmann/json) and is always up-to-date.
+
 ## CocoaPods

 If you are using [CocoaPods](https://cocoapods.org), you can use the library by adding pod `"nlohmann_json", '~>3.1.2'` to your podfile (see [an example](https://bitbucket.org/benman/nlohmann_json-cocoapod/src/master/)). Please file issues [here](https://bitbucket.org/benman/nlohmann_json-cocoapod/issues?status=new&status=open).
@ -162,19 +161,27 @@ If you are using [conda](https://conda.io/), you can use the package [nlohmann_j

 If you are using [MSYS2](http://www.msys2.org/), you can use the [mingw-w64-nlohmann-json](https://packages.msys2.org/base/mingw-w64-nlohmann-json) package, just type `pacman -S mingw-w64-i686-nlohmann-json` or `pacman -S mingw-w64-x86_64-nlohmann-json` for installation. Please file issues [here](https://github.com/msys2/MINGW-packages/issues/new?title=%5Bnlohmann-json%5D) if you experience problems with the packages.

+:material-update: The [package](https://packages.msys2.org/base/mingw-w64-nlohmann-json) is updated automatically.
+
 ## MacPorts

 If you are using [MacPorts](https://ports.macports.org), execute `sudo port install nlohmann-json` to install the [nlohmann-json](https://ports.macports.org/port/nlohmann-json/) package.

+:material-update: The [package](https://ports.macports.org/port/nlohmann-json/) is updated automatically.
+
 ## build2

-If you are using [`build2`](https://build2.org), you can use the [`nlohmann-json`](https://cppget.org/nlohmann-json) package from the public repository http://cppget.org or directly from the [package's sources repository](https://github.com/build2-packaging/nlohmann-json). In your project's `manifest` file, just add `depends: nlohmann-json` (probably with some [version constraints](https://build2.org/build2-toolchain/doc/build2-toolchain-intro.xhtml#guide-add-remove-deps)). If you are not familiar with using dependencies in `build2`, [please read this introduction](https://build2.org/build2-toolchain/doc/build2-toolchain-intro.xhtml).
+If you are using [`build2`](https://build2.org), you can use the [`nlohmann-json`](https://cppget.org/nlohmann-json) package from the public repository <http://cppget.org> or directly from the [package's sources repository](https://github.com/build2-packaging/nlohmann-json). In your project's `manifest` file, just add `depends: nlohmann-json` (probably with some [version constraints](https://build2.org/build2-toolchain/doc/build2-toolchain-intro.xhtml#guide-add-remove-deps)). If you are not familiar with using dependencies in `build2`, [please read this introduction](https://build2.org/build2-toolchain/doc/build2-toolchain-intro.xhtml).
 Please file issues [here](https://github.com/build2-packaging/nlohmann-json) if you experience problems with the packages.

+:material-update: The [package](https://cppget.org/nlohmann-json) is updated automatically.
+
 ## wsjcpp

 If you are using [`wsjcpp`](http://wsjcpp.org), you can use the command `wsjcpp install "https://github.com/nlohmann/json:develop"` to get the latest version. Note you can change the branch ":develop" to an existing tag or another branch.

+:material-update: wsjcpp reads directly from the [GitHub repository](https://github.com/nlohmann/json) and is always up-to-date.
+
 ## CPM.cmake

 If you are using [`CPM.cmake`](https://github.com/TheLartians/CPM.cmake), you can check this [`example`](https://github.com/TheLartians/CPM.cmake/tree/master/examples/json). After [adding CPM script](https://github.com/TheLartians/CPM.cmake#adding-cpm) to your project, implement the following snippet to your CMake:
--- a/include/nlohmann/detail/conversions/from_json.hpp
+++ b/include/nlohmann/detail/conversions/from_json.hpp
@ -464,7 +464,8 @@ void from_json(const BasicJsonType& j, std_fs::path& p)
 {
    if (JSON_HEDLEY_UNLIKELY(!j.is_string()))
    {
-        JSON_THROW(type_error::create(302, "type must be string, but is " + std::string(j.type_name()), j));
+        // Not tested because of #3377 (related #3070)
+        JSON_THROW(type_error::create(302, "type must be string, but is " + std::string(j.type_name()), j)); // LCOV_EXCL_LINE
    }
    p = *j.template get_ptr<const typename BasicJsonType::string_t*>();
 }
--- a/include/nlohmann/detail/iterators/iter_impl.hpp
+++ b/include/nlohmann/detail/iterators/iter_impl.hpp
@ -352,7 +352,7 @@ class iter_impl // NOLINT(cppcoreguidelines-special-member-functions,hicpp-speci
    @brief post-increment (it++)
    @pre The iterator is initialized; i.e. `m_object != nullptr`.
    */
-    iter_impl const operator++(int) // NOLINT(readability-const-return-type)
+    iter_impl operator++(int)& // NOLINT(cert-dcl21-cpp)
    {
        auto result = *this;
        ++(*this);
@ -403,7 +403,7 @@ class iter_impl // NOLINT(cppcoreguidelines-special-member-functions,hicpp-speci
    @brief post-decrement (it--)
    @pre The iterator is initialized; i.e. `m_object != nullptr`.
    */
-    iter_impl const operator--(int) // NOLINT(readability-const-return-type)
+    iter_impl operator--(int)& // NOLINT(cert-dcl21-cpp)
    {
        auto result = *this;
        --(*this);
--- a/include/nlohmann/detail/iterators/json_reverse_iterator.hpp
+++ b/include/nlohmann/detail/iterators/json_reverse_iterator.hpp
@ -48,7 +48,7 @@ class json_reverse_iterator : public std::reverse_iterator<Base>
    explicit json_reverse_iterator(const base_iterator& it) noexcept : base_iterator(it) {}

    /// post-increment (it++)
-    json_reverse_iterator const operator++(int) // NOLINT(readability-const-return-type)
+    json_reverse_iterator operator++(int)& // NOLINT(cert-dcl21-cpp)
    {
        return static_cast<json_reverse_iterator>(base_iterator::operator++(1));
    }
@ -60,7 +60,7 @@ class json_reverse_iterator : public std::reverse_iterator<Base>
    }

    /// post-decrement (it--)
-    json_reverse_iterator const operator--(int) // NOLINT(readability-const-return-type)
+    json_reverse_iterator operator--(int)& // NOLINT(cert-dcl21-cpp)
    {
        return static_cast<json_reverse_iterator>(base_iterator::operator--(1));
    }
--- a/include/nlohmann/detail/iterators/primitive_iterator.hpp
+++ b/include/nlohmann/detail/iterators/primitive_iterator.hpp
@ -87,7 +87,7 @@ class primitive_iterator_t
        return *this;
    }

-    primitive_iterator_t const operator++(int) noexcept // NOLINT(readability-const-return-type)
+    primitive_iterator_t operator++(int)& noexcept // NOLINT(cert-dcl21-cpp)
    {
        auto result = *this;
        ++m_it;
@ -100,7 +100,7 @@ class primitive_iterator_t
        return *this;
    }

-    primitive_iterator_t const operator--(int) noexcept // NOLINT(readability-const-return-type)
+    primitive_iterator_t operator--(int)& noexcept // NOLINT(cert-dcl21-cpp)
    {
        auto result = *this;
        --m_it;
--- a/include/nlohmann/detail/macro_scope.hpp
+++ b/include/nlohmann/detail/macro_scope.hpp
@ -97,6 +97,15 @@
    #define JSON_HAS_FILESYSTEM 0
 #endif

+#ifndef JSON_HAS_THREE_WAY_COMPARISON
+    #if defined(__cpp_lib_three_way_comparison) && __cpp_lib_three_way_comparison >= 201907L \
+        && defined(__cpp_impl_three_way_comparison)&& __cpp_impl_three_way_comparison >= 201907L
+        #define JSON_HAS_THREE_WAY_COMPARISON 1
+    #else
+        #define JSON_HAS_THREE_WAY_COMPARISON 0
+    #endif
+#endif
+
 // disable documentation warnings on clang
 #if defined(__clang__)
    #pragma clang diagnostic push
@ -334,6 +343,7 @@

 #define NLOHMANN_JSON_TO(v1) nlohmann_json_j[#v1] = nlohmann_json_t.v1;
 #define NLOHMANN_JSON_FROM(v1) nlohmann_json_j.at(#v1).get_to(nlohmann_json_t.v1);
+#define NLOHMANN_JSON_FROM_WITH_DEFAULT(v1) nlohmann_json_t.v1 = nlohmann_json_j.value(#v1, nlohmann_json_default_obj.v1);

 /*!
@brief macro
@ -344,6 +354,10 @@
    friend void to_json(nlohmann::json& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) } \
    friend void from_json(const nlohmann::json& nlohmann_json_j, Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM, __VA_ARGS__)) }

+#define NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT(Type, ...)  \
+    friend void to_json(nlohmann::json& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) } \
+    friend void from_json(const nlohmann::json& nlohmann_json_j, Type& nlohmann_json_t) { Type nlohmann_json_default_obj; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT, __VA_ARGS__)) }
+
 /*!
@brief macro
@def NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE
@ -353,6 +367,10 @@
    inline void to_json(nlohmann::json& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) } \
    inline void from_json(const nlohmann::json& nlohmann_json_j, Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM, __VA_ARGS__)) }

+#define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT(Type, ...)  \
+    inline void to_json(nlohmann::json& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) } \
+    inline void from_json(const nlohmann::json& nlohmann_json_j, Type& nlohmann_json_t) { Type nlohmann_json_default_obj; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT, __VA_ARGS__)) }
+

 // inspired from https://stackoverflow.com/a/26745591
 // allows to call any std function as if (e.g. with begin):
--- a/include/nlohmann/detail/macro_unscope.hpp
+++ b/include/nlohmann/detail/macro_unscope.hpp
@ -8,19 +8,23 @@
 // clean up
 #undef JSON_ASSERT
 #undef JSON_INTERNAL_CATCH
-#undef JSON_CATCH
 #undef JSON_THROW
-#undef JSON_TRY
 #undef JSON_PRIVATE_UNLESS_TESTED
-#undef JSON_HAS_CPP_11
-#undef JSON_HAS_CPP_14
-#undef JSON_HAS_CPP_17
-#undef JSON_HAS_CPP_20
-#undef JSON_HAS_FILESYSTEM
-#undef JSON_HAS_EXPERIMENTAL_FILESYSTEM
 #undef NLOHMANN_BASIC_JSON_TPL_DECLARATION
 #undef NLOHMANN_BASIC_JSON_TPL
 #undef JSON_EXPLICIT
 #undef NLOHMANN_CAN_CALL_STD_FUNC_IMPL

+#ifndef JSON_TEST_KEEP_MACROS
+    #undef JSON_CATCH
+    #undef JSON_TRY
+    #undef JSON_HAS_CPP_11
+    #undef JSON_HAS_CPP_14
+    #undef JSON_HAS_CPP_17
+    #undef JSON_HAS_CPP_20
+    #undef JSON_HAS_FILESYSTEM
+    #undef JSON_HAS_EXPERIMENTAL_FILESYSTEM
+    #undef JSON_HAS_THREE_WAY_COMPARISON
+#endif
+
 #include <nlohmann/thirdparty/hedley/hedley_undef.hpp>
--- a/include/nlohmann/detail/meta/cpp_future.hpp
+++ b/include/nlohmann/detail/meta/cpp_future.hpp
@ -147,8 +147,12 @@ struct static_const
    static constexpr T value{};
 };

-template<typename T>
-constexpr T static_const<T>::value; // NOLINT(readability-redundant-declaration)
+#ifndef JSON_HAS_CPP_17
+
+    template<typename T>
+    constexpr T static_const<T>::value; // NOLINT(readability-redundant-declaration)
+
+#endif

 }  // namespace detail
 }  // namespace nlohmann
--- a/include/nlohmann/json.hpp
+++ b/include/nlohmann/json.hpp
@ -1872,6 +1872,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
    template < typename ValueType, typename std::enable_if <
                   detail::conjunction <
                       detail::negation<std::is_pointer<ValueType>>,
+                       detail::negation<std::is_same<ValueType, std::nullptr_t>>,
                       detail::negation<std::is_same<ValueType, detail::json_ref<basic_json>>>,
                                        detail::negation<std::is_same<ValueType, typename string_t::value_type>>,
                                        detail::negation<detail::is_basic_json<ValueType>>,
--- a/include/nlohmann/ordered_map.hpp
+++ b/include/nlohmann/ordered_map.hpp
@ -30,11 +30,12 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,

    // Explicit constructors instead of `using Container::Container`
    // otherwise older compilers choke on it (GCC <= 5.5, xcode <= 9.4)
-    ordered_map(const Allocator& alloc = Allocator()) : Container{alloc} {}
+    ordered_map() noexcept(noexcept(Container())) : Container{} {}
+    explicit ordered_map(const Allocator& alloc) noexcept(noexcept(Container(alloc))) : Container{alloc} {}
    template <class It>
    ordered_map(It first, It last, const Allocator& alloc = Allocator())
        : Container{first, last, alloc} {}
-    ordered_map(std::initializer_list<T> init, const Allocator& alloc = Allocator() )
+    ordered_map(std::initializer_list<value_type> init, const Allocator& alloc = Allocator() )
        : Container{init, alloc} {}

    std::pair<iterator, bool> emplace(const key_type& key, T&& t)
--- a/single_include/nlohmann/json.hpp
+++ b/single_include/nlohmann/json.hpp
@ -2394,6 +2394,15 @@ using is_detected_convertible =
    #define JSON_HAS_FILESYSTEM 0
 #endif

+#ifndef JSON_HAS_THREE_WAY_COMPARISON
+    #if defined(__cpp_lib_three_way_comparison) && __cpp_lib_three_way_comparison >= 201907L \
+        && defined(__cpp_impl_three_way_comparison)&& __cpp_impl_three_way_comparison >= 201907L
+        #define JSON_HAS_THREE_WAY_COMPARISON 1
+    #else
+        #define JSON_HAS_THREE_WAY_COMPARISON 0
+    #endif
+#endif
+
 // disable documentation warnings on clang
 #if defined(__clang__)
    #pragma clang diagnostic push
@ -2631,6 +2640,7 @@ using is_detected_convertible =

 #define NLOHMANN_JSON_TO(v1) nlohmann_json_j[#v1] = nlohmann_json_t.v1;
 #define NLOHMANN_JSON_FROM(v1) nlohmann_json_j.at(#v1).get_to(nlohmann_json_t.v1);
+#define NLOHMANN_JSON_FROM_WITH_DEFAULT(v1) nlohmann_json_t.v1 = nlohmann_json_j.value(#v1, nlohmann_json_default_obj.v1);

 /*!
@brief macro
@ -2641,6 +2651,10 @@ using is_detected_convertible =
    friend void to_json(nlohmann::json& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) } \
    friend void from_json(const nlohmann::json& nlohmann_json_j, Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM, __VA_ARGS__)) }

+#define NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT(Type, ...)  \
+    friend void to_json(nlohmann::json& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) } \
+    friend void from_json(const nlohmann::json& nlohmann_json_j, Type& nlohmann_json_t) { Type nlohmann_json_default_obj; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT, __VA_ARGS__)) }
+
 /*!
@brief macro
@def NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE
@ -2650,6 +2664,10 @@ using is_detected_convertible =
    inline void to_json(nlohmann::json& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) } \
    inline void from_json(const nlohmann::json& nlohmann_json_j, Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM, __VA_ARGS__)) }

+#define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT(Type, ...)  \
+    inline void to_json(nlohmann::json& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) } \
+    inline void from_json(const nlohmann::json& nlohmann_json_j, Type& nlohmann_json_t) { Type nlohmann_json_default_obj; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT, __VA_ARGS__)) }
+

 // inspired from https://stackoverflow.com/a/26745591
 // allows to call any std function as if (e.g. with begin):
@ -3173,8 +3191,12 @@ struct static_const
    static constexpr T value{};
 };

-template<typename T>
-constexpr T static_const<T>::value; // NOLINT(readability-redundant-declaration)
+#ifndef JSON_HAS_CPP_17
+
+    template<typename T>
+    constexpr T static_const<T>::value; // NOLINT(readability-redundant-declaration)
+
+#endif

 }  // namespace detail
 }  // namespace nlohmann
@ -4257,7 +4279,8 @@ void from_json(const BasicJsonType& j, std_fs::path& p)
 {
    if (JSON_HEDLEY_UNLIKELY(!j.is_string()))
    {
-        JSON_THROW(type_error::create(302, "type must be string, but is " + std::string(j.type_name()), j));
+        // Not tested because of #3377 (related #3070)
+        JSON_THROW(type_error::create(302, "type must be string, but is " + std::string(j.type_name()), j)); // LCOV_EXCL_LINE
    }
    p = *j.template get_ptr<const typename BasicJsonType::string_t*>();
 }
@ -11299,7 +11322,7 @@ class primitive_iterator_t
        return *this;
    }

-    primitive_iterator_t const operator++(int) noexcept // NOLINT(readability-const-return-type)
+    primitive_iterator_t operator++(int)& noexcept // NOLINT(cert-dcl21-cpp)
    {
        auto result = *this;
        ++m_it;
@ -11312,7 +11335,7 @@ class primitive_iterator_t
        return *this;
    }

-    primitive_iterator_t const operator--(int) noexcept // NOLINT(readability-const-return-type)
+    primitive_iterator_t operator--(int)& noexcept // NOLINT(cert-dcl21-cpp)
    {
        auto result = *this;
        --m_it;
@ -11719,7 +11742,7 @@ class iter_impl // NOLINT(cppcoreguidelines-special-member-functions,hicpp-speci
    @brief post-increment (it++)
    @pre The iterator is initialized; i.e. `m_object != nullptr`.
    */
-    iter_impl const operator++(int) // NOLINT(readability-const-return-type)
+    iter_impl operator++(int)& // NOLINT(cert-dcl21-cpp)
    {
        auto result = *this;
        ++(*this);
@ -11770,7 +11793,7 @@ class iter_impl // NOLINT(cppcoreguidelines-special-member-functions,hicpp-speci
    @brief post-decrement (it--)
    @pre The iterator is initialized; i.e. `m_object != nullptr`.
    */
-    iter_impl const operator--(int) // NOLINT(readability-const-return-type)
+    iter_impl operator--(int)& // NOLINT(cert-dcl21-cpp)
    {
        auto result = *this;
        --(*this);
@ -12158,7 +12181,7 @@ class json_reverse_iterator : public std::reverse_iterator<Base>
    explicit json_reverse_iterator(const base_iterator& it) noexcept : base_iterator(it) {}

    /// post-increment (it++)
-    json_reverse_iterator const operator++(int) // NOLINT(readability-const-return-type)
+    json_reverse_iterator operator++(int)& // NOLINT(cert-dcl21-cpp)
    {
        return static_cast<json_reverse_iterator>(base_iterator::operator++(1));
    }
@ -12170,7 +12193,7 @@ class json_reverse_iterator : public std::reverse_iterator<Base>
    }

    /// post-decrement (it--)
-    json_reverse_iterator const operator--(int) // NOLINT(readability-const-return-type)
+    json_reverse_iterator operator--(int)& // NOLINT(cert-dcl21-cpp)
    {
        return static_cast<json_reverse_iterator>(base_iterator::operator--(1));
    }
@ -17057,11 +17080,12 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,

    // Explicit constructors instead of `using Container::Container`
    // otherwise older compilers choke on it (GCC <= 5.5, xcode <= 9.4)
-    ordered_map(const Allocator& alloc = Allocator()) : Container{alloc} {}
+    ordered_map() noexcept(noexcept(Container())) : Container{} {}
+    explicit ordered_map(const Allocator& alloc) noexcept(noexcept(Container(alloc))) : Container{alloc} {}
    template <class It>
    ordered_map(It first, It last, const Allocator& alloc = Allocator())
        : Container{first, last, alloc} {}
-    ordered_map(std::initializer_list<T> init, const Allocator& alloc = Allocator() )
+    ordered_map(std::initializer_list<value_type> init, const Allocator& alloc = Allocator() )
        : Container{init, alloc} {}

    std::pair<iterator, bool> emplace(const key_type& key, T&& t)
@ -19043,6 +19067,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
    template < typename ValueType, typename std::enable_if <
                   detail::conjunction <
                       detail::negation<std::is_pointer<ValueType>>,
+                       detail::negation<std::is_same<ValueType, std::nullptr_t>>,
                       detail::negation<std::is_same<ValueType, detail::json_ref<basic_json>>>,
                                        detail::negation<std::is_same<ValueType, typename string_t::value_type>>,
                                        detail::negation<detail::is_basic_json<ValueType>>,
@ -21928,21 +21953,25 @@ inline nlohmann::json::json_pointer operator "" _json_pointer(const char* s, std
 // clean up
 #undef JSON_ASSERT
 #undef JSON_INTERNAL_CATCH
-#undef JSON_CATCH
 #undef JSON_THROW
-#undef JSON_TRY
 #undef JSON_PRIVATE_UNLESS_TESTED
-#undef JSON_HAS_CPP_11
-#undef JSON_HAS_CPP_14
-#undef JSON_HAS_CPP_17
-#undef JSON_HAS_CPP_20
-#undef JSON_HAS_FILESYSTEM
-#undef JSON_HAS_EXPERIMENTAL_FILESYSTEM
 #undef NLOHMANN_BASIC_JSON_TPL_DECLARATION
 #undef NLOHMANN_BASIC_JSON_TPL
 #undef JSON_EXPLICIT
 #undef NLOHMANN_CAN_CALL_STD_FUNC_IMPL

+#ifndef JSON_TEST_KEEP_MACROS
+    #undef JSON_CATCH
+    #undef JSON_TRY
+    #undef JSON_HAS_CPP_11
+    #undef JSON_HAS_CPP_14
+    #undef JSON_HAS_CPP_17
+    #undef JSON_HAS_CPP_20
+    #undef JSON_HAS_FILESYSTEM
+    #undef JSON_HAS_EXPERIMENTAL_FILESYSTEM
+    #undef JSON_HAS_THREE_WAY_COMPARISON
+#endif
+
 // #include <nlohmann/thirdparty/hedley/hedley_undef.hpp>


--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@ -1,163 +1,131 @@
+cmake_minimum_required(VERSION 3.13)
+
 option(JSON_Valgrind    "Execute test suite with Valgrind." OFF)
 option(JSON_FastTests   "Skip expensive/slow tests." OFF)

-# download test data
-include(${CMAKE_CURRENT_SOURCE_DIR}/../cmake/download_test_data.cmake)
+set(JSON_TestStandards "" CACHE STRING "The list of standards to test explicitly.")

-# test fixture to download test data
-add_test(NAME "download_test_data" COMMAND ${CMAKE_COMMAND} --build ${CMAKE_BINARY_DIR} --target download_test_data)
-set_tests_properties(download_test_data PROPERTIES FIXTURES_SETUP TEST_DATA)
+include(test)

-if(JSON_Valgrind)
-    find_program(CMAKE_MEMORYCHECK_COMMAND valgrind)
-    message(STATUS "Executing test suite with Valgrind (${CMAKE_MEMORYCHECK_COMMAND})")
-    set(memcheck_command "${CMAKE_MEMORYCHECK_COMMAND} ${CMAKE_MEMORYCHECK_COMMAND_OPTIONS} --error-exitcode=1 --leak-check=full")
-    separate_arguments(memcheck_command)
+#############################################################################
+# override standard support
+#############################################################################
+
+# compiling json.hpp in C++14 mode fails with Clang <4.0
+if (CMAKE_CXX_COMPILER_ID STREQUAL "Clang" AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS 4.0)
+    unset(compiler_supports_cpp_14)
 endif()

-#############################################################################
-# doctest library with the main function to speed up build
-#############################################################################
-
-add_library(doctest_main OBJECT src/unit.cpp)
-set_target_properties(doctest_main PROPERTIES
-    COMPILE_DEFINITIONS "$<$<CXX_COMPILER_ID:MSVC>:_SCL_SECURE_NO_WARNINGS>"
-    COMPILE_OPTIONS "$<$<CXX_COMPILER_ID:MSVC>:/EHsc;$<$<CONFIG:Release>:/Od>>"
-)
-if (${CMAKE_VERSION} VERSION_LESS "3.8.0")
-    target_compile_features(doctest_main PUBLIC cxx_range_for)
-else()
-    target_compile_features(doctest_main PUBLIC cxx_std_11)
-endif()
-target_include_directories(doctest_main PRIVATE "thirdparty/doctest")
-
-# https://stackoverflow.com/questions/2368811/how-to-set-warning-level-in-cmake
-if(MSVC)
-    # Force to always compile with W4
-    if(CMAKE_CXX_FLAGS MATCHES "/W[0-4]")
-        string(REGEX REPLACE "/W[0-4]" "/W4" CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS}")
-    else()
-        set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /W4")
-    endif()
-
-	# Disable warning C4566: character represented by universal-character-name '\uFF01' cannot be represented in the current code page (1252)
-	# Disable warning C4996: 'nlohmann::basic_json<std::map,std::vector,std::string,bool,int64_t,uint64_t,double,std::allocator,nlohmann::adl_serializer>::operator <<': was declared deprecated
-    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /wd4566 /wd4996")
-
-	# https://github.com/nlohmann/json/issues/1114
-	set(CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS_DEBUG} /bigobj")
-endif()
-
-#############################################################################
-# one executable for each unit test file
-#############################################################################
-
-# check if compiler supports C++17
-foreach(feature ${CMAKE_CXX_COMPILE_FEATURES})
-    if (${feature} STREQUAL cxx_std_17)
-        set(compiler_supports_cpp_17 TRUE)
-    endif()
-endforeach()
 # Clang only supports C++17 starting from Clang 5.0
-if ("${CMAKE_CXX_COMPILER_ID}" MATCHES "Clang" AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS 5.0)
+if (CMAKE_CXX_COMPILER_ID STREQUAL "Clang" AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS 5.0)
    unset(compiler_supports_cpp_17)
 endif()
 # MSVC 2015 (14.0) does not support C++17
-if ("${CMAKE_CXX_COMPILER_ID}" MATCHES "MSVC" AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS 19.1)
+if (CMAKE_CXX_COMPILER_ID STREQUAL "MSVC" AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS 19.1)
    unset(compiler_supports_cpp_17)
 endif()

-file(GLOB files src/unit-*.cpp)
+# Clang C++20 support appears insufficient prior to Clang 9.0 (based on CI build failure)
+if (CMAKE_CXX_COMPILER_ID STREQUAL "Clang" AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS 9.0)
+    unset(compiler_supports_cpp_20)
+endif()
+# GCC started supporting C++20 features in 8.0 but a test for #3070 segfaults prior to 9.0
+if (CMAKE_CXX_COMPILER_ID STREQUAL "GNU" AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS 9.0)
+    unset(compiler_supports_cpp_20)
+endif()

-foreach(file ${files})
-    get_filename_component(file_basename ${file} NAME_WE)
-    string(REGEX REPLACE "unit-([^$]+)" "test-\\1" testcase ${file_basename})
+#############################################################################
+# test_main library with shared code to speed up build and common settings
+#############################################################################

-    add_executable(${testcase} $<TARGET_OBJECTS:doctest_main> ${file})
-    target_compile_definitions(${testcase} PRIVATE DOCTEST_CONFIG_SUPER_FAST_ASSERTS)
-    target_compile_options(${testcase} PRIVATE
-        $<$<CXX_COMPILER_ID:MSVC>:/EHsc;$<$<CONFIG:Release>:/Od>>
-        $<$<NOT:$<CXX_COMPILER_ID:MSVC>>:-Wno-deprecated;-Wno-float-equal>
-        $<$<CXX_COMPILER_ID:GNU>:-Wno-deprecated-declarations>
-    )
-    target_include_directories(${testcase} PRIVATE ${CMAKE_BINARY_DIR}/include thirdparty/doctest thirdparty/fifo_map)
-    target_link_libraries(${testcase} PRIVATE ${NLOHMANN_JSON_TARGET_NAME})
+add_library(test_main OBJECT src/unit.cpp)
+target_compile_definitions(test_main PUBLIC
+    DOCTEST_CONFIG_SUPER_FAST_ASSERTS
+    JSON_TEST_KEEP_MACROS
+)
+target_compile_features(test_main PRIVATE cxx_std_11)
+target_compile_options(test_main PUBLIC
+    $<$<CXX_COMPILER_ID:MSVC>:/EHsc;$<$<CONFIG:Release>:/Od>>
+    # MSVC: Force to always compile with W4
+    #       Disable warning C4566: character represented by universal-character-name '\uFF01'
+    #                              cannot be represented in the current code page (1252)
+    #       Disable warning C4996: 'nlohmann::basic_json<...>::operator <<': was declared deprecated
+    $<$<CXX_COMPILER_ID:MSVC>:/W4 /wd4566 /wd4996>
+    # https://github.com/nlohmann/json/issues/1114
+    $<$<CXX_COMPILER_ID:MSVC>:/bigobj> $<$<BOOL:${MINGW}>:-Wa,-mbig-obj>

-    # add a copy with C++17 compilation
-    if (compiler_supports_cpp_17)
-        file(READ ${file} FILE_CONTENT)
-        string(FIND "${FILE_CONTENT}" "JSON_HAS_CPP_17" CPP_17_FOUND)
-        if(NOT ${CPP_17_FOUND} EQUAL -1)
-            add_executable(${testcase}_cpp17 $<TARGET_OBJECTS:doctest_main> ${file})
-            target_compile_definitions(${testcase}_cpp17 PRIVATE DOCTEST_CONFIG_SUPER_FAST_ASSERTS)
-            target_compile_options(${testcase}_cpp17 PRIVATE
-                $<$<CXX_COMPILER_ID:MSVC>:/EHsc;$<$<CONFIG:Release>:/Od>>
-                $<$<NOT:$<CXX_COMPILER_ID:MSVC>>:-Wno-deprecated;-Wno-float-equal>
-                $<$<CXX_COMPILER_ID:GNU>:-Wno-deprecated-declarations>
-            )
-            target_include_directories(${testcase}_cpp17 PRIVATE ${CMAKE_BINARY_DIR}/include thirdparty/doctest thirdparty/fifo_map)
-            target_link_libraries(${testcase}_cpp17 PRIVATE ${NLOHMANN_JSON_TARGET_NAME})
-            target_compile_features(${testcase}_cpp17 PRIVATE cxx_std_17)
+    $<$<NOT:$<CXX_COMPILER_ID:MSVC>>:-Wno-deprecated;-Wno-float-equal>
+    $<$<CXX_COMPILER_ID:GNU>:-Wno-deprecated-declarations>
+)
+target_include_directories(test_main PUBLIC
+    thirdparty/doctest
+    thirdparty/fifo_map
+    ${PROJECT_BINARY_DIR}/include
+)
+target_link_libraries(test_main PUBLIC ${NLOHMANN_JSON_TARGET_NAME})

-            if (CMAKE_CXX_COMPILER_ID STREQUAL "GNU" AND CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL 8.0 AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS 9.0 AND NOT MINGW)
-                # fix for https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90050
-                target_link_libraries(${testcase}_cpp17 PRIVATE stdc++fs)
-            endif()
+#############################################################################
+# define test- and standard-specific build settings
+#############################################################################

-            if (JSON_FastTests)
-                add_test(NAME "${testcase}_cpp17"
-                    COMMAND ${testcase}_cpp17 ${DOCTEST_TEST_FILTER}
-                    WORKING_DIRECTORY ${CMAKE_SOURCE_DIR}
-                )
-            else()
-                add_test(NAME "${testcase}_cpp17"
-                    COMMAND ${testcase}_cpp17 ${DOCTEST_TEST_FILTER} --no-skip
-                    WORKING_DIRECTORY ${CMAKE_SOURCE_DIR}
-                )
-            endif()
-            set_tests_properties("${testcase}_cpp17" PROPERTIES LABELS "all" FIXTURES_REQUIRED TEST_DATA)
-        endif()
-    endif()
+if (CMAKE_CXX_COMPILER_ID STREQUAL "GNU"
+    AND CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL 8.0
+    AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS 9.0 AND NOT MINGW)
+    # fix for https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90050
+    json_test_set_test_options(all CXX_STANDARDS 17 LINK_LIBRARIES stdc++fs)
+endif()

-    if (JSON_FastTests)
-        add_test(NAME "${testcase}"
-            COMMAND ${testcase} ${DOCTEST_TEST_FILTER}
-            WORKING_DIRECTORY ${CMAKE_SOURCE_DIR}
-        )
-    else()
-        add_test(NAME "${testcase}"
-            COMMAND ${testcase} ${DOCTEST_TEST_FILTER} --no-skip
-            WORKING_DIRECTORY ${CMAKE_SOURCE_DIR}
-        )
-    endif()
-    set_tests_properties("${testcase}" PROPERTIES LABELS "all" FIXTURES_REQUIRED TEST_DATA)
-
-    if(JSON_Valgrind)
-        add_test(NAME "${testcase}_valgrind"
-            COMMAND ${memcheck_command} ${CMAKE_CURRENT_BINARY_DIR}/${testcase} ${DOCTEST_TEST_FILTER}
-            WORKING_DIRECTORY ${CMAKE_SOURCE_DIR}
-        )
-        set_tests_properties("${testcase}_valgrind" PROPERTIES LABELS "valgrind" FIXTURES_REQUIRED TEST_DATA)
-    endif()
-endforeach()
+if (CMAKE_CXX_COMPILER_ID STREQUAL "MSVC")
+    # avoid stack overflow, see https://github.com/nlohmann/json/issues/2955
+    json_test_set_test_options("test-cbor;test-msgpack;test-ubjson" LINK_OPTIONS /STACK:4000000)
+endif()

 # disable exceptions for test-disabled_exceptions
-target_compile_definitions(test-disabled_exceptions PUBLIC JSON_NOEXCEPTION)
+json_test_set_test_options(test-disabled_exceptions COMPILE_DEFINITIONS JSON_NOEXCEPTION)
 if (CMAKE_CXX_COMPILER_ID STREQUAL "Clang" OR CMAKE_CXX_COMPILER_ID STREQUAL "AppleClang" OR CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
-    target_compile_options(test-disabled_exceptions PUBLIC -fno-exceptions)
+json_test_set_test_options(test-disabled_exceptions COMPILE_OPTIONS -fno-exceptions)
 elseif (CMAKE_CXX_COMPILER_ID STREQUAL "MSVC")
    # disabled due to https://github.com/nlohmann/json/discussions/2824
-    #target_compile_options(test-disabled_exceptions PUBLIC /EH)
-    #target_compile_definitions(test-disabled_exceptions PUBLIC _HAS_EXCEPTIONS=0)
+    #json_test_set_test_options(test-disabled_exceptions COMPILE_DEFINITIONS _HAS_EXCEPTIONS=0 COMPILE_OPTIONS /EH)
 endif()

-# avoid stack overflow, see https://github.com/nlohmann/json/issues/2955
-if (CMAKE_CXX_COMPILER_ID STREQUAL "MSVC")
-    set_property(TARGET test-cbor APPEND_STRING PROPERTY LINK_FLAGS " /STACK:4000000")
-    set_property(TARGET test-msgpack APPEND_STRING PROPERTY LINK_FLAGS " /STACK:4000000")
-    set_property(TARGET test-ubjson APPEND_STRING PROPERTY LINK_FLAGS " /STACK:4000000")
+#############################################################################
+# add unit tests
+#############################################################################
+
+if("${JSON_TestStandards}" STREQUAL "")
+    set(test_cxx_standards 11 14 17 20 23)
+    unset(test_force)
+else()
+    set(test_cxx_standards ${JSON_TestStandards})
+    set(test_force FORCE)
 endif()

+# Print selected standards marking unavailable ones with brackets
+set(msg_standards "")
+foreach(cxx_standard ${test_cxx_standards})
+    if(compiler_supports_cpp_${cxx_standard})
+        list(APPEND msg_standards ${cxx_standard})
+    else()
+        list(APPEND msg_standards [${cxx_standard}])
+    endif()
+endforeach()
+string(JOIN " " msg_standards ${msg_standards})
+set(msg "Testing standards: ${msg_standards}")
+if(test_force)
+    string(APPEND msg " (forced)")
+endif()
+message(STATUS "${msg}")
+
+# *DO* use json_test_set_test_options() above this line
+
+file(GLOB files src/unit-*.cpp)
+foreach(file ${files})
+    json_test_add_test_for(${file} MAIN test_main CXX_STANDARDS ${test_cxx_standards} ${test_force})
+endforeach()
+
+# *DO NOT* use json_test_set_test_options() below this line
+
 #############################################################################
 # Test the generated build configs
 #############################################################################
@ -170,4 +138,5 @@ endif()

 add_subdirectory(cmake_add_subdirectory)
 add_subdirectory(cmake_fetch_content)
+add_subdirectory(cmake_fetch_content2)
 add_subdirectory(cmake_target_include_directories)
--- a/test/cmake_fetch_content2/CMakeLists.txt
+++ b/test/cmake_fetch_content2/CMakeLists.txt
@ -0,0 +1,20 @@
+if (${CMAKE_VERSION} VERSION_GREATER "3.14.0")
+  add_test(NAME cmake_fetch_content2_configure
+    COMMAND ${CMAKE_COMMAND}
+    -G "${CMAKE_GENERATOR}"
+    -DCMAKE_CXX_COMPILER=${CMAKE_CXX_COMPILER}
+    -Dnlohmann_json_source=${PROJECT_SOURCE_DIR}
+    ${CMAKE_CURRENT_SOURCE_DIR}/project
+  )
+  add_test(NAME cmake_fetch_content2_build
+    COMMAND ${CMAKE_COMMAND} --build .
+  )
+  set_tests_properties(cmake_fetch_content2_configure PROPERTIES
+    FIXTURES_SETUP cmake_fetch_content2
+    LABELS "git_required;not_reproducible"
+  )
+  set_tests_properties(cmake_fetch_content2_build PROPERTIES
+    FIXTURES_REQUIRED cmake_fetch_content2
+    LABELS "git_required;not_reproducible"
+  )
+endif()
--- a/test/cmake_fetch_content2/project/CMakeLists.txt
+++ b/test/cmake_fetch_content2/project/CMakeLists.txt
@ -0,0 +1,15 @@
+cmake_minimum_required(VERSION 3.14)
+
+project(DummyImport CXX)
+
+include(FetchContent)
+
+get_filename_component(GIT_REPOSITORY_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}/../../.. ABSOLUTE)
+FetchContent_Declare(json GIT_REPOSITORY ${GIT_REPOSITORY_DIRECTORY} GIT_TAG HEAD)
+FetchContent_MakeAvailable(json)
+
+add_executable(with_namespace_target main.cpp)
+target_link_libraries(with_namespace_target nlohmann_json::nlohmann_json)
+
+add_executable(without_namespace_target main.cpp)
+target_link_libraries(without_namespace_target nlohmann_json)
--- a/test/cmake_fetch_content2/project/main.cpp
+++ b/test/cmake_fetch_content2/project/main.cpp
@ -0,0 +1,8 @@
+#include <nlohmann/json.hpp>
+
+int main(int argc, char **argv)
+{
+    nlohmann::json j;
+
+    return 0;
+}
--- a/test/src/unit-allocator.cpp
+++ b/test/src/unit-allocator.cpp
@ -39,6 +39,8 @@ namespace
 template<class T>
 struct bad_allocator : std::allocator<T>
 {
+    using std::allocator<T>::allocator;
+
    template<class... Args>
    void construct(T* /*unused*/, Args&& ... /*unused*/)
    {
--- a/test/src/unit-alt-string.cpp
+++ b/test/src/unit-alt-string.cpp
@ -37,7 +37,7 @@ SOFTWARE.

 /* forward declarations */
 class alt_string;
-bool operator<(const char* op1, const alt_string& op2);
+bool operator<(const char* op1, const alt_string& op2) noexcept;
 void int_to_string(alt_string& target, std::size_t value);

 /*
@ -104,12 +104,12 @@ class alt_string
    }

    template <typename op_type>
-    bool operator<(const op_type& op) const
+    bool operator<(const op_type& op) const noexcept
    {
        return str_impl < op;
    }

-    bool operator<(const alt_string& op) const
+    bool operator<(const alt_string& op) const noexcept
    {
        return str_impl < op.str_impl;
    }
@ -152,7 +152,7 @@ class alt_string
  private:
    std::string str_impl {};

-    friend bool ::operator<(const char* /*op1*/, const alt_string& /*op2*/);
+    friend bool ::operator<(const char* /*op1*/, const alt_string& /*op2*/) noexcept;
 };

 void int_to_string(alt_string& target, std::size_t value)
@ -172,7 +172,7 @@ using alt_json = nlohmann::basic_json <
                 nlohmann::adl_serializer >;


-bool operator<(const char* op1, const alt_string& op2)
+bool operator<(const char* op1, const alt_string& op2) noexcept
 {
    return op1 < op2.str_impl;
 }
--- a/test/src/unit-cbor.cpp
+++ b/test/src/unit-cbor.cpp
@ -1609,7 +1609,7 @@ TEST_CASE("CBOR")

                // callback to set binary_seen to true if a binary value was seen
                bool binary_seen = false;
-                auto callback = [&binary_seen](int /*depth*/, json::parse_event_t /*event*/, json & parsed)
+                auto callback = [&binary_seen](int /*depth*/, json::parse_event_t /*event*/, json & parsed) noexcept
                {
                    if (parsed.is_binary())
                    {
--- a/test/src/unit-class_iterator.cpp
+++ b/test/src/unit-class_iterator.cpp
@ -33,6 +33,12 @@ SOFTWARE.
 #include <nlohmann/json.hpp>
 using nlohmann::json;

+template<typename Iter>
+using can_post_increment_temporary = decltype((std::declval<Iter>()++)++);
+
+template<typename Iter>
+using can_post_decrement_temporary = decltype((std::declval<Iter>()--)--);
+
 TEST_CASE("iterator class")
 {
    SECTION("construction")
@ -399,4 +405,89 @@ TEST_CASE("iterator class")
            }
        }
    }
+    SECTION("equality-preserving")
+    {
+        SECTION("post-increment")
+        {
+            SECTION("primitive_iterator_t")
+            {
+                using Iter = nlohmann::detail::primitive_iterator_t;
+                CHECK(std::is_same < decltype(std::declval<Iter&>()++), Iter >::value);
+            }
+            SECTION("iter_impl")
+            {
+                using Iter = nlohmann::detail::iter_impl<json>;
+                CHECK(std::is_same < decltype(std::declval<Iter&>()++), Iter >::value);
+            }
+            SECTION("json_reverse_iterator")
+            {
+                using Base = nlohmann::detail::iter_impl<json>;
+                using Iter = nlohmann::detail::json_reverse_iterator<Base>;
+                CHECK(std::is_same < decltype(std::declval<Iter&>()++), Iter >::value);
+            }
+        }
+        SECTION("post-decrement")
+        {
+            SECTION("primitive_iterator_t")
+            {
+                using Iter = nlohmann::detail::primitive_iterator_t;
+                CHECK(std::is_same < decltype(std::declval<Iter&>()--), Iter >::value);
+            }
+            SECTION("iter_impl")
+            {
+                using Iter = nlohmann::detail::iter_impl<json>;
+                CHECK(std::is_same < decltype(std::declval<Iter&>()--), Iter >::value );
+            }
+            SECTION("json_reverse_iterator")
+            {
+                using Base = nlohmann::detail::iter_impl<json>;
+                using Iter = nlohmann::detail::json_reverse_iterator<Base>;
+                CHECK(std::is_same < decltype(std::declval<Iter&>()--), Iter >::value );
+            }
+        }
+    }
+    // prevent "accidental mutation of a temporary object"
+    SECTION("cert-dcl21-cpp")
+    {
+        using nlohmann::detail::is_detected;
+        SECTION("post-increment")
+        {
+            SECTION("primitive_iterator_t")
+            {
+                using Iter = nlohmann::detail::primitive_iterator_t;
+                CHECK_FALSE(is_detected<can_post_increment_temporary, Iter&>::value);
+            }
+            SECTION("iter_impl")
+            {
+                using Iter = nlohmann::detail::iter_impl<json>;
+                CHECK_FALSE(is_detected<can_post_increment_temporary, Iter&>::value);
+            }
+            SECTION("json_reverse_iterator")
+            {
+                using Base = nlohmann::detail::iter_impl<json>;
+                using Iter = nlohmann::detail::json_reverse_iterator<Base>;
+                CHECK_FALSE(is_detected<can_post_increment_temporary, Iter&>::value);
+            }
+        }
+        SECTION("post-decrement")
+        {
+            SECTION("primitive_iterator_t")
+            {
+                using Iter = nlohmann::detail::primitive_iterator_t;
+                CHECK_FALSE(is_detected<can_post_decrement_temporary, Iter&>::value);
+            }
+            SECTION("iter_impl")
+            {
+                using Iter = nlohmann::detail::iter_impl<json>;
+                CHECK_FALSE(is_detected<can_post_decrement_temporary, Iter&>::value);
+            }
+            SECTION("json_reverse_iterator")
+            {
+                using Base = nlohmann::detail::iter_impl<json>;
+                using Iter = nlohmann::detail::json_reverse_iterator<Base>;
+                CHECK_FALSE(is_detected<can_post_decrement_temporary, Iter&>::value);
+            }
+
+        }
+    }
 }
--- a/test/src/unit-class_parser.cpp
+++ b/test/src/unit-class_parser.cpp
@ -267,7 +267,7 @@ bool accept_helper(const std::string& s)
    CHECK(json::parser(nlohmann::detail::input_adapter(s)).accept(false) == !el.errored);

    // 5. parse with simple callback
-    json::parser_callback_t cb = [](int /*unused*/, json::parse_event_t /*unused*/, json& /*unused*/)
+    json::parser_callback_t cb = [](int /*unused*/, json::parse_event_t /*unused*/, json& /*unused*/) noexcept
    {
        return true;
    };
@ -1499,7 +1499,7 @@ TEST_CASE("parser class")

        // test case to make sure the callback is properly evaluated after reading a key
        {
-            json::parser_callback_t cb = [](int /*unused*/, json::parse_event_t event, json& /*unused*/)
+            json::parser_callback_t cb = [](int /*unused*/, json::parse_event_t event, json& /*unused*/) noexcept
            {
                return event != json::parse_event_t::key;
            };
@ -1538,14 +1538,14 @@ TEST_CASE("parser class")

        SECTION("filter nothing")
        {
-            json j_object = json::parse(s_object, [](int /*unused*/, json::parse_event_t /*unused*/, const json& /*unused*/)
+            json j_object = json::parse(s_object, [](int /*unused*/, json::parse_event_t /*unused*/, const json& /*unused*/) noexcept
            {
                return true;
            });

            CHECK (j_object == json({{"foo", 2}, {"bar", {{"baz", 1}}}}));

-            json j_array = json::parse(s_array, [](int /*unused*/, json::parse_event_t /*unused*/, const json& /*unused*/)
+            json j_array = json::parse(s_array, [](int /*unused*/, json::parse_event_t /*unused*/, const json& /*unused*/) noexcept
            {
                return true;
            });
@ -1555,7 +1555,7 @@ TEST_CASE("parser class")

        SECTION("filter everything")
        {
-            json j_object = json::parse(s_object, [](int /*unused*/, json::parse_event_t /*unused*/, const json& /*unused*/)
+            json j_object = json::parse(s_object, [](int /*unused*/, json::parse_event_t /*unused*/, const json& /*unused*/) noexcept
            {
                return false;
            });
@ -1563,7 +1563,7 @@ TEST_CASE("parser class")
            // the top-level object will be discarded, leaving a null
            CHECK (j_object.is_null());

-            json j_array = json::parse(s_array, [](int /*unused*/, json::parse_event_t /*unused*/, const json& /*unused*/)
+            json j_array = json::parse(s_array, [](int /*unused*/, json::parse_event_t /*unused*/, const json& /*unused*/) noexcept
            {
                return false;
            });
@ -1574,7 +1574,7 @@ TEST_CASE("parser class")

        SECTION("filter specific element")
        {
-            json j_object = json::parse(s_object, [](int /*unused*/, json::parse_event_t /*unused*/, const json & j)
+            json j_object = json::parse(s_object, [](int /*unused*/, json::parse_event_t /*unused*/, const json & j) noexcept
            {
                // filter all number(2) elements
                return j != json(2);
@ -1582,7 +1582,7 @@ TEST_CASE("parser class")

            CHECK (j_object == json({{"bar", {{"baz", 1}}}}));

-            json j_array = json::parse(s_array, [](int /*unused*/, json::parse_event_t /*unused*/, const json & j)
+            json j_array = json::parse(s_array, [](int /*unused*/, json::parse_event_t /*unused*/, const json & j) noexcept
            {
                return j != json(2);
            });
@ -1601,7 +1601,7 @@ TEST_CASE("parser class")
            CHECK (j_filtered1.size() == 2);
            CHECK (j_filtered1 == json({1, {{"qux", "baz"}}}));

-            json j_filtered2 = json::parse(structured_array, [](int /*unused*/, json::parse_event_t e, const json& /*parsed*/)
+            json j_filtered2 = json::parse(structured_array, [](int /*unused*/, json::parse_event_t e, const json& /*parsed*/) noexcept
            {
                return e != json::parse_event_t::object_end;
            });
@ -1616,7 +1616,7 @@ TEST_CASE("parser class")
            SECTION("first closing event")
            {
                {
-                    json j_object = json::parse(s_object, [](int /*unused*/, json::parse_event_t e, const json& /*unused*/)
+                    json j_object = json::parse(s_object, [](int /*unused*/, json::parse_event_t e, const json& /*unused*/) noexcept
                    {
                        static bool first = true;
                        if (e == json::parse_event_t::object_end && first)
@ -1633,7 +1633,7 @@ TEST_CASE("parser class")
                }

                {
-                    json j_array = json::parse(s_array, [](int /*unused*/, json::parse_event_t e, const json& /*unused*/)
+                    json j_array = json::parse(s_array, [](int /*unused*/, json::parse_event_t e, const json& /*unused*/) noexcept
                    {
                        static bool first = true;
                        if (e == json::parse_event_t::array_end && first)
@ -1657,13 +1657,13 @@ TEST_CASE("parser class")
            // object and array is discarded only after the closing character
            // has been read

-            json j_empty_object = json::parse("{}", [](int /*unused*/, json::parse_event_t e, const json& /*unused*/)
+            json j_empty_object = json::parse("{}", [](int /*unused*/, json::parse_event_t e, const json& /*unused*/) noexcept
            {
                return e != json::parse_event_t::object_end;
            });
            CHECK(j_empty_object == json());

-            json j_empty_array = json::parse("[]", [](int /*unused*/, json::parse_event_t e, const json& /*unused*/)
+            json j_empty_array = json::parse("[]", [](int /*unused*/, json::parse_event_t e, const json& /*unused*/) noexcept
            {
                return e != json::parse_event_t::array_end;
            });
@ -1731,7 +1731,7 @@ TEST_CASE("parser class")
    {
        SECTION("parser with callback")
        {
-            json::parser_callback_t cb = [](int /*unused*/, json::parse_event_t /*unused*/, json& /*unused*/)
+            json::parser_callback_t cb = [](int /*unused*/, json::parse_event_t /*unused*/, json& /*unused*/) noexcept
            {
                return true;
            };
--- a/test/src/unit-comparison.cpp
+++ b/test/src/unit-comparison.cpp
@ -205,6 +205,14 @@ TEST_CASE("lexicographical comparison operators")
            {
                for (size_t j = 0; j < j_values.size(); ++j)
                {
+                    // Skip comparing indicies 12 and 13, and 13 and 12 in C++20 pending fix
+                    // See issue #3207
+#if defined(JSON_HAS_CPP_20) || JSON_HAS_THREE_WAY_COMPARISON
+                    if ((i == 12 && j == 13) || (i == 13 && j == 12))
+                    {
+                        continue;
+                    }
+#endif
                    CAPTURE(i)
                    CAPTURE(j)
                    CAPTURE(j_values[i])
--- a/test/src/unit-conversions.cpp
+++ b/test/src/unit-conversions.cpp
@ -41,13 +41,6 @@ using nlohmann::json;
 #include <unordered_set>
 #include <valarray>

-#if (defined(__cplusplus) && __cplusplus >= 201703L) || (defined(_HAS_CXX17) && _HAS_CXX17 == 1) // fix for issue #464
-    #define JSON_HAS_CPP_17
-    #define JSON_HAS_CPP_14
-#elif (defined(__cplusplus) && __cplusplus >= 201402L) || (defined(_HAS_CXX14) && _HAS_CXX14 == 1)
-    #define JSON_HAS_CPP_14
-#endif
-
 // NLOHMANN_JSON_SERIALIZE_ENUM uses a static std::pair
 DOCTEST_CLANG_SUPPRESS_WARNING_PUSH
 DOCTEST_CLANG_SUPPRESS_WARNING("-Wexit-time-destructors")
--- a/test/src/unit-items.cpp
+++ b/test/src/unit-items.cpp
@ -32,13 +32,6 @@ SOFTWARE.
 #include <nlohmann/json.hpp>
 using nlohmann::json;

-#if (defined(__cplusplus) && __cplusplus >= 201703L) || (defined(_HAS_CXX17) && _HAS_CXX17 == 1) // fix for issue #464
-    #define JSON_HAS_CPP_17
-    #define JSON_HAS_CPP_14
-#elif (defined(__cplusplus) && __cplusplus >= 201402L) || (defined(_HAS_CXX14) && _HAS_CXX14 == 1)
-    #define JSON_HAS_CPP_14
-#endif
-
 // This test suite uses range for loops where values are copied. This is inefficient in usual code, but required to achieve 100% coverage.
 DOCTEST_GCC_SUPPRESS_WARNING_PUSH
 DOCTEST_GCC_SUPPRESS_WARNING("-Wrange-loop-construct")
--- a/test/src/unit-regression1.cpp
+++ b/test/src/unit-regression1.cpp
@ -42,10 +42,6 @@ using nlohmann::json;
 #include <cstdio>
 #include <test_data.hpp>

-#if (defined(__cplusplus) && __cplusplus >= 201703L) || (defined(_HAS_CXX17) && _HAS_CXX17 == 1) // fix for issue #464
-    #define JSON_HAS_CPP_17
-#endif
-
 #ifdef JSON_HAS_CPP_17
    #include <variant>
 #endif
--- a/test/src/unit-regression2.cpp
+++ b/test/src/unit-regression2.cpp
@ -42,70 +42,8 @@ using ordered_json = nlohmann::ordered_json;
 #include <type_traits>
 #include <utility>

-#if (defined(__cplusplus) && __cplusplus >= 201703L) || (defined(_HAS_CXX17) && _HAS_CXX17 == 1)  // fix for issue #464
-    #define JSON_HAS_CPP_17
-#endif
-
 #ifdef JSON_HAS_CPP_17
    #include <variant>
-
-    #if !defined(JSON_HAS_FILESYSTEM) && !defined(JSON_HAS_EXPERIMENTAL_FILESYSTEM)
-        #if defined(__cpp_lib_filesystem)
-            #define JSON_HAS_FILESYSTEM 1
-        #elif defined(__cpp_lib_experimental_filesystem)
-            #define JSON_HAS_EXPERIMENTAL_FILESYSTEM 1
-        #elif !defined(__has_include)
-            #define JSON_HAS_EXPERIMENTAL_FILESYSTEM 1
-        #elif __has_include(<filesystem>)
-            #define JSON_HAS_FILESYSTEM 1
-        #elif __has_include(<experimental/filesystem>)
-            #define JSON_HAS_EXPERIMENTAL_FILESYSTEM 1
-        #endif
-
-        // std::filesystem does not work on MinGW GCC 8: https://sourceforge.net/p/mingw-w64/bugs/737/
-        #if defined(__MINGW32__) && defined(__GNUC__) && __GNUC__ == 8
-            #undef JSON_HAS_FILESYSTEM
-            #undef JSON_HAS_EXPERIMENTAL_FILESYSTEM
-        #endif
-
-        // no filesystem support before GCC 8: https://en.cppreference.com/w/cpp/compiler_support
-        #if defined(__GNUC__) && __GNUC__ < 8 && !defined(__clang__)
-            #undef JSON_HAS_FILESYSTEM
-            #undef JSON_HAS_EXPERIMENTAL_FILESYSTEM
-        #endif
-
-        // no filesystem support before Clang 7: https://en.cppreference.com/w/cpp/compiler_support
-        #if defined(__clang_major__) && __clang_major__ < 7
-            #undef JSON_HAS_FILESYSTEM
-            #undef JSON_HAS_EXPERIMENTAL_FILESYSTEM
-        #endif
-
-        // no filesystem support before MSVC 19.14: https://en.cppreference.com/w/cpp/compiler_support
-        #if defined(_MSC_VER) && _MSC_VER < 1940
-            #undef JSON_HAS_FILESYSTEM
-            #undef JSON_HAS_EXPERIMENTAL_FILESYSTEM
-        #endif
-
-        // no filesystem support before iOS 13
-        #if defined(__IPHONE_OS_VERSION_MIN_REQUIRED) && __IPHONE_OS_VERSION_MIN_REQUIRED < 130000
-            #undef JSON_HAS_FILESYSTEM
-            #undef JSON_HAS_EXPERIMENTAL_FILESYSTEM
-        #endif
-
-        // no filesystem support before macOS Catalina
-        #if defined(__MAC_OS_X_VERSION_MIN_REQUIRED) && __MAC_OS_X_VERSION_MIN_REQUIRED < 101500
-            #undef JSON_HAS_FILESYSTEM
-            #undef JSON_HAS_EXPERIMENTAL_FILESYSTEM
-        #endif
-    #endif
-#endif
-
-#ifndef JSON_HAS_EXPERIMENTAL_FILESYSTEM
-    #define JSON_HAS_EXPERIMENTAL_FILESYSTEM 0
-#endif
-
-#ifndef JSON_HAS_FILESYSTEM
-    #define JSON_HAS_FILESYSTEM 0
 #endif

 #if JSON_HAS_EXPERIMENTAL_FILESYSTEM
@ -271,7 +209,10 @@ std::string* sax_no_exception::error_string = nullptr;

 template<class T>
 class my_allocator : public std::allocator<T>
-{};
+{
+  public:
+    using std::allocator<T>::allocator;
+};

 /////////////////////////////////////////////////////////////////////
 // for #3077
@ -338,7 +279,7 @@ TEST_CASE("regression tests 2")
               ]
             })";

-        json::parser_callback_t cb = [&](int /*level*/, json::parse_event_t event, json & parsed)
+        json::parser_callback_t cb = [&](int /*level*/, json::parse_event_t event, json & parsed) noexcept
        {
            // skip uninteresting events
            if (event == json::parse_event_t::value && !parsed.is_primitive())
@ -653,7 +594,7 @@ TEST_CASE("regression tests 2")
 #ifdef JSON_HAS_CPP_20
    SECTION("issue #2546 - parsing containers of std::byte")
    {
-        const char DATA[] = R"("Hello, world!")";
+        const char DATA[] = R"("Hello, world!")"; // NOLINT(cppcoreguidelines-avoid-c-arrays,hicpp-avoid-c-arrays,modernize-avoid-c-arrays)
        const auto s = std::as_bytes(std::span(DATA));
        json j = json::parse(s);
        CHECK(j.dump() == "\"Hello, world!\"");
@ -807,7 +748,8 @@ TEST_CASE("regression tests 2")
        const auto j_path = j.get<nlohmann::detail::std_fs::path>();
        CHECK(j_path == text_path);

-        CHECK_THROWS_WITH_AS(nlohmann::detail::std_fs::path(json(1)), "[json.exception.type_error.302] type must be string, but is number", json::type_error);
+        // Disabled pending resolution of #3377
+        // CHECK_THROWS_WITH_AS(nlohmann::detail::std_fs::path(json(1)), "[json.exception.type_error.302] type must be string, but is number", json::type_error);
    }
 #endif

@ -835,6 +777,18 @@ TEST_CASE("regression tests 2")

        CHECK(j.dump() == "[1,4]");
    }
+
+    SECTION("issue #3343 - json and ordered_json are not interchangable")
+    {
+        json::object_t jobj({ { "product", "one" } });
+        ordered_json::object_t ojobj({{"product", "one"}});
+
+        auto jit = jobj.begin();
+        auto ojit = ojobj.begin();
+
+        CHECK(jit->first == ojit->first);
+        CHECK(jit->second.get<std::string>() == ojit->second.get<std::string>());
+    }
 }

 DOCTEST_CLANG_SUPPRESS_WARNING_POP
--- a/test/src/unit-ubjson.cpp
+++ b/test/src/unit-ubjson.cpp
@ -1610,7 +1610,7 @@ TEST_CASE("UBJSON")
                CHECK_THROWS_AS(_ = json::from_ubjson(v_ubjson), json::out_of_range&);

                json j;
-                nlohmann::detail::json_sax_dom_callback_parser<json> scp(j, [](int /*unused*/, json::parse_event_t /*unused*/, const json& /*unused*/)
+                nlohmann::detail::json_sax_dom_callback_parser<json> scp(j, [](int /*unused*/, json::parse_event_t /*unused*/, const json& /*unused*/) noexcept
                {
                    return true;
                });
@ -1624,7 +1624,7 @@ TEST_CASE("UBJSON")
                CHECK_THROWS_AS(_ = json::from_ubjson(v_ubjson), json::out_of_range&);

                json j;
-                nlohmann::detail::json_sax_dom_callback_parser<json> scp(j, [](int /*unused*/, json::parse_event_t /*unused*/, const json& /*unused*/)
+                nlohmann::detail::json_sax_dom_callback_parser<json> scp(j, [](int /*unused*/, json::parse_event_t /*unused*/, const json& /*unused*/) noexcept
                {
                    return true;
                });
--- a/test/src/unit-udt_macro.cpp
+++ b/test/src/unit-udt_macro.cpp
@ -59,6 +59,42 @@ class person_with_private_data
    NLOHMANN_DEFINE_TYPE_INTRUSIVE(person_with_private_data, age, name, metadata)
 };

+class person_with_private_data_2
+{
+  private:
+    std::string name{};
+    int age = 0;
+    json metadata = nullptr;
+
+  public:
+    bool operator==(const person_with_private_data_2& rhs) const
+    {
+        return name == rhs.name && age == rhs.age && metadata == rhs.metadata;
+    }
+
+    person_with_private_data_2() = default;
+    person_with_private_data_2(std::string name_, int age_, json metadata_)
+        : name(std::move(name_))
+        , age(age_)
+        , metadata(std::move(metadata_))
+    {}
+
+    std::string getName() const
+    {
+        return name;
+    }
+    int getAge() const
+    {
+        return age;
+    }
+    json getMetadata() const
+    {
+        return metadata;
+    }
+
+    NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT(person_with_private_data_2, age, name, metadata)
+};
+
 class person_without_private_data_1
 {
  public:
@ -103,6 +139,41 @@ class person_without_private_data_2

 NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(person_without_private_data_2, age, name, metadata)

+class person_without_private_data_3
+{
+  public:
+    std::string name{};
+    int age = 0;
+    json metadata = nullptr;
+
+    bool operator==(const person_without_private_data_3& rhs) const
+    {
+        return name == rhs.name && age == rhs.age && metadata == rhs.metadata;
+    }
+
+    person_without_private_data_3() = default;
+    person_without_private_data_3(std::string name_, int age_, json metadata_)
+        : name(std::move(name_))
+        , age(age_)
+        , metadata(std::move(metadata_))
+    {}
+
+    std::string getName() const
+    {
+        return name;
+    }
+    int getAge() const
+    {
+        return age;
+    }
+    json getMetadata() const
+    {
+        return metadata;
+    }
+};
+
+NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT(person_without_private_data_3, age, name, metadata)
+
 class person_with_private_alphabet
 {
  public:
@ -231,7 +302,7 @@ NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(person_with_public_alphabet, a, b, c, d, e, f

 } // namespace persons

-TEST_CASE_TEMPLATE("Serialization/deserialization via NLOHMANN_DEFINE_TYPE_INTRUSIVE", T,
+TEST_CASE_TEMPLATE("Serialization/deserialization via NLOHMANN_DEFINE_TYPE_INTRUSIVE and NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE", T,
                   persons::person_with_private_data,
                   persons::person_without_private_data_1,
                   persons::person_without_private_data_2)
@ -257,6 +328,40 @@ TEST_CASE_TEMPLATE("Serialization/deserialization via NLOHMANN_DEFINE_TYPE_INTRU
    }
 }

+TEST_CASE_TEMPLATE("Serialization/deserialization via NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT and NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT", T,
+                   persons::person_with_private_data_2,
+                   persons::person_without_private_data_3)
+{
+    SECTION("person with default values")
+    {
+        // serialization of default constructed object
+        T p0;
+        CHECK(json(p0).dump() == "{\"age\":0,\"metadata\":null,\"name\":\"\"}");
+
+        // serialization
+        T p1("Erik", 1, {{"haircuts", 2}});
+        CHECK(json(p1).dump() == "{\"age\":1,\"metadata\":{\"haircuts\":2},\"name\":\"Erik\"}");
+
+        // deserialization
+        auto p2 = json(p1).get<T>();
+        CHECK(p2 == p1);
+
+        // roundtrip
+        CHECK(T(json(p1)) == p1);
+        CHECK(json(T(json(p1))) == json(p1));
+
+        // check default value in case of missing field
+        json j = json(p1);
+        j.erase("name");
+        j.erase("age");
+        j.erase("metadata");
+        T p3 = j.get<T>();
+        CHECK(p3.getName() == "");
+        CHECK(p3.getAge() == 0);
+        CHECK(p3.getMetadata() == nullptr);
+    }
+}
+
 TEST_CASE_TEMPLATE("Serialization/deserialization of classes with 26 public/private member variables via NLOHMANN_DEFINE_TYPE_INTRUSIVE and NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE", T,
                   persons::person_with_private_alphabet,
                   persons::person_with_public_alphabet)