💥 throw exception if nullptr is passed to parse function

Addresses #3584

docs/mkdocs/docs/api/basic_json/parse.md

@@ -28,7 +28,7 @@ static basic_json parse(IteratorType first, IteratorType last,
 :   A compatible input, for instance:
     
     - an `std::istream` object
-    - a `FILE` pointer
+    - a `FILE` pointer (will throw [json.exception.parse_error.116](../../home/exceptions.md#jsonexceptionparse_error116) if passed pointer is `#!cpp nullptr`)
     - a C-style array of characters
     - a pointer to a null-terminated string of single byte characters
     - a `std::string`

docs/mkdocs/docs/home/exceptions.md

@@ -354,6 +354,16 @@ A UBJSON high-precision number could not be parsed.
     [json.exception.parse_error.115] parse error at byte 5: syntax error while parsing UBJSON high-precision number: invalid number text: 1A
     ```
 
+### json.exception.parse_error.116
+
+A `#!cpp FILE*` pointer passed to the [parse](../api/basic_json/parse.md) function is `#!cpp nullptr`; that is, a previous call to `#!cpp std::fopen` failed.
+
+!!! failure "Example message"
+
+    ```
+    [json.exception.parse_error.116] parse error: input file is invalid: No such file or directory
+    ```
+
 ## Iterator errors
 
 This exception is thrown if iterators passed to a library function do not match

include/nlohmann/detail/input/input_adapters.hpp

@@ -9,8 +9,9 @@
 #pragma once
 
 #include <array> // array
+#include <cerrno> // errno
 #include <cstddef> // size_t
-#include <cstring> // strlen
+#include <cstring> // strlen, strerror
 #include <iterator> // begin, end, iterator_traits, random_access_iterator_tag, distance, next
 #include <memory> // shared_ptr, make_shared, addressof
 #include <numeric> // accumulate
@@ -48,9 +49,14 @@ class file_input_adapter
     using char_type = char;
 
     JSON_HEDLEY_NON_NULL(2)
-    explicit file_input_adapter(std::FILE* f) noexcept
+    explicit file_input_adapter(std::FILE* f)
         : m_file(f)
-    {}
+    {
+        if (m_file == nullptr)
+        {
+            JSON_THROW(parse_error::create(116, 0, detail::concat("input file is invalid: ", reinterpret_cast<const char*>(std::strerror(errno))), nullptr));
+        }
+    }
 
     // make class move-only
     file_input_adapter(const file_input_adapter&) = delete;

single_include/nlohmann/json.hpp

@@ -5893,8 +5893,9 @@ std::size_t hash(const BasicJsonType& j)
 
 
 #include <array> // array
+#include <cerrno> // errno
 #include <cstddef> // size_t
-#include <cstring> // strlen
+#include <cstring> // strlen, strerror
 #include <iterator> // begin, end, iterator_traits, random_access_iterator_tag, distance, next
 #include <memory> // shared_ptr, make_shared, addressof
 #include <numeric> // accumulate
@@ -5934,9 +5935,14 @@ class file_input_adapter
     using char_type = char;
 
     JSON_HEDLEY_NON_NULL(2)
-    explicit file_input_adapter(std::FILE* f) noexcept
+    explicit file_input_adapter(std::FILE* f)
         : m_file(f)
-    {}
+    {
+        if (m_file == nullptr)
+        {
+            JSON_THROW(parse_error::create(116, 0, detail::concat("input file is invalid: ", reinterpret_cast<const char*>(std::strerror(errno))), nullptr));
+        }
+    }
 
     // make class move-only
     file_input_adapter(const file_input_adapter&) = delete;

tests/src/unit-deserialization.cpp

@@ -332,6 +332,12 @@ TEST_CASE("deserialization")
         {
             CHECK_THROWS_WITH_AS("[\"foo\",1,2,3,false,{\"one\":1}"_json, "[json.exception.parse_error.101] parse error at line 1, column 29: syntax error while parsing array - unexpected end of input; expected ']'", json::parse_error&);
         }
+
+        SECTION("FILE*")
+        {
+            std::FILE* f = std::fopen("nonexisting_file", "r"); // NOTLINT(cppcoreguidelines-owning-memory)
+            CHECK_THROWS_WITH_AS(json::parse(f), "[json.exception.parse_error.116] parse error: input file is invalid: No such file or directory", json::parse_error&);
+        }
     }
 
     SECTION("contiguous containers")