From 6e33d881e2c86d542250ad1a5fe5e43a98a2317e Mon Sep 17 00:00:00 2001
From: Vladislav Shchapov <vladislav@shchapov.ru>
Date: Wed, 28 Sep 2022 00:07:32 +0500
Subject: [PATCH] Normalization of stdlib inline namespace names

Signed-off-by: Vladislav Shchapov <vladislav@shchapov.ru>
---
 include/fmt/std.h | 32 ++++++++++++++++++++++++++++----
 test/std-test.cc  | 19 ++++++++++++++++++-
 2 files changed, 46 insertions(+), 5 deletions(-)

diff --git a/include/fmt/std.h b/include/fmt/std.h
index 02ca6721..7f484274 100644
--- a/include/fmt/std.h
+++ b/include/fmt/std.h
@@ -214,10 +214,34 @@ struct formatter<
     std::size_t size = 0;
     std::unique_ptr<char, decltype(&std::free)> demangled_name_ptr(
         abi::__cxa_demangle(ti.name(), nullptr, &size, &status), &std::free);
-    out = detail::write_bytes(
-        out,
-        string_view(demangled_name_ptr ? demangled_name_ptr.get() : ti.name()),
-        spec);
+    string_view demangled_name_view(
+        demangled_name_ptr ? demangled_name_ptr.get() : ti.name());
+
+    // Normalization of stdlib inline namespace names.
+    if (demangled_name_view.starts_with("std::")) {
+      // Separation of user's and system exception classes.
+      demangled_name_view.remove_prefix(5);
+      out = detail::write_bytes(out, string_view("std::"), spec);
+
+      // libc++ inline namespaces.
+      // std::__1::*       -> std::*
+      // std::__1::__fs::* -> std::*
+      if (demangled_name_view.starts_with("__1::")) {
+        demangled_name_view.remove_prefix(5);
+        if (demangled_name_view.starts_with("__fs::"))
+          demangled_name_view.remove_prefix(6);
+      }
+      // libstdc++ inline namespaces.
+      // std::__cxx11::*             -> std::*
+      // std::filesystem::__cxx11::* -> std::filesystem::*
+      else if (demangled_name_view.starts_with("__cxx11::")) {
+        demangled_name_view.remove_prefix(9);
+      } else if (demangled_name_view.starts_with("filesystem::__cxx11::")) {
+        demangled_name_view.remove_prefix(21);
+        out = detail::write_bytes(out, string_view("filesystem::"), spec);
+      }
+    }
+    out = detail::write_bytes(out, demangled_name_view, spec);
 #elif FMT_MSC_VERSION
     string_view demangled_name_view(ti.name());
     if (demangled_name_view.starts_with("class "))
diff --git a/test/std-test.cc b/test/std-test.cc
index 0f6bf11a..f700a510 100644
--- a/test/std-test.cc
+++ b/test/std-test.cc
@@ -11,7 +11,9 @@
 #include <vector>
 
 #include "fmt/ranges.h"
-#include "gtest/gtest.h"
+#include "gtest-extra.h"  // StartsWith
+
+using testing::StartsWith;
 
 TEST(std_test, path) {
 #ifdef __cpp_lib_filesystem
@@ -116,4 +118,19 @@ TEST(std_test, exception) {
               fmt::format("{:t}", ex));
     EXPECT_EQ("My Exception", fmt::format("{:}", ex));
   }
+
+  try {
+    throw std::system_error(std::error_code(), "message");
+  } catch (const std::system_error& ex) {
+    EXPECT_THAT(fmt::format("{:t}", ex), StartsWith("std::system_error: "));
+  }
+
+#ifdef __cpp_lib_filesystem
+  try {
+    throw std::filesystem::filesystem_error("message", std::error_code());
+  } catch (const std::filesystem::filesystem_error& ex) {
+    EXPECT_THAT(fmt::format("{:t}", ex),
+                StartsWith("std::filesystem::filesystem_error: "));
+  }
+#endif
 }