Add class name output to formatter for std::exception

Signed-off-by: Vladislav Shchapov <vladislav@shchapov.ru>

include/fmt/core.h

@@ -486,6 +486,18 @@ template <typename Char> class basic_string_view {
     size_ -= n;
   }
 
+  FMT_CONSTEXPR_CHAR_TRAITS bool starts_with(
+      basic_string_view<Char> sv) const noexcept {
+    return size_ >= sv.size_ &&
+           std::char_traits<Char>::compare(data_, sv.data_, sv.size_) == 0;
+  }
+  FMT_CONSTEXPR_CHAR_TRAITS bool starts_with(Char c) const noexcept {
+    return size_ >= 1 && std::char_traits<Char>::eq(*data_, c);
+  }
+  FMT_CONSTEXPR_CHAR_TRAITS bool starts_with(const Char* s) const {
+    return starts_with(basic_string_view<Char>(s));
+  }
+
   // Lexicographically compare this string reference to other.
   FMT_CONSTEXPR_CHAR_TRAITS auto compare(basic_string_view other) const -> int {
     size_t str_size = size_ < other.size_ ? size_ : other.size_;

include/fmt/std.h

@@ -8,9 +8,12 @@
 #ifndef FMT_STD_H_
 #define FMT_STD_H_
 
+#include <cstdlib>
 #include <exception>
+#include <memory>
 #include <thread>
 #include <type_traits>
+#include <typeinfo>
 #include <utility>
 
 #include "ostream.h"
@@ -28,6 +31,16 @@
 #  endif
 #endif
 
+#if FMT_HAS_INCLUDE(<cxxabi.h>)
+#  include <cxxabi.h>
+#  ifndef __GABIXX_CXXABI_H__
+#    define FMT_HAS_CXXABI_H 1
+#  endif
+#endif
+#ifndef FMT_HAS_CXXABI_H
+#  define FMT_HAS_CXXABI_H 0
+#endif
+
 #ifdef __cpp_lib_filesystem
 FMT_BEGIN_NAMESPACE
 
@@ -178,7 +191,33 @@ struct formatter<
   template <typename FormatContext>
   auto format(const std::exception& ex, FormatContext& ctx) const ->
       typename FormatContext::iterator {
-    return fmt::formatter<string_view>::format(ex.what(), ctx);
+    basic_memory_buffer<Char> msg;
+    const std::type_info& ti = typeid(ex);
+#if FMT_HAS_CXXABI_H
+    int status = 0;
+    std::size_t size = 0;
+    std::unique_ptr<char, decltype(std::free)*> demangled_name(
+        abi::__cxa_demangle(ti.name(), nullptr, &size, &status), std::free);
+    if (demangled_name) {
+      msg.append(string_view(demangled_name.get()));
+    } else {
+      msg.append(string_view(ti.name()));
+    }
+#elif FMT_MSC_VERSION
+    string_view sv(ti.name());
+    if (sv.starts_with("class "))
+      sv.remove_prefix(6);
+    else if (sv.starts_with("struct "))
+      sv.remove_prefix(7);
+    msg.append(sv);
+#else
+    msg.append(string_view(ti.name()));
+#endif
+    msg.append(string_view(": "));
+    msg.append(string_view(ex.what()));
+
+    return fmt::formatter<string_view>::format(
+        basic_string_view<Char>(msg.data(), msg.size()), ctx);
   }
 };
 FMT_END_NAMESPACE

test/std-test.cc

@@ -11,7 +11,9 @@
 #include <vector>
 
 #include "fmt/ranges.h"
-#include "gtest/gtest.h"
+#include "gtest-extra.h"
+
+using testing::Contains;
 
 TEST(std_test, path) {
 #ifdef __cpp_lib_filesystem
@@ -78,21 +80,22 @@ TEST(std_test, variant) {
 #endif
 }
 
-TEST(std_test, exception) {
-  std::string str("Test Exception");
-  std::string escstr = fmt::format("\"{}\"", str);
-
+template <typename Catch> void exception_test() {
   try {
-    throw std::runtime_error(str);
-  } catch (const std::exception& ex) {
-    EXPECT_EQ(fmt::format("{}", ex), str);
-    EXPECT_EQ(fmt::format("{:?}", ex), escstr);
+    throw std::runtime_error("Test Exception");
+  } catch (const Catch& ex) {
+    // St13runtime_error - libstdc++ with old ABI.
+    EXPECT_THAT((std::vector<std::string>{"std::runtime_error: Test Exception",
+                                          "St13runtime_error: Test Exception"}),
+                Contains(fmt::format("{}", ex)));
+    EXPECT_THAT(
+        (std::vector<std::string>{"\"std::runtime_error: Test Exception\"",
+                                  "\"St13runtime_error: Test Exception\""}),
+        Contains(fmt::format("{:?}", ex)));
   }
+}
 
-  try {
-    throw std::runtime_error(str);
-  } catch (const std::runtime_error& ex) {
-    EXPECT_EQ(fmt::format("{}", ex), str);
-    EXPECT_EQ(fmt::format("{:?}", ex), escstr);
-  }
+TEST(std_test, exception) {
+  exception_test<std::exception>();
+  exception_test<std::runtime_error>();
 }