From d3c680409041e76e3e2f9ff370698943e7d93e90 Mon Sep 17 00:00:00 2001
From: Vladislav Shchapov <vladislav@shchapov.ru>
Date: Fri, 2 Sep 2022 21:09:52 +0500
Subject: [PATCH] Add class name output to formatter for std::exception

Signed-off-by: Vladislav Shchapov <vladislav@shchapov.ru>
---
 include/fmt/std.h | 41 ++++++++++++++++++++++++++++++++++++++++-
 test/std-test.cc  | 42 ++++++++++++++++++++++++++++++------------
 2 files changed, 70 insertions(+), 13 deletions(-)

diff --git a/include/fmt/std.h b/include/fmt/std.h
index 63dbebe3179d0..442691c0faba4 100644
--- a/include/fmt/std.h
+++ b/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>) || defined(__GLIBCXX__)
+#  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
 
@@ -175,7 +188,33 @@ 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
diff --git a/test/std-test.cc b/test/std-test.cc
index 77cf793454c3c..243b6820bb7fa 100644
--- a/test/std-test.cc
+++ b/test/std-test.cc
@@ -81,21 +81,39 @@ 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) {
+    EXPECT_EQ("std::runtime_error: Test Exception", fmt::format("{}", ex));
+    EXPECT_EQ("\"std::runtime_error: Test Exception\"",
+              fmt::format("{:?}", ex));
   }
+}
+
+namespace my_ns1 {
+namespace my_ns2 {
+struct my_exception : public std::exception {
+ private:
+  std::string msg;
+
+ public:
+  my_exception(const std::string& s) : msg(s) {}
+  const char* what() const noexcept override;
+};
+const char* my_exception::what() const noexcept { return msg.c_str(); }
+}  // namespace my_ns2
+}  // namespace my_ns1
+
+TEST(std_test, exception) {
+  exception_test<std::exception>();
+  exception_test<std::runtime_error>();
 
   try {
-    throw std::runtime_error(str);
-  } catch (const std::runtime_error& ex) {
-    EXPECT_EQ(fmt::format("{}", ex), str);
-    EXPECT_EQ(fmt::format("{:?}", ex), escstr);
+    using namespace my_ns1::my_ns2;
+    throw my_exception("My Exception");
+  } catch (const std::exception& ex) {
+    EXPECT_EQ("my_ns1::my_ns2::my_exception: My Exception",
+              fmt::format("{}", ex));
   }
 }