From b5c02fceea3ca84632dba267e9700b689c0feeb9 Mon Sep 17 00:00:00 2001
From: Zach Toogood <zrtoogood@gmail.com>
Date: Sat, 27 Aug 2022 20:59:47 +0300
Subject: [PATCH] Add formatter for std::exception

Co-authored-by: fekir <federico.kircheis@gmail.com>
Co-authored-by: Alexey Ochapov <alexez@alexez.com>
---
 include/fmt/std.h | 18 +++++++++++++++++-
 test/std-test.cc  | 31 ++++++++++++++++++++++++++++++-
 2 files changed, 47 insertions(+), 2 deletions(-)

diff --git a/include/fmt/std.h b/include/fmt/std.h
index 41d2b2838b6d7..39fa776244d06 100644
--- a/include/fmt/std.h
+++ b/include/fmt/std.h
@@ -8,6 +8,7 @@
 #ifndef FMT_STD_H_
 #define FMT_STD_H_
 
+#include <exception>
 #include <thread>
 #include <type_traits>
 #include <utility>
@@ -166,6 +167,21 @@ struct formatter<
   }
 };
 FMT_END_NAMESPACE
-#endif
+
+#endif  // __cpp_lib_variant
+
+FMT_BEGIN_NAMESPACE
+template <typename T, typename Char>
+struct formatter<
+    T, Char,
+    typename std::enable_if<std::is_base_of<std::exception, T>::value>::type>
+    : formatter<string_view> {
+  template <typename FormatContext>
+  auto format(const std::exception& ex, FormatContext& ctx) const ->
+      typename FormatContext::iterator {
+    return fmt::formatter<string_view>::format(ex.what(), ctx);
+  }
+};
+FMT_END_NAMESPACE
 
 #endif  // FMT_STD_H_
diff --git a/test/std-test.cc b/test/std-test.cc
index c22b3e38fb39b..d3008d6fd6f69 100644
--- a/test/std-test.cc
+++ b/test/std-test.cc
@@ -6,11 +6,11 @@
 // For the license information refer to format.h.
 
 #include "fmt/std.h"
-#include "fmt/ranges.h"
 
 #include <string>
 #include <vector>
 
+#include "fmt/ranges.h"
 #include "gtest/gtest.h"
 
 TEST(std_test, path) {
@@ -77,3 +77,32 @@ TEST(std_test, variant) {
   EXPECT_EQ(fmt::format("{}", v5), "variant(\"yes, this is variant\")");
 #endif
 }
+
+TEST(std_test, exception) {
+#if (defined(__GNUC__) && __GNUC__ <= 8 ) || (defined(__clang__) && __clang__ <= 8) || defined(_APPLE__)
+    std::string str("vector");
+#elif defined(__clang__) || defined(__GNUC__)
+  std::string str("vector::_M_range_check: __n (which is 42) >= this->size() (which is 0)");
+#elif defined(_MSC_VER) && _MSC_VER > 1920
+  std::string str("invalid vector subscript");
+#else
+   std::string str("invalid vector<T> subscript");
+#endif
+  std::string escstr = fmt::format("\"{}\"", str);
+
+  try {
+    std::vector<int> vec;
+    std::ignore = vec.at(42);
+  } catch (const std::exception& ex) {
+    EXPECT_EQ(fmt::format("{}", ex), str);
+    EXPECT_EQ(fmt::format("{:?}", ex), escstr);
+  }
+
+  try {
+    std::vector<int> vec;
+    std::ignore = vec.at(42);
+  } catch (const std::out_of_range& ex) {
+    EXPECT_EQ(fmt::format("{}", ex), str);
+    EXPECT_EQ(fmt::format("{:?}", ex), escstr);
+  }
+}