Added std::type_info formatter (#3978)

* Added std::type_info formatter;
* Reused std::type_info formatter in std::exception formatters;
* Updated MSVC std::type_info outputting to exclude all class, struct and enum occurences.

include/fmt/std.h

@@ -416,36 +416,11 @@ template <typename Char> struct formatter<std::error_code, Char> {
   }
 };
 
-FMT_EXPORT
-template <typename T, typename Char>
-struct formatter<
-    T, Char,  // DEPRECATED! Mixing code unit types.
-    typename std::enable_if<std::is_base_of<std::exception, T>::value>::type> {
- private:
-  bool with_typename_ = false;
-
- public:
-  FMT_CONSTEXPR auto parse(basic_format_parse_context<Char>& ctx)
-      -> decltype(ctx.begin()) {
-    auto it = ctx.begin();
-    auto end = ctx.end();
-    if (it == end || *it == '}') return it;
-    if (*it == 't') {
-      ++it;
-      with_typename_ = FMT_USE_RTTI != 0;
-    }
-    return it;
-  }
-
-  template <typename Context>
-  auto format(const std::exception& ex, Context& ctx) const
-      -> decltype(ctx.out()) {
-    auto out = ctx.out();
-    if (!with_typename_)
-      return detail::write_bytes<Char>(out, string_view(ex.what()));
-
 #if FMT_USE_RTTI
-    const std::type_info& ti = typeid(ex);
+namespace detail {
+
+template <typename Char, typename OutputIt>
+auto write_demangled_name(OutputIt out, const std::type_info& ti) -> OutputIt {
 #  ifdef FMT_HAS_ABI_CXA_DEMANGLE
   int status = 0;
   std::size_t size = 0;
@@ -484,22 +459,85 @@ struct formatter<
   } else {
     demangled_name_view = string_view(ti.name());
   }
-    out = detail::write_bytes<Char>(out, demangled_name_view);
+  return detail::write_bytes<Char>(out, demangled_name_view);
 #  elif FMT_MSC_VERSION
-    string_view demangled_name_view(ti.name());
-    if (demangled_name_view.starts_with("class "))
-      demangled_name_view.remove_prefix(6);
-    else if (demangled_name_view.starts_with("struct "))
-      demangled_name_view.remove_prefix(7);
-    out = detail::write_bytes<Char>(out, demangled_name_view);
+  const string_view demangled_name(ti.name());
+  for (std::size_t i = 0; i < demangled_name.size(); ++i) {
+    auto sub = demangled_name;
+    sub.remove_prefix(i);
+    if (sub.starts_with("enum ")) {
+      i += 4;
+      continue;
+    }
+    if (sub.starts_with("class ") || sub.starts_with("union ")) {
+      i += 5;
+      continue;
+    }
+    if (sub.starts_with("struct ")) {
+      i += 6;
+      continue;
+    }
+    if (*sub.begin() != ' ') *out++ = *sub.begin();
+  }
+  return out;
 #  else
-    out = detail::write_bytes<Char>(out, string_view(ti.name())
-  });
+  return detail::write_bytes<Char>(out, string_view(ti.name()));
 #  endif
+}
+
+}  // namespace detail
+
+FMT_EXPORT
+template <typename Char>
+struct formatter<std::type_info, Char  // DEPRECATED! Mixing code unit types.
+                 > {
+ public:
+  FMT_CONSTEXPR auto parse(basic_format_parse_context<Char>& ctx)
+      -> decltype(ctx.begin()) {
+    return ctx.begin();
+  }
+
+  template <typename Context>
+  auto format(const std::type_info& ti, Context& ctx) const
+      -> decltype(ctx.out()) {
+    return detail::write_demangled_name<Char>(ctx.out(), ti);
+  }
+};
+#endif
+
+FMT_EXPORT
+template <typename T, typename Char>
+struct formatter<
+    T, Char,  // DEPRECATED! Mixing code unit types.
+    typename std::enable_if<std::is_base_of<std::exception, T>::value>::type> {
+ private:
+  bool with_typename_ = false;
+
+ public:
+  FMT_CONSTEXPR auto parse(basic_format_parse_context<Char>& ctx)
+      -> decltype(ctx.begin()) {
+    auto it = ctx.begin();
+    auto end = ctx.end();
+    if (it == end || *it == '}') return it;
+    if (*it == 't') {
+      ++it;
+      with_typename_ = FMT_USE_RTTI != 0;
+    }
+    return it;
+  }
+
+  template <typename Context>
+  auto format(const std::exception& ex, Context& ctx) const
+      -> decltype(ctx.out()) {
+    auto out = ctx.out();
+#if FMT_USE_RTTI
+    if (with_typename_) {
+      out = detail::write_demangled_name<Char>(out, typeid(ex));
       *out++ = ':';
       *out++ = ' ';
-    return detail::write_bytes<Char>(out, string_view(ex.what()));
+    }
 #endif
+    return detail::write_bytes<Char>(out, string_view(ex.what()));
   }
 };
 

test/std-test.cc

@@ -300,6 +300,13 @@ TEST(std_test, exception) {
 #endif
 }
 
+#if FMT_USE_RTTI
+TEST(std_test, type_info) {
+  EXPECT_EQ(fmt::format("{}", typeid(std::runtime_error)),
+            "std::runtime_error");
+}
+#endif
+
 TEST(std_test, format_bit_reference) {
   std::bitset<2> bs(1);
   EXPECT_EQ(fmt::format("{} {}", bs[0], bs[1]), "true false");