Added std::type_info formatter

* 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

@@ -15,6 +15,7 @@
 #  include <cstdlib>
 #  include <exception>
 #  include <memory>
+#  include <string>
 #  include <thread>
 #  include <type_traits>
 #  include <typeinfo>
@@ -416,36 +417,33 @@ 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;
+#if FMT_USE_RTTI
+namespace details {
+template <typename Char>
+inline void remove_all_substrings(
+    std::basic_string<Char>& src,
+    std::type_identity_t<std::basic_string_view<Char>> pattern) {
+  const auto pattern_length = pattern.length();
+  for (auto i = src.find(pattern); i != std::basic_string<Char>::npos;
+       i = src.find(pattern))
+    src.erase(i, pattern_length);
+}
+}  // namespace details
 
+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()) {
-    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;
+    return ctx.begin();
   }
 
   template <typename Context>
-  auto format(const std::exception& ex, Context& ctx) const
-      -> decltype(ctx.out()) {
+  auto format(const std::type_info& ti,
+              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);
 #  ifdef FMT_HAS_ABI_CXA_DEMANGLE
     int status = 0;
     std::size_t size = 0;
@@ -484,21 +482,52 @@ 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);
+    std::basic_string<Char> demangled_name(ti.name());
+    details::remove_all_substrings(demangled_name, "class ");
+    details::remove_all_substrings(demangled_name, "enum ");
+    details::remove_all_substrings(demangled_name, "struct ");
+    return detail::write_bytes<Char>(out, demangled_name);
 #  else
-    out = detail::write_bytes<Char>(out, string_view(ti.name())
-  });
+    return detail::write_bytes<Char>(out, string_view(ti.name()));
 #  endif
-    *out++ = ':';
-    *out++ = ' ';
-    return detail::write_bytes<Char>(out, string_view(ex.what()));
+  }
+};
+#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 (!with_typename_)
+      return detail::write_bytes<Char>(out, string_view(ex.what()));
+
+#if FMT_USE_RTTI
+    const std::type_info& ti = typeid(ex);
+    auto format_imag = detail::string_literal<Char, '{', '}'>{};
+    return fmt::format_to(out, basic_string_view<Char>(format_imag), ti);
 #endif
   }
 };