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

@@ -416,6 +416,95 @@ template <typename Char> struct formatter<std::error_code, Char> {
   }
 };
 
+#if FMT_USE_RTTI
+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;
+  std::unique_ptr<char, void (*)(void*)> demangled_name_ptr(
+      abi::__cxa_demangle(ti.name(), nullptr, &size, &status), &std::free);
+
+  string_view demangled_name_view;
+  if (demangled_name_ptr) {
+    demangled_name_view = demangled_name_ptr.get();
+
+    // Normalization of stdlib inline namespace names.
+    // libc++ inline namespaces.
+    //  std::__1::*       -> std::*
+    //  std::__1::__fs::* -> std::*
+    // libstdc++ inline namespaces.
+    //  std::__cxx11::*             -> std::*
+    //  std::filesystem::__cxx11::* -> std::filesystem::*
+    if (demangled_name_view.starts_with("std::")) {
+      char* begin = demangled_name_ptr.get();
+      char* to = begin + 5;  // std::
+      for (char *from = to, *end = begin + demangled_name_view.size();
+           from < end;) {
+        // This is safe, because demangled_name is NUL-terminated.
+        if (from[0] == '_' && from[1] == '_') {
+          char* next = from + 1;
+          while (next < end && *next != ':') next++;
+          if (next[0] == ':' && next[1] == ':') {
+            from = next + 2;
+            continue;
+          }
+        }
+        *to++ = *from++;
+      }
+      demangled_name_view = {begin, detail::to_unsigned(to - begin)};
+    }
+  } else {
+    demangled_name_view = string_view(ti.name());
+  }
+  return detail::write_bytes<Char>(out, demangled_name_view);
+#  elif FMT_MSC_VERSION
+  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
+  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<
@@ -445,61 +534,11 @@ struct formatter<
       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;
-    std::unique_ptr<char, void (*)(void*)> demangled_name_ptr(
-        abi::__cxa_demangle(ti.name(), nullptr, &size, &status), &std::free);
-
-    string_view demangled_name_view;
-    if (demangled_name_ptr) {
-      demangled_name_view = demangled_name_ptr.get();
-
-      // Normalization of stdlib inline namespace names.
-      // libc++ inline namespaces.
-      //  std::__1::*       -> std::*
-      //  std::__1::__fs::* -> std::*
-      // libstdc++ inline namespaces.
-      //  std::__cxx11::*             -> std::*
-      //  std::filesystem::__cxx11::* -> std::filesystem::*
-      if (demangled_name_view.starts_with("std::")) {
-        char* begin = demangled_name_ptr.get();
-        char* to = begin + 5;  // std::
-        for (char *from = to, *end = begin + demangled_name_view.size();
-             from < end;) {
-          // This is safe, because demangled_name is NUL-terminated.
-          if (from[0] == '_' && from[1] == '_') {
-            char* next = from + 1;
-            while (next < end && *next != ':') next++;
-            if (next[0] == ':' && next[1] == ':') {
-              from = next + 2;
-              continue;
-            }
-          }
-          *to++ = *from++;
-        }
-        demangled_name_view = {begin, detail::to_unsigned(to - begin)};
-      }
-    } else {
-      demangled_name_view = string_view(ti.name());
-    }
-    out = 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);
-#  else
-    out = detail::write_bytes<Char>(out, string_view(ti.name())
-  });
-#  endif
+    out = detail::write_demangled_name<Char>(out, typeid(ex));
+#endif
     *out++ = ':';
     *out++ = ' ';
     return detail::write_bytes<Char>(out, string_view(ex.what()));
-#endif
   }
 };