From 397ad1bec34febe61b72f57134681a64150beba8 Mon Sep 17 00:00:00 2001
From: Victor Zverovich <viz@fb.com>
Date: Mon, 15 Jun 2020 18:13:40 -0700
Subject: [PATCH] Optimize common case

---
 include/fmt/format-inl.h | 19 +++++++++++++++++++
 include/fmt/format.h     |  3 +--
 test/format-test.cc      |  2 +-
 3 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/include/fmt/format-inl.h b/include/fmt/format-inl.h
index d0080907..ea4821c2 100644
--- a/include/fmt/format-inl.h
+++ b/include/fmt/format-inl.h
@@ -1365,7 +1365,26 @@ FMT_FUNC void report_system_error(int error_code,
   report_error(format_system_error, error_code, message);
 }
 
+struct stringifier {
+  template <typename T> FMT_INLINE std::string operator()(T value) const {
+    return to_string(value);
+  }
+  std::string operator()(basic_format_arg<format_context>::handle h) const {
+    memory_buffer buf;
+    internal::buffer<char>& base = buf;
+    format_parse_context parse_ctx({});
+    format_context format_ctx(std::back_inserter(base), {}, {});
+    h.format(parse_ctx, format_ctx);
+    return to_string(buf);
+  }
+};
+
 FMT_FUNC std::string detail::vformat(string_view format_str, format_args args) {
+  if (format_str.size() == 2 && equal2(format_str.data(), "{}")) {
+    auto arg = args.get(0);
+    if (!arg) error_handler().on_error("argument not found");
+    return visit_format_arg(stringifier(), arg);
+  }
   memory_buffer buffer;
   detail::vformat_to(buffer, format_str, args);
   return to_string(buffer);
diff --git a/include/fmt/format.h b/include/fmt/format.h
index 7dab11b5..2f13c8ec 100644
--- a/include/fmt/format.h
+++ b/include/fmt/format.h
@@ -1766,8 +1766,7 @@ template <typename OutputIt, typename Char> struct default_arg_formatter {
   }
 
   OutputIt operator()(typename basic_format_arg<context>::handle handle) {
-    auto s = Char('}');
-    basic_format_parse_context<Char> parse_ctx(basic_string_view<Char>(&s, 1));
+    basic_format_parse_context<Char> parse_ctx({});
     basic_format_context<OutputIt, Char> format_ctx(out, args, loc);
     handle.format(parse_ctx, format_ctx);
     return format_ctx.out();
diff --git a/test/format-test.cc b/test/format-test.cc
index 5edd9460..22fd12be 100644
--- a/test/format-test.cc
+++ b/test/format-test.cc
@@ -1475,7 +1475,7 @@ template <> struct formatter<Date> {
   template <typename ParseContext>
   FMT_CONSTEXPR auto parse(ParseContext& ctx) -> decltype(ctx.begin()) {
     auto it = ctx.begin();
-    if (*it == 'd') ++it;
+    if (it != ctx.end() && *it == 'd') ++it;
     return it;
   }