From 1daae555b342157fd9e2cda37fef371e8b233212 Mon Sep 17 00:00:00 2001
From: Victor Zverovich <viz@fb.com>
Date: Wed, 14 Jun 2023 21:46:15 +0300
Subject: [PATCH] Optimize format string compilation

---
 include/fmt/compile.h | 7 ++++++-
 include/fmt/core.h    | 7 +++++++
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/include/fmt/compile.h b/include/fmt/compile.h
index 46cbc8fc319f..57f3a961445b 100644
--- a/include/fmt/compile.h
+++ b/include/fmt/compile.h
@@ -221,7 +221,12 @@ template <typename Char, typename T, int N> struct field {
 
   template <typename OutputIt, typename... Args>
   constexpr OutputIt format(OutputIt out, const Args&... args) const {
-    return write<Char>(out, get_arg_checked<T, N>(args...));
+    const T& arg = get_arg_checked<T, N>(args...);
+    if constexpr (std::is_convertible_v<T, basic_string_view<Char>>) {
+      auto s = basic_string_view<Char>(arg);
+      return copy_str<Char>(s.begin(), s.end(), out);
+    }
+    return write<Char>(out, arg);
   }
 };
 
diff --git a/include/fmt/core.h b/include/fmt/core.h
index 4961310a311f..966033fe02b0 100644
--- a/include/fmt/core.h
+++ b/include/fmt/core.h
@@ -1486,6 +1486,13 @@ auto copy_str(InputIt begin, InputIt end, appender out) -> appender {
   get_container(out).append(begin, end);
   return out;
 }
+template <typename Char, typename InputIt>
+auto copy_str(InputIt begin, InputIt end,
+              std::back_insert_iterator<std::string> out)
+    -> std::back_insert_iterator<std::string> {
+  get_container(out).append(begin, end);
+  return out;
+}
 
 template <typename Char, typename R, typename OutputIt>
 FMT_CONSTEXPR auto copy_str(R&& rng, OutputIt out) -> OutputIt {