From 355be4b13fe340964a1419bd4d4c7e89db5a3174 Mon Sep 17 00:00:00 2001
From: Victor Zverovich <victor.zverovich@gmail.com>
Date: Wed, 28 Apr 2021 09:11:47 -0700
Subject: [PATCH] Make FMT_COMPILE fallback on runtime without if constexpr
 (#2261)

---
 include/fmt/compile.h | 6 +++++-
 test/compile-test.cc  | 6 ++++++
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/include/fmt/compile.h b/include/fmt/compile.h
index d231c83e..4d541c87 100644
--- a/include/fmt/compile.h
+++ b/include/fmt/compile.h
@@ -114,7 +114,11 @@ struct is_compiled_string : std::is_base_of<compiled_string, S> {};
     std::string s = fmt::format(FMT_COMPILE("{}"), 42);
   \endrst
  */
-#define FMT_COMPILE(s) FMT_STRING_IMPL(s, fmt::detail::compiled_string)
+#ifdef __cpp_if_constexpr
+#  define FMT_COMPILE(s) FMT_STRING_IMPL(s, fmt::detail::compiled_string)
+#else
+#  define FMT_COMPILE(s) FMT_STRING(s)
+#endif
 
 #if FMT_USE_NONTYPE_TEMPLATE_PARAMETERS
 template <typename Char, size_t N, fixed_string<Char, N> Str>
diff --git a/test/compile-test.cc b/test/compile-test.cc
index 56056ec4..31db499a 100644
--- a/test/compile-test.cc
+++ b/test/compile-test.cc
@@ -155,6 +155,12 @@ TEST(CompileTest, EmptyFormatString) {
   EXPECT_EQ(fmt::format(f), "");
 }
 
+TEST(CompileTest, CompileFallback) {
+  // FMT_COMPILE should fallback on runtime formatting when `if constexpr` is
+  // not available.
+  EXPECT_EQ("42", fmt::format(FMT_COMPILE("{}"), 42));
+}
+
 #ifdef __cpp_if_constexpr
 TEST(CompileTest, FormatDefault) {
   EXPECT_EQ("42", fmt::format(FMT_COMPILE("{}"), 42));