From 943532fecee35f3d0f8fda7fa8431a85b36c50ce Mon Sep 17 00:00:00 2001
From: Victor Zverovich <viz@fb.com>
Date: Wed, 20 May 2020 14:59:57 -0700
Subject: [PATCH] Make ostream formatter work with compile-time format strings
 (#1692)

---
 include/fmt/ostream.h | 3 ++-
 test/ostream-test.cc  | 4 ++++
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/include/fmt/ostream.h b/include/fmt/ostream.h
index 597316d8..72ba1da0 100644
--- a/include/fmt/ostream.h
+++ b/include/fmt/ostream.h
@@ -110,7 +110,8 @@ void format_value(buffer<Char>& buf, const T& value,
 template <typename T, typename Char>
 struct fallback_formatter<T, Char, enable_if_t<is_streamable<T, Char>::value>>
     : private formatter<basic_string_view<Char>, Char> {
-  auto parse(basic_format_parse_context<Char>& ctx) -> decltype(ctx.begin()) {
+  FMT_CONSTEXPR auto parse(basic_format_parse_context<Char>& ctx)
+      -> decltype(ctx.begin()) {
     return formatter<basic_string_view<Char>, Char>::parse(ctx);
   }
   template <typename ParseCtx,
diff --git a/test/ostream-test.cc b/test/ostream-test.cc
index a6cb07f5..b7be4796 100644
--- a/test/ostream-test.cc
+++ b/test/ostream-test.cc
@@ -302,3 +302,7 @@ std::ostream& operator<<(std::ostream& os, copyfmt_test) {
 TEST(OStreamTest, CopyFmt) {
   EXPECT_EQ("foo", fmt::format("{}", copyfmt_test()));
 }
+
+TEST(OStreamTest, CompileTimeString) {
+  EXPECT_EQ("42", fmt::format(FMT_STRING("{}"), 42));
+}