From 8f45f23be0c97624e72a5713458a0dfe704fb46b Mon Sep 17 00:00:00 2001
From: Daniela Engert <dani@ngrt.de>
Date: Fri, 4 Jun 2021 17:29:22 +0200
Subject: [PATCH] Support compile-time format string compilation (module)

---
 include/fmt/compile.h | 20 ++++++++++----------
 test/module-test.cc   |  8 ++++++++
 2 files changed, 18 insertions(+), 10 deletions(-)

diff --git a/include/fmt/compile.h b/include/fmt/compile.h
index 003be9e78414b..0be0b7720cf55 100644
--- a/include/fmt/compile.h
+++ b/include/fmt/compile.h
@@ -11,7 +11,12 @@
 #include "format.h"
 
 FMT_BEGIN_NAMESPACE
-namespace detail {
+FMT_MODULE_EXPORT_BEGIN
+
+// A compile-time string which is compiled into fast formatting code.
+class compiled_string {};
+
+FMT_BEGIN_DETAIL_NAMESPACE
 
 // An output iterator that counts the number of objects written to it and
 // discards them.
@@ -137,11 +142,8 @@ class truncating_iterator<OutputIt, std::true_type>
   truncating_iterator& operator*() { return *this; }
 };
 
-// A compile-time string which is compiled into fast formatting code.
-class compiled_string {};
-
 template <typename S>
-struct is_compiled_string : std::is_base_of<compiled_string, S> {};
+struct is_compiled_string : std::is_base_of<fmt::compiled_string, S> {};
 
 /**
   \rst
@@ -157,15 +159,14 @@ struct is_compiled_string : std::is_base_of<compiled_string, S> {};
   \endrst
  */
 #ifdef __cpp_if_constexpr
-#  define FMT_COMPILE(s) \
-    FMT_STRING_IMPL(s, fmt::detail::compiled_string, explicit)
+#  define FMT_COMPILE(s) FMT_STRING_IMPL(s, fmt::compiled_string, explicit)
 #else
 #  define FMT_COMPILE(s) FMT_STRING(s)
 #endif
 
 #if FMT_USE_NONTYPE_TEMPLATE_PARAMETERS
 template <typename Char, size_t N, fmt::ct::str<Char, N> Str>
-struct udl_compiled_string : compiled_string {
+struct udl_compiled_string : fmt::compiled_string {
   using char_type = Char;
   constexpr operator basic_string_view<char_type>() const {
     return {Str.data, N - 1};
@@ -527,9 +528,8 @@ constexpr auto compile(S format_str) {
   }
 }
 #endif  // __cpp_if_constexpr
-}  // namespace detail
 
-FMT_MODULE_EXPORT_BEGIN
+FMT_END_DETAIL_NAMESPACE
 
 #ifdef __cpp_if_constexpr
 
diff --git a/test/module-test.cc b/test/module-test.cc
index fee0e12eeae49..69b6099a7b97f 100644
--- a/test/module-test.cc
+++ b/test/module-test.cc
@@ -555,3 +555,11 @@ TEST(module_test, has_formatter) {
 TEST(module_test, is_formattable) {
   EXPECT_FALSE(fmt::is_formattable<disabled_formatter>::value);
 }
+
+TEST(module_test, compile_format_string) {
+  using namespace fmt::literals;
+  EXPECT_EQ("42", fmt::format("{0:x}"_cf, 0x42));
+  EXPECT_EQ(L"42", fmt::format(L"{:}"_cf, 42));
+  EXPECT_EQ("4.2", fmt::format("{arg:3.1f}"_cf, "arg"_a = 4.2));
+  EXPECT_EQ(L" 42", fmt::format(L"{arg:>3}"_cf, L"arg"_a = L"42"));
+}