add test for compile-time formatting

test/CMakeLists.txt

@@ -146,6 +146,15 @@ else ()
   target_compile_definitions(header-only-test PRIVATE FMT_HEADER_ONLY=1)
 endif ()
 
+if (${CMAKE_CXX_STANDARD} GREATER_EQUAL "20")
+  add_fmt_executable(compile-time-formatting-test
+      compile-time-formatting-test.cc test-main.cc)
+  target_link_libraries(compile-time-formatting-test gmock)
+  target_include_directories(compile-time-formatting-test SYSTEM PUBLIC gtest gmock)
+  target_link_libraries(compile-time-formatting-test fmt::fmt-header-only)
+  add_test(NAME compile-time-formatting-test COMMAND compile-time-formatting-test)
+endif ()
+
 message(STATUS "FMT_PEDANTIC: ${FMT_PEDANTIC}")
 
 if (FMT_PEDANTIC)

test/compile-time-formatting-test.cc

@@ -0,0 +1,66 @@
+#include <array>
+#include <string>
+
+#include "fmt/compile.h"
+#include "fmt/core.h"
+#include "gmock.h"
+#include "gtest-extra.h"
+
+template <size_t max_string_length> struct constexpr_buffer_helper {
+  template <typename Func>
+  constexpr constexpr_buffer_helper& modify(Func func) {
+    func(buffer);
+    return *this;
+  }
+
+  template <typename T> constexpr bool operator==(const T& rhs) const noexcept {
+    return (std::string_view(rhs).compare(buffer.data()) == 0);
+  }
+
+  std::array<char, max_string_length> buffer{};
+};
+
+TEST(CompileTimeFormattingTest, OneInteger) {
+  constexpr auto result42 =
+      constexpr_buffer_helper<3>{}.modify([](auto& buffer) {
+        fmt::format_to(buffer.data(), FMT_COMPILE("{}"), 42);
+      });
+  EXPECT_EQ(result42, "42");
+  constexpr auto result420 =
+      constexpr_buffer_helper<3>{}.modify([](auto& buffer) {
+        fmt::format_to(buffer.data(), FMT_COMPILE("{}"), 420);
+      });
+  EXPECT_EQ(result420, "420");
+}
+
+TEST(CompileTimeFormattingTest, TwoIntegers) {
+  constexpr auto result = constexpr_buffer_helper<6>{}.modify([](auto& buffer) {
+    fmt::format_to(buffer.data(), FMT_COMPILE("{} {}"), 41, 43);
+  });
+  EXPECT_EQ(result, "41 43");
+}
+
+TEST(CompileTimeFormattingTest, OneString) {
+  constexpr auto result = constexpr_buffer_helper<3>{}.modify([](auto& buffer) {
+    fmt::format_to(buffer.data(), FMT_COMPILE("{}"), "42");
+  });
+  EXPECT_EQ(result, "42");
+}
+
+TEST(CompileTimeFormattingTest, TwoStrings) {
+  constexpr auto result =
+      constexpr_buffer_helper<17>{}.modify([](auto& buffer) {
+        fmt::format_to(buffer.data(), FMT_COMPILE("{} is {}"), "The answer",
+                       "42");
+      });
+  EXPECT_EQ(result, "The answer is 42");
+}
+
+TEST(CompileTimeFormattingTest, StringAndInteger) {
+  constexpr auto result =
+      constexpr_buffer_helper<17>{}.modify([](auto& buffer) {
+        fmt::format_to(buffer.data(), FMT_COMPILE("{} is {}"), "The answer",
+                       42);
+      });
+  EXPECT_EQ(result, "The answer is 42");
+}