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Improve compile-time formatting #4118

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d883061
Improve compile-time formatting
AnthonyVH Aug 7, 2024
ef611cb
Add NTTP format function
AnthonyVH Aug 19, 2024
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39 changes: 39 additions & 0 deletions include/fmt/compile.h
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Original file line number Diff line number Diff line change
Expand Up @@ -414,6 +414,21 @@ constexpr auto compile(S fmt) {
}
}
#endif // defined(__cpp_if_constexpr) && defined(__cpp_return_type_deduction)

#if FMT_USE_NONTYPE_TEMPLATE_ARGS
// A wrapper for non-type template arguments that automatically encapsulates
// string literals, but leaves other argument types as-is.
template <typename T> struct nttp_arg {
template <typename U = T> constexpr nttp_arg(U const& arg) : arg(arg) {}
T arg;
};

template <typename T> nttp_arg(const T&) -> nttp_arg<T>;

template <typename Char, size_t N>
nttp_arg(const Char (&arg)[N])
-> nttp_arg<fmt::detail_exported::fixed_string<Char, N>>;
#endif // FMT_USE_NONTYPE_TEMPLATE_ARGS
} // namespace detail

FMT_BEGIN_EXPORT
Expand Down Expand Up @@ -467,6 +482,8 @@ FMT_INLINE std::basic_string<typename S::char_type> format(const S&,
template <typename OutputIt, typename S, typename... Args,
FMT_ENABLE_IF(detail::is_compiled_string<S>::value)>
FMT_CONSTEXPR OutputIt format_to(OutputIt out, const S&, Args&&... args) {
// Check that all types are formattable.
[[maybe_unused]] auto formattable_check = fmt::make_format_args(args...);
constexpr auto compiled = detail::compile<Args...>(S());
if constexpr (std::is_same<remove_cvref_t<decltype(compiled)>,
detail::unknown_format>()) {
Expand Down Expand Up @@ -520,6 +537,28 @@ template <detail_exported::fixed_string Str> constexpr auto operator""_cf() {
Str>();
}
} // namespace literals

# if FMT_USE_CONSTEVAL
// Can't be consteval due to llvm bug preventing static constexpr members in
// a consteval function: https://github.com/llvm/llvm-project/issues/82994.
template <detail_exported::fixed_string format_str, detail::nttp_arg... args>
constexpr auto format()
-> basic_string_view<remove_cvref_t<decltype(format_str.data[0])>> {
using char_t = remove_cvref_t<decltype(format_str.data[0])>;
static constexpr auto str = [] consteval {
// clang-format off
using namespace literals;
constexpr auto compiled_format = operator""_cf<format_str>();
// clang-format on
constexpr auto result_length =
formatted_size(compiled_format, (args.arg)...);
auto result = detail_exported::fixed_string<char_t, result_length>{};
format_to(result.data, compiled_format, (args.arg)...);
return result;
}();
return basic_string_view(str.data, sizeof(str.data) / sizeof(char_t));
}
# endif // FMT_USE_CONSTEVAL
#endif

FMT_END_EXPORT
Expand Down
43 changes: 29 additions & 14 deletions include/fmt/format.h
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Expand Up @@ -964,13 +964,20 @@ class FMT_SO_VISIBILITY("default") format_error : public std::runtime_error {
namespace detail_exported {
#if FMT_USE_NONTYPE_TEMPLATE_ARGS
template <typename Char, size_t N> struct fixed_string {
constexpr fixed_string() = default;
constexpr fixed_string(const Char (&str)[N]) {
detail::copy<Char, const Char*, Char*>(static_cast<const Char*>(str),
str + N, data);
}
Char data[N] = {};
};
#endif

template <typename Char, size_t N>
constexpr auto format_as(fixed_string<Char, N> const& value)
-> basic_string_view<Char> {
return {value.data, N - 1};
}
#endif // FMT_USE_NONTYPE_TEMPLATE_ARGS

// Converts a compile-time string to basic_string_view.
template <typename Char, size_t N>
Expand Down Expand Up @@ -3624,11 +3631,13 @@ FMT_CONSTEXPR auto write(OutputIt out, const T& value) -> enable_if_t<

template <typename Char, typename OutputIt, typename T,
typename Context = basic_format_context<OutputIt, Char>>
FMT_CONSTEXPR auto write(OutputIt out, const T& value)
-> enable_if_t<mapped_type_constant<T, Context>::value ==
type::custom_type &&
!std::is_fundamental<T>::value,
OutputIt> {
FMT_CONSTEXPR auto write(OutputIt out, const T& value) -> enable_if_t<
mapped_type_constant<T, Context>::value == type::custom_type &&
!std::is_fundamental<T>::value &&
!std::is_same<
unformattable,
remove_cvref_t<decltype(arg_mapper<Context>().map(value))>>::value,
OutputIt> {
auto formatter = typename Context::template formatter_type<T>();
auto parse_ctx = typename Context::parse_context_type({});
formatter.parse(parse_ctx);
Expand Down Expand Up @@ -3879,19 +3888,21 @@ template <typename T, typename Char>
struct formatter<T, Char, enable_if_t<detail::has_format_as<T>::value>>
: formatter<detail::format_as_t<T>, Char> {
template <typename FormatContext>
auto format(const T& value, FormatContext& ctx) const -> decltype(ctx.out()) {
FMT_CONSTEXPR auto format(const T& value, FormatContext& ctx) const
-> decltype(ctx.out()) {
auto&& val = format_as(value); // Make an lvalue reference for format.
return formatter<detail::format_as_t<T>, Char>::format(val, ctx);
}
};

#define FMT_FORMAT_AS(Type, Base) \
template <typename Char> \
struct formatter<Type, Char> : formatter<Base, Char> { \
template <typename FormatContext> \
auto format(Type value, FormatContext& ctx) const -> decltype(ctx.out()) { \
return formatter<Base, Char>::format(value, ctx); \
} \
#define FMT_FORMAT_AS(Type, Base) \
template <typename Char> \
struct formatter<Type, Char> : formatter<Base, Char> { \
template <typename FormatContext> \
FMT_CONSTEXPR auto format(Type value, FormatContext& ctx) const \
-> decltype(ctx.out()) { \
return formatter<Base, Char>::format(value, ctx); \
} \
}

FMT_FORMAT_AS(signed char, int);
Expand Down Expand Up @@ -4235,6 +4246,10 @@ inline namespace literals {
* fmt::print("The answer is {answer}.", "answer"_a=42);
*/
# if FMT_USE_NONTYPE_TEMPLATE_ARGS
template <detail_exported::fixed_string Str> constexpr auto operator""_fs() {
return Str;
}

template <detail_exported::fixed_string Str> constexpr auto operator""_a() {
using char_t = remove_cvref_t<decltype(Str.data[0])>;
return detail::udl_arg<char_t, sizeof(Str.data) / sizeof(char_t), Str>();
Expand Down
150 changes: 95 additions & 55 deletions test/compile-test.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -288,90 +288,130 @@ TEST(compile_test, compile_format_string_literal) {
// (compiler file
// 'D:\a\_work\1\s\src\vctools\Compiler\CxxFE\sl\p1\c\constexpr\constexpr.cpp',
// line 8635)
#if FMT_USE_CONSTEVAL && \
(!FMT_MSC_VERSION || \
(FMT_MSC_VERSION >= 1928 && FMT_MSC_VERSION < 1930)) && \
// Can't support MSVC 19.28 & 19.29, because C++20 constexpr is required for
// fmt::v11::detail::buffer<T>::append.
#if FMT_USE_CONSTEVAL && (!FMT_MSC_VERSION || (FMT_MSC_VERSION >= 1939)) && \
defined(__cpp_lib_is_constant_evaluated)
template <size_t max_string_length, typename Char = char> struct test_string {
template <size_t max_string_length, typename Char = char>
struct fixed_length_string {
template <typename T> constexpr bool operator==(const T& rhs) const noexcept {
return fmt::basic_string_view<Char>(rhs).compare(buffer) == 0;
}
Char buffer[max_string_length]{};
};

template <size_t max_string_length, typename Char = char, typename... Args>
consteval auto test_format(auto format, const Args&... args) {
test_string<max_string_length, Char> string{};
consteval auto fixed_length_format(auto format, const Args&... args) {
fixed_length_string<max_string_length, Char> string{};
fmt::detail::ignore_unused(fmt::formatted_size(format, args...));
fmt::format_to(string.buffer, format, args...);
return string;
}

TEST(compile_time_formatting_test, bool) {
EXPECT_EQ("true", test_format<5>(FMT_COMPILE("{}"), true));
EXPECT_EQ("false", test_format<6>(FMT_COMPILE("{}"), false));
EXPECT_EQ("true ", test_format<6>(FMT_COMPILE("{:5}"), true));
EXPECT_EQ("1", test_format<2>(FMT_COMPILE("{:d}"), true));
}

TEST(compile_time_formatting_test, integer) {
EXPECT_EQ("42", test_format<3>(FMT_COMPILE("{}"), 42));
EXPECT_EQ("420", test_format<4>(FMT_COMPILE("{}"), 420));
EXPECT_EQ("42 42", test_format<6>(FMT_COMPILE("{} {}"), 42, 42));
EXPECT_EQ("42 42",
test_format<6>(FMT_COMPILE("{} {}"), uint32_t{42}, uint64_t{42}));

EXPECT_EQ("+42", test_format<4>(FMT_COMPILE("{:+}"), 42));
EXPECT_EQ("42", test_format<3>(FMT_COMPILE("{:-}"), 42));
EXPECT_EQ(" 42", test_format<4>(FMT_COMPILE("{: }"), 42));

EXPECT_EQ("-0042", test_format<6>(FMT_COMPILE("{:05}"), -42));
template <class UseNTTPFormat>
struct compile_time_formatting_test : testing::Test {
static constexpr bool use_nttp_format = UseNTTPFormat::value;
};

EXPECT_EQ("101010", test_format<7>(FMT_COMPILE("{:b}"), 42));
EXPECT_EQ("0b101010", test_format<9>(FMT_COMPILE("{:#b}"), 42));
EXPECT_EQ("0B101010", test_format<9>(FMT_COMPILE("{:#B}"), 42));
EXPECT_EQ("042", test_format<4>(FMT_COMPILE("{:#o}"), 042));
EXPECT_EQ("0x4a", test_format<5>(FMT_COMPILE("{:#x}"), 0x4a));
EXPECT_EQ("0X4A", test_format<5>(FMT_COMPILE("{:#X}"), 0x4a));
struct compile_time_formatting_test_name {
template <typename T> static std::string GetName(int) {
if constexpr (std::is_same_v<T, std::true_type>) {
return "nttp_format";
} else if constexpr (std::is_same_v<T, std::false_type>) {
return "fixed_length_format";
}
}
};

EXPECT_EQ(" 42", test_format<6>(FMT_COMPILE("{:5}"), 42));
EXPECT_EQ(" 42", test_format<6>(FMT_COMPILE("{:5}"), 42ll));
EXPECT_EQ(" 42", test_format<6>(FMT_COMPILE("{:5}"), 42ull));
// clang-format off
using compile_type_format_test_param_types = ::testing::Types<std::false_type
# if FMT_USE_NONTYPE_TEMPLATE_ARGS
, std::true_type
# endif // FMT_USE_NONTYPE_TEMPLATE_ARGS
>;
// clang-format on

TYPED_TEST_SUITE(compile_time_formatting_test,
compile_type_format_test_param_types,
compile_time_formatting_test_name);

# define GEN_FMT_COMPILE_RESULT(length, format_str, ...) \
[] { \
if constexpr (TestFixture::use_nttp_format) { \
return fmt::format<format_str __VA_OPT__(, ) __VA_ARGS__>(); \
} else { \
return fixed_length_format<length>(FMT_COMPILE(format_str) \
__VA_OPT__(, ) __VA_ARGS__); \
} \
}()

TYPED_TEST(compile_time_formatting_test, bool) {
EXPECT_EQ("true", (GEN_FMT_COMPILE_RESULT(5, "{}", true)));
EXPECT_EQ("false", (GEN_FMT_COMPILE_RESULT(6, "{}", false)));
EXPECT_EQ("true ", (GEN_FMT_COMPILE_RESULT(6, "{:5}", true)));
EXPECT_EQ("1", (GEN_FMT_COMPILE_RESULT(2, "{:d}", true)));
}

EXPECT_EQ("42 ", test_format<5>(FMT_COMPILE("{:<4}"), 42));
EXPECT_EQ(" 42", test_format<5>(FMT_COMPILE("{:>4}"), 42));
EXPECT_EQ(" 42 ", test_format<5>(FMT_COMPILE("{:^4}"), 42));
EXPECT_EQ("**-42", test_format<6>(FMT_COMPILE("{:*>5}"), -42));
TYPED_TEST(compile_time_formatting_test, integer) {
EXPECT_EQ("42", (GEN_FMT_COMPILE_RESULT(3, "{}", 42)));
EXPECT_EQ("420", (GEN_FMT_COMPILE_RESULT(4, "{}", 420)));
EXPECT_EQ("42 42", (GEN_FMT_COMPILE_RESULT(6, "{} {}", 42, 42)));
EXPECT_EQ("42 42",
(GEN_FMT_COMPILE_RESULT(6, "{} {}", uint32_t{42}, uint64_t{42})));

EXPECT_EQ("+42", (GEN_FMT_COMPILE_RESULT(4, "{:+}", 42)));
EXPECT_EQ("42", (GEN_FMT_COMPILE_RESULT(3, "{:-}", 42)));
EXPECT_EQ(" 42", (GEN_FMT_COMPILE_RESULT(4, "{: }", 42)));

EXPECT_EQ("-0042", (GEN_FMT_COMPILE_RESULT(6, "{:05}", -42)));

EXPECT_EQ("101010", (GEN_FMT_COMPILE_RESULT(7, "{:b}", 42)));
EXPECT_EQ("0b101010", (GEN_FMT_COMPILE_RESULT(9, "{:#b}", 42)));
EXPECT_EQ("0B101010", (GEN_FMT_COMPILE_RESULT(9, "{:#B}", 42)));
EXPECT_EQ("042", (GEN_FMT_COMPILE_RESULT(4, "{:#o}", 042)));
EXPECT_EQ("0x4a", (GEN_FMT_COMPILE_RESULT(5, "{:#x}", 0x4a)));
EXPECT_EQ("0X4A", (GEN_FMT_COMPILE_RESULT(5, "{:#X}", 0x4a)));

EXPECT_EQ(" 42", (GEN_FMT_COMPILE_RESULT(6, "{:5}", 42)));
EXPECT_EQ(" 42", (GEN_FMT_COMPILE_RESULT(6, "{:5}", 42l)));
EXPECT_EQ(" 42", (GEN_FMT_COMPILE_RESULT(6, "{:5}", 42ll)));
EXPECT_EQ(" 42", (GEN_FMT_COMPILE_RESULT(6, "{:5}", 42ull)));

EXPECT_EQ("42 ", (GEN_FMT_COMPILE_RESULT(5, "{:<4}", 42)));
EXPECT_EQ(" 42", (GEN_FMT_COMPILE_RESULT(5, "{:>4}", 42)));
EXPECT_EQ(" 42 ", (GEN_FMT_COMPILE_RESULT(5, "{:^4}", 42)));
EXPECT_EQ("**-42", (GEN_FMT_COMPILE_RESULT(6, "{:*>5}", -42)));
}

TEST(compile_time_formatting_test, char) {
EXPECT_EQ("c", test_format<2>(FMT_COMPILE("{}"), 'c'));
TYPED_TEST(compile_time_formatting_test, char) {
EXPECT_EQ("c", (GEN_FMT_COMPILE_RESULT(2, "{}", 'c')));

EXPECT_EQ("c ", test_format<4>(FMT_COMPILE("{:3}"), 'c'));
EXPECT_EQ("99", test_format<3>(FMT_COMPILE("{:d}"), 'c'));
EXPECT_EQ("c ", (GEN_FMT_COMPILE_RESULT(4, "{:3}", 'c')));
EXPECT_EQ("99", (GEN_FMT_COMPILE_RESULT(3, "{:d}", 'c')));
}

TEST(compile_time_formatting_test, string) {
EXPECT_EQ("42", test_format<3>(FMT_COMPILE("{}"), "42"));
TYPED_TEST(compile_time_formatting_test, string) {
EXPECT_EQ("42", (GEN_FMT_COMPILE_RESULT(3, "{}", "42")));
EXPECT_EQ("The answer is 42",
test_format<17>(FMT_COMPILE("{} is {}"), "The answer", "42"));
(GEN_FMT_COMPILE_RESULT(17, "{} is {}", "The answer", "42")));

EXPECT_EQ("abc**", test_format<6>(FMT_COMPILE("{:*<5}"), "abc"));
EXPECT_EQ("**🤡**", test_format<9>(FMT_COMPILE("{:*^6}"), "🤡"));
EXPECT_EQ("abc**", (GEN_FMT_COMPILE_RESULT(6, "{:*<5}", "abc")));
EXPECT_EQ("**🤡**", (GEN_FMT_COMPILE_RESULT(9, "{:*^6}", "🤡")));
}

TEST(compile_time_formatting_test, combination) {
TYPED_TEST(compile_time_formatting_test, combination) {
EXPECT_EQ("420, true, answer",
test_format<18>(FMT_COMPILE("{}, {}, {}"), 420, true, "answer"));
(GEN_FMT_COMPILE_RESULT(18, "{}, {}, {}", 420, true, "answer")));

EXPECT_EQ(" -42", test_format<5>(FMT_COMPILE("{:{}}"), -42, 4));
EXPECT_EQ(" -42", (GEN_FMT_COMPILE_RESULT(5, "{:{}}", -42, 4)));
}

TEST(compile_time_formatting_test, custom_type) {
EXPECT_EQ("foo", test_format<4>(FMT_COMPILE("{}"), test_formattable()));
EXPECT_EQ("bar", test_format<4>(FMT_COMPILE("{:b}"), test_formattable()));
TYPED_TEST(compile_time_formatting_test, custom_type) {
EXPECT_EQ("foo", (GEN_FMT_COMPILE_RESULT(4, "{}", test_formattable{})));
EXPECT_EQ("bar", (GEN_FMT_COMPILE_RESULT(4, "{:b}", test_formattable{})));
}

TEST(compile_time_formatting_test, multibyte_fill) {
EXPECT_EQ("жж42", test_format<8>(FMT_COMPILE("{:ж>4}"), 42));
TYPED_TEST(compile_time_formatting_test, multibyte_fill) {
EXPECT_EQ("жж42", (GEN_FMT_COMPILE_RESULT(8, "{:ж>4}", 42)));
}
#endif