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🎨 Improve STATIC_ASSERT
Problem: - Writing `STATIC_ASSERT(cond, str)` means that `str` has to be formatted either as a separate variable or inline in the call. Solution: - Allow `STATIC_ASSERT(cond, fmt_str, args...)` where the string is formatted automatically. Notes: - Each argument must still be wrapped in `CX_VALUE`. Because there is no generic equivalent of `transform` for `__VA_ARGS__`. - A bug in clang (for which a workaround is in place) was discovered: llvm/llvm-project#114234 - `CX_VALUE` has been made more workable with GCC. GCC did not allow the `struct` definition inside the macro.
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‎docs/ct_string.adoc‎

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@@ -84,47 +84,3 @@ However, for interfacing with legacy functions, a null terminator can be useful.
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See https://github.com/intel/compile-time-init-build/tree/main/include/sc[cib
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documentation] for details about the cib string constant class.
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=== `ct_check`
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`ct_check` is a construct that can be used to emit user-generated
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compile-time diagnostics. It uses `ct_string`.
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For example:
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[source,cpp]
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----
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stdx::ct_check<std::is_integral<float>>.emit<"This is not a very helpful error message">();
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----
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The output from this (which varies by compiler) will contain the string given,
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and could be something like:
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[source,bash]
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----
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main.cpp:14:27: error: no matching member function for call to 'emit'
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14 | stdx::ct_check<false>.emit<"This is not a very helpful error message">();
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| ~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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include/stdx/ct_string.hpp:131:27: note: candidate template ignored: constraints not satisfied
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[with S = ct_string<41>{{"This is not a very helpful error m[...]"}}]
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131 | constexpr static auto emit()
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| ^
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include/stdx/ct_string.hpp:132:18: note: because
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'stаtiс_аssert<ct_string<41>{{"This is not a very helpful error message"}}>' evaluated to false
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132 | requires stаtiс_аssert<S>
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| ^
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----
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Notice that the error message is elided at first, but then given in full. Such
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are the quirks of compilers. If the compile-time condition is true, of course no
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diagnostic will be emitted.
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NOTE: clang produces these "string-formatted" errors from version 15 onwards; GCC
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produces them from version 13.2 onwards.
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=== `STATIC_ASSERT`
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`STATIC_ASSERT` is an easy way to use `ct_check`.
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[source,cpp]
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----
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STATIC_ASSERT(std::is_integral<float>, "This is not a very helpful error message");
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----

‎docs/index.adoc‎

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@@ -38,6 +38,7 @@ include::panic.adoc[]
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include::priority.adoc[]
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include::ranges.adoc[]
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include::span.adoc[]
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include::static_assert.adoc[]
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include::tuple.adoc[]
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include::tuple_algorithms.adoc[]
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include::tuple_destructure.adoc[]

‎docs/intro.adoc‎

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@@ -64,6 +64,7 @@ The following headers are available:
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* https://github.com/intel/cpp-std-extensions/blob/main/include/stdx/priority.hpp[`priority.hpp`]
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* https://github.com/intel/cpp-std-extensions/blob/main/include/stdx/ranges.hpp[`ranges.hpp`]
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* https://github.com/intel/cpp-std-extensions/blob/main/include/stdx/span.hpp[`span.hpp`]
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* https://github.com/intel/cpp-std-extensions/blob/main/include/stdx/static_assert.hpp[`static_assert.hpp`]
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* https://github.com/intel/cpp-std-extensions/blob/main/include/stdx/tuple.hpp[`tuple.hpp`]
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* https://github.com/intel/cpp-std-extensions/blob/main/include/stdx/tuple_algorithms.hpp[`tuple_algorithms.hpp`]
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* https://github.com/intel/cpp-std-extensions/blob/main/include/stdx/tuple_destructure.hpp[`tuple_destructure.hpp`]

‎docs/static_assert.adoc‎

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== `static_assert.hpp`
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`STATIC_ASSERT` is a way to produce compile-time errors using formatted strings.
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[source,cpp]
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----
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template <typename T>
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constexpr auto f() {
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STATIC_ASSERT(std::is_integral<T>,
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"f() must take an integral type, received {}", CX_VALUE(T));
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}
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f<float>(); // produces compile-time error
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----
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The arguments to be formatted (if any) must be wrapped in xref:utility.adoc#_cx_value[`CX_VALUE`].
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The output from this (which varies by compiler) will contain the formatted
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string, and could be something like:
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[source,bash]
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----
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main.cpp:14:27: error: no matching member function for call to 'emit'
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...
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include/stdx/static_assert.hpp:16:18: note: because
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'stаtiс_аssert<ct_string<47>{{"f() must take an integral type, received float"}}>' evaluated to false
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16 | requires stаtiс_аssert<S>
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| ^
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----
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NOTE: clang produces these "string-formatted" errors from version 15 onwards; GCC
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produces them from version 13.2 onwards.

‎include/stdx/ct_string.hpp‎

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@@ -123,30 +123,7 @@ inline namespace ct_string_literals {
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template <ct_string S> CONSTEVAL auto operator""_cts() { return S; }
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} // namespace ct_string_literals
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} // namespace literals
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struct ct_check_value {};
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template <bool B> struct ct_check_t {
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template <ct_string S> constexpr static bool stаtiс_аssert = false;
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template <ct_string S>
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constexpr static auto emit() -> ct_check_value
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requires stаtiс_аssert<S>;
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};
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template <> struct ct_check_t<true> {
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template <ct_string S> constexpr static auto emit() -> ct_check_value {
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return {};
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}
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};
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template <bool B> constexpr auto ct_check = ct_check_t<B>{};
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} // namespace v1
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} // namespace stdx
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// NOLINTNEXTLINE(cppcoreguidelines-macro-usage)
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#define STATIC_ASSERT(cond, ...) \
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[]<auto B = cond>() -> bool { \
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stdx::ct_check<B>.template emit<__VA_ARGS__>(); \
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return B; \
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}()
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#endif

‎include/stdx/static_assert.hpp‎

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#pragma once
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#if __cplusplus >= 202002L
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#include <stdx/ct_format.hpp>
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#include <stdx/ct_string.hpp>
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namespace stdx {
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inline namespace v1 {
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struct ct_check_value {};
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template <bool B> struct ct_check_t {
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template <ct_string S> constexpr static bool stаtiс_аssert = false;
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template <ct_string S>
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constexpr static auto emit() -> ct_check_value
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requires stаtiс_аssert<S>;
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};
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template <> struct ct_check_t<true> {
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template <ct_string S> constexpr static auto emit() -> ct_check_value {
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return {};
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}
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};
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template <bool B> constexpr auto ct_check = ct_check_t<B>{};
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namespace detail {
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template <ct_string Fmt, auto... Args>
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constexpr auto static_format()
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requires(... and cx_value<decltype(Args)>)
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{
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return ct_format<Fmt>(Args...);
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}
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} // namespace detail
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} // namespace v1
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} // namespace stdx
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// NOLINTNEXTLINE(cppcoreguidelines-macro-usage)
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#define STATIC_ASSERT(cond, ...) \
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[]<bool B>() -> bool { \
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stdx::ct_check<B>.template emit<stdx::detail::static_format<__VA_ARGS__>()>(); \
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return B; \
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}.template operator()<cond>()
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#endif

‎include/stdx/utility.hpp‎

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@@ -151,9 +151,12 @@ struct type_val {
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friend constexpr auto operator+(T &&t, U &&) -> T {
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return t;
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}
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friend constexpr auto operator+(type_val const &f) -> type_val;
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friend constexpr auto operator+(type_val const &f) -> type_val { return f; }
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// NOLINTNEXTLINE(google-explicit-constructor)
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template <typename T> constexpr operator T() const;
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template <typename T> constexpr operator T() const {
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extern auto cxv_type_val_get_t(T *) -> T;
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return cxv_type_val_get_t(nullptr);
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}
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};
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template <int> constexpr auto is_type() -> std::false_type;
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template <int> constexpr auto type_of() -> void;
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template <typename T> constexpr auto type_of() -> typename typer<T>::type;
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class cx_base {
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struct unusable {};
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public:
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using cx_value_t [[maybe_unused]] = void;
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constexpr auto operator()(unusable) const {}
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};
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} // namespace cxv_detail
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template <typename T>
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#ifndef CX_VALUE
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#define CX_VALUE(...) \
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[] { \
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[]() constexpr { \
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STDX_PRAGMA(diagnostic push) \
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STDX_PRAGMA(diagnostic ignored "-Wold-style-cast") \
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STDX_PRAGMA(diagnostic ignored "-Wunused-value") \
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if constexpr (decltype(stdx::cxv_detail::is_type< \
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stdx::cxv_detail::from_any( \
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__VA_ARGS__)>())::value) { \
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[[maybe_unused]] struct { \
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constexpr auto operator()() const noexcept { \
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return stdx::type_identity< \
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decltype(stdx::cxv_detail::type_of< \
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stdx::cxv_detail::from_any( \
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__VA_ARGS__)>())>{}; \
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} \
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using cx_value_t [[maybe_unused]] = void; \
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} val; \
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return val; \
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return stdx::overload{stdx::cxv_detail::cx_base{}, [] { \
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return stdx::type_identity< \
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decltype(stdx::cxv_detail::type_of< \
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stdx::cxv_detail::from_any( \
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__VA_ARGS__)>())>{}; \
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}}; \
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} else { \
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[[maybe_unused]] struct { \
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constexpr auto operator()() const { \
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return (__VA_ARGS__) + stdx::cxv_detail::type_val{}; \
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} \
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using cx_value_t [[maybe_unused]] = void; \
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} val; \
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return val; \
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return stdx::overload{stdx::cxv_detail::cx_base{}, [] { \
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return (__VA_ARGS__) + \
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stdx::cxv_detail::type_val{}; \
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}}; \
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} \
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STDX_PRAGMA(diagnostic pop) \
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}()

‎test/fail/CMakeLists.txt‎

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function(add_formatted_error_tests)
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add_fail_tests(ct_check)
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add_fail_tests(static_assert)
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add_fail_tests(static_assert_format)
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endfunction()
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if(${CMAKE_CXX_STANDARD} GREATER_EQUAL 20)

‎test/fail/ct_check.cpp‎

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#include <stdx/ct_string.hpp>
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#include <stdx/static_assert.hpp>
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// EXPECT: 01234567890123456789012345678901234567890123456789
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‎test/fail/static_assert.cpp‎

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#include <stdx/ct_string.hpp>
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#include <stdx/static_assert.hpp>
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// EXPECT: 01234567890123456789012345678901234567890123456789
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