Martin Hořeňovský
28e651f152
This is needed so that we can use conjunction and other logical type traits to workaround issue with older GCC versions (8 and below), when they run into types that have ambiguous constructor from `0`, see e.g. #2571. However, using conjunction and friends in the SFINAE constraint in the template parameter breaks for C++20 and up, due to the new comparison operator rewriting rules. With C++20, when the compiler see `a == b`, it also tries `b == a` and collects overload set for both of these expressions. In Catch2, this means that e.g. `REQUIRE( 1 == 2 )` would lead the compiler to check overloads for both `ExprLhs<int> == int` and `int == ExprLhs<int>`. Since the overload set and SFINAE constraints assume that `ExprLhs<T>` is always on the left side, when the compiler tries to resolve the template parameters, all hell breaks loose and the compilation fails. By moving the SFINAE constraints to the return type, the compiler can discard the switched expression without having to resolve the complex SFINAE constraints, and thus everything works the way it is supposed to. Fixes #2571
76 lines
3.0 KiB
C++
76 lines
3.0 KiB
C++
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// Copyright Catch2 Authors
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// Distributed under the Boost Software License, Version 1.0.
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// (See accompanying file LICENSE.txt or copy at
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// https://www.boost.org/LICENSE_1_0.txt)
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// SPDX-License-Identifier: BSL-1.0
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#ifndef CATCH_COMPARE_TRAITS_HPP_INCLUDED
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#define CATCH_COMPARE_TRAITS_HPP_INCLUDED
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#include <catch2/internal/catch_void_type.hpp>
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#include <type_traits>
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namespace Catch {
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namespace Detail {
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#if defined( __GNUC__ ) && !defined( __clang__ )
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# pragma GCC diagnostic push
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// GCC likes to complain about comparing bool with 0, in the decltype()
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// that defines the comparable traits below.
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# pragma GCC diagnostic ignored "-Wbool-compare"
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// "ordered comparison of pointer with integer zero" same as above,
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// but it does not have a separate warning flag to suppress
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# pragma GCC diagnostic ignored "-Wextra"
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// Did you know that comparing floats with `0` directly
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// is super-duper dangerous in unevaluated context?
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# pragma GCC diagnostic ignored "-Wfloat-equal"
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#endif
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#if defined( __clang__ )
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# pragma clang diagnostic push
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// Did you know that comparing floats with `0` directly
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// is super-duper dangerous in unevaluated context?
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# pragma clang diagnostic ignored "-Wfloat-equal"
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#endif
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#define CATCH_DEFINE_COMPARABLE_TRAIT( id, op ) \
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template <typename, typename, typename = void> \
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struct is_##id##_comparable : std::false_type {}; \
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template <typename T, typename U> \
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struct is_##id##_comparable< \
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T, \
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U, \
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void_t<decltype( std::declval<T>() op std::declval<U>() )>> \
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: std::true_type {}; \
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template <typename, typename = void> \
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struct is_##id##_0_comparable : std::false_type {}; \
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template <typename T> \
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struct is_##id##_0_comparable<T, \
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void_t<decltype( std::declval<T>() op 0 )>> \
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: std::true_type {};
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// We need all 6 pre-spaceship comparison ops: <, <=, >, >=, ==, !=
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CATCH_DEFINE_COMPARABLE_TRAIT( lt, < )
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CATCH_DEFINE_COMPARABLE_TRAIT( le, <= )
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CATCH_DEFINE_COMPARABLE_TRAIT( gt, > )
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CATCH_DEFINE_COMPARABLE_TRAIT( ge, >= )
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CATCH_DEFINE_COMPARABLE_TRAIT( eq, == )
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CATCH_DEFINE_COMPARABLE_TRAIT( ne, != )
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#undef CATCH_DEFINE_COMPARABLE_TRAIT
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#if defined( __GNUC__ ) && !defined( __clang__ )
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# pragma GCC diagnostic pop
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#endif
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#if defined( __clang__ )
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# pragma clang diagnostic pop
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#endif
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} // namespace Detail
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} // namespace Catch
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#endif // CATCH_COMPARE_TRAITS_HPP_INCLUDED
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