catch3/src/catch2/internal/catch_compare_traits.hpp, branch v3.2.1 Progmasoft Catch3: an independently maintained C++17 test framework with a parallel runner, property checks, snapshots and structured results. Move SFINAE in decomposer into return type 2022-12-08T23:40:01+00:00 Martin Hořeňovský 2022-12-08T15:31:55+00:00 28e651f1521449f2fce8b202307b6312a0ebe429 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 
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
Support decomposing types that only compare with literal 0 2022-11-04T18:24:44+00:00 Martin Hořeňovský 2022-11-01T14:01:43+00:00 ec59cd8736b7ee8fcd69c76c71c2a0b72293b00c This is primarily done to support new `std::*_ordering` types, but the refactoring also supports any other type with this property. The compilation overhead is surprisingly low. Testing it with clang on a Linux machine, compiling our SelfTest project takes only 2-3% longer with these changes than it takes otherwise. Closes #2555 
This is primarily done to support new `std::*_ordering` types,
but the refactoring also supports any other type with this
property.

The compilation overhead is surprisingly low. Testing it with
clang on a Linux machine, compiling our SelfTest project takes
only 2-3% longer with these changes than it takes otherwise.

Closes #2555
Add traits for checking whether types are comparable 2022-11-04T18:24:42+00:00 Martin Hořeňovský 2022-11-01T07:48:23+00:00 d7f8c36e4cb856ee632b4ca01f8d5847984aa276