3rd-party/catch2
1
0
Fork 0
mirror of https://github.com/catchorg/Catch2.git synced 2025-08-01 21:05:39 +02:00
Code Issues Packages Projects Releases Wiki Activity

Move SFINAE in decomposer into return type

Browse Source 
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 commit is contained in:
Martin Hořeňovský
2022-12-08 16:31:55 +01:00
parent 2d7be1f7de
commit 28e651f152
3 changed files with 111 additions and 82 deletions
Download Patch File Download Diff File Expand all files Collapse all files

24
tests/SelfTest/UsageTests/Compilation.tests.cpp
View File

@@ -329,3 +329,27 @@ TEST_CASE( "#2555 - types that can only be compared with 0 literal (not int/long
REQUIRE( TypeWithLit0Comparisons{} != 0 );
REQUIRE_FALSE( 0 != TypeWithLit0Comparisons{} );
}
namespace {
struct MultipleImplicitConstructors {
MultipleImplicitConstructors( double ) {}
MultipleImplicitConstructors( int64_t ) {}
bool operator==( MultipleImplicitConstructors ) const { return true; }
bool operator!=( MultipleImplicitConstructors ) const { return true; }
bool operator<( MultipleImplicitConstructors ) const { return true; }
bool operator<=( MultipleImplicitConstructors ) const { return true; }
bool operator>( MultipleImplicitConstructors ) const { return true; }
bool operator>=( MultipleImplicitConstructors ) const { return true; }
};
}
TEST_CASE("#2571 - tests compile types that have multiple implicit constructors from lit 0",
"[compilation][approvals]") {
MultipleImplicitConstructors mic1( 0.0 );
MultipleImplicitConstructors mic2( 0.0 );
REQUIRE( mic1 == mic2 );
REQUIRE( mic1 != mic2 );
REQUIRE( mic1 < mic2 );
REQUIRE( mic1 <= mic2 );
REQUIRE( mic1 > mic2 );
REQUIRE( mic1 >= mic2 );
}