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Document issue with spaceship operator in assertion and MSVC

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Martin Hořeňovský 2024-02-16 21:54:25 +01:00
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@ -173,3 +173,19 @@ TEST_CASE("b") {
If you are seeing a problem like this, i.e. weird test paths that trigger only under Clang with `libc++`, or only under very specific version of `libstdc++`, it is very likely you are seeing this. The only known workaround is to use a fixed version of your standard library.
### Visual Studio 2022 -- can't compile assertion with the spaceship operator
[The C++ standard requires that `std::foo_ordering` is only comparable with
a literal 0](https://eel.is/c++draft/cmp#categories.pre-3). There are
multiple strategies a stdlib implementation can take to achieve this, and
MSVC's STL has changed the strategy they use between two releases of VS 2022.
With the new strategy, `REQUIRE((a <=> b) == 0)` no longer compiles under
MSVC. Note that Catch2 can compile code using MSVC STL's new strategy,
but only when compiled with a C++20 conforming compiler. MSVC is currently
not conformant enough, but `clang-cl` will compile the assertion above
using MSVC STL without problem.
This change got in with MSVC v19.37](https://godbolt.org/z/KG9obzdvE).