Bug 261598 – [MSVC][Win] Using C++20's concept cause WinCairo compiler to crash

• Component: Tools / Tests
• Status: RESOLVED DUPLICATE

[Jean-Yves Avenard [:jya]]

(Using Tools / Test component for lack of a better component)

I added usage of C++20 concept in a PR, WinCairo bots crashes when parsing that file.

https://ews-build.webkit.org/#/builders/32/builds/17174

This is the added code causing an issue:

```
class NativePromiseBase;

template <typename T>
concept IsNativePromise = std::is_base_of<NativePromiseBase, T>::value;

template <typename T, typename U>
concept RelatedNativePromise = requires(T, U)
{
    { IsNativePromise<T> };
    { IsNativePromise<U> };
    { std::is_same<typename T::NativePromiseBaseType, typename U::NativePromiseBaseType>::value };
};
```

[Jean-Yves Avenard [:jya]]

The compiler crashes with:

```
C:\BW\WinCairo-EWS\build\WebKitBuild\Release\WTF\Headers\wtf/TypeTraits.h(134): fatal error C1001: Internal compiler error.
```

[Jean-Yves Avenard [:jya]]

I can confirm that it's just this one:

```
template <typename T, typename U>
concept RelatedNativePromise = requires(T, U)
{
    { IsNativePromise<T> };
    { IsNativePromise<U> };
    { std::is_same<typename T::NativePromiseBaseType, typename U::NativePromiseBaseType>::value };
};
```

that causes the crash

[Jean-Yves Avenard [:jya]]

Wth the migration from mcvc to clang-cl this may no longer be an issue.

[Fujii Hironori]

The migration isn't completed yet. I will remove the #if after the migration is completed.

[Fujii Hironori]

WebKit Windows port hasn't dropped MSVC support yet.
VS 2022 v17.9.6 still reports the internal compiler error for wtf/TypeTraits.h.

[Fujii Hironori]

*** This bug has been marked as a duplicate of bug 274018 ***