Issue #45: Implement is_noexcept meta function

[delimbetov]

Issue number of the reported bug or feature request: #45

Describe your changes
Added is_noexcept as per P2996r3 spec.
The function checks for noexcept on:

1. (virtual) Method and it's type
2. Template method instantiation and it's type
3. Function and it's type
4. Function template instantiation and it's type
5. Lambda and it's type

For everything else it returns false.

Testing performed
Tests added to libcxx to cover all supported scenarios.

[katzdm]

Does this need to be a template? Seems like T will always be CXXMethodDecl.

[delimbetov]

It is CXXMethodDecl only in the "T->isRecordType()" branch. For "T->isFunctionPrototype()" it is FunctionProtoType.

I guess I could try extracting FunctionProtoType from CXXMethodDecl and make this function non-template. Would that be better if that's possible to do?

[katzdm]

Ahhh I see, sorry about that. How about we just take the ExceptionSpecificationType, and inline this as a lambda in the isFunctionOrLambdaNoexcept function?

static bool isFunctionOrLambdaNoexcept(const QualType QT) {
  static auto isExceptionSpecNoexcept = [](ExceptionSpecificationType) {
    switch (...) // ...
  }
  
  if (auto *FPT = dyn_cast<FunctionProtoType>(QT)) {
    return isExceptionSpecNoexcept(FPT->getExceptionSpecType());
  } else if (auto *RT = dyn_cast<RecordType>(QT)) {
    auto *RDecl = cast<CXXRecordDecl>(RT->getDecl());
    if (RDecl->isLambda() && !RDecl->isGenericLambda())
      return isExceptionSpecNoexcept(
          RDecl->getLambdaCallOperator()->getExceptionSpecType());
  }
  return false;
}

What do you think?

[delimbetov]

Sure, done