Extract function can extract code containing types defined in the enclosing functions scope

[5chmidti]

Clangd allows extracting a selection where a type is used that is defined in the scope of the enclosing function, making the type undefined in the extracted function.

void foo() {
      using MyType = int;
      [[MyType x = 42;
      MyType y = x;]]
}

void extracted() {
  MyType x = 42;
  MyType y = x;
}
void foo() {
  using MyType = int;
  extracted();
}

Clangd 17 at commit 852fe30b687e

I think this could be implemented by using a RecursiveASTVisitor to find all TypeDecls of the enclosing function and comparing those to the referenced Types within the selected region. If there exists a type that is declared in the enclosing function, but outside the selection, and that type is used within the selection, then don't extract.

[5chmidti]

The fix could address the FIXME comments in CapturedZoneInfo
https://github.com/llvm/llvm-project/blob/4c73549ebf171c1fa8039dc97e8fa260e824aa96/clang-tools-extra/clangd/refactor/tweaks/ExtractFunction.cpp#L529-L530

  // FIXME: capture TypeAliasDecl and UsingDirectiveDecl
  // FIXME: Capture type information as well.