[all-commits] [llvm/llvm-project] 485212: [Sema]Use tag name lookup for class names (#112166)

[Gábor Spaits via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 48521209aa4d95a97564f8a5af7ccca09c6ede5d
      https://github.com/llvm/llvm-project/commit/48521209aa4d95a97564f8a5af7ccca09c6ede5d
  Author: Gábor Spaits <gaborspaits1 at gmail.com>
  Date:   2024-10-15 (Tue, 15 Oct 2024)

  Changed paths:
    M clang/docs/ReleaseNotes.rst
    M clang/lib/Sema/SemaDecl.cpp
    M clang/test/CXX/class.derived/p2.cpp

  Log Message:
  -----------
  [Sema]Use tag name lookup for class names (#112166)

This PR would fix #16855 .

The correct lookup to use for class names is Tag name lookup,
because it does not take namespaces into account. The lookup before
does and because of this some valid programs are not accepted.

An example scenario of a valid program being declined is when you have a struct (let's call it `y`) inheriting from another struct with a name `x` but the struct `y` is in a namespace that is also called `x`:
```
struct x
{};

namespace
{
    namespace x
    {
        struct y : x
        {};
    }
}
```

This shall be accepted because: 
```
C++ [class.derived]p2 (wrt lookup in a base-specifier): The lookup for
  // the component name of the type-name or simple-template-id is type-only.
```



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