[clang] [Clang] Avoid assertion failure for initialized extern aliases (PR #223124)

[via cfe-commits]

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@@ -14127,6 +14093,15 @@ void Sema::AddInitializerToDecl(Decl *RealDecl, Expr *Init, bool DirectInit) {
     return;
   }
 
+  // handleAliasAttr() runs before the initializer is attached to the VarDecl,
+  // so it cannot determine that an extern declaration with an initializer is a
+  // definition. Diagnose the conflict now that an initializer is present and
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keepyixiao wrote:


I have a question I'd like to ask about the following case:

```cpp
int v1;

struct S {
  static int i __attribute__((alias("v1")));
};

int S::i = 12;
```

Should

```static int i __attribute__((alias("v1")));```

be considered a definition or merely a declaration here?

According to the standard C++ rules, an in-class declaration of a non-inline static data member is normally not a definition.

However, under the semantics of the alias extension, the alias declaration itself appears to define the corresponding symbol.

So I'm a little unsure how this declaration should be classified in this case.

https://github.com/llvm/llvm-project/pull/223124