[clang] [clang][AST] Invalidate DecompositionDecl if it has invalid initializer. (PR #72428)

[Shafik Yaghmour via cfe-commits]

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@@ -13540,6 +13540,15 @@ void Sema::AddInitializerToDecl(Decl *RealDecl, Expr *Init, bool DirectInit) {
           CreateRecoveryExpr(Init->getBeginLoc(), Init->getEndLoc(), Args);
       if (RecoveryExpr.get())
         VDecl->setInit(RecoveryExpr.get());
+      // In general, for error recovery purposes, the initalizer doesn't play
+      // part in the valid bit of the declaration. There are a few exceptions:
+      //  1) if the var decl has a deduced auto type, and the type cannot be
+      //     deduced by an invalid initializer;
+      //  2) if the var decl is decompsition decl with a concrete type (e.g.
+      //    `int [a, b] = 1;`), and the initializer is invalid;
+      // Case 1) is already handled earlier in this function.
+      if (llvm::isa<DecompositionDecl>(VDecl)) // Case 2)
+        VDecl->setInvalidDecl();
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shafik wrote:

We should have the comment in both places. This is very helpful to understanding the code.

I agree that having the comment far away from the code that it is commenting on is less useful. The code could easily be moved in a refactor or in other ways and become completely disconnected. 

https://github.com/llvm/llvm-project/pull/72428