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

[Henrik G. Olsson via cfe-commits]

hnrklssn wrote:

What differentiates the DecompositionDecl such that we need to mark the decl invalid when there's an error in the RHS, while for other decls we don't? It seems inconsistent.

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