[clang] [Sema] Diagnose use of if/else-if condition variable inside else-if/else branch(s) (PR #156436)

[Erich Keane via cfe-commits]

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@@ -1570,6 +1564,12 @@ class Sema final : public SemaBase {
   Sema(const Sema &) = delete;
   void operator=(const Sema &) = delete;
 
+  /// Tracks condition variables declared in `if` statements,
+  /// mapping each VarDecl to the `Scope*` where it was created.
+  /// Used to detect references to these variables outside their
+  /// lifetime (e.g. in the `else` branch or after the `if`).
+  llvm::DenseMap<const VarDecl*, Scope*> IfScopeVars;
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erichkeane wrote:

This shouldn't live in Sema, the Scope itself should have a reference to the var.

https://github.com/llvm/llvm-project/pull/156436