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

[via cfe-commits]

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@@ -971,6 +971,35 @@ StmtResult Sema::ActOnIfStmt(SourceLocation IfLoc,
   if (!ConstevalOrNegatedConsteval && !elseStmt)
     DiagnoseEmptyStmtBody(RParenLoc, thenStmt, diag::warn_empty_if_body);
 
+  // Checks for if condition variable usage in else scope
+  if (elseStmt) {
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arrowten wrote:

@erichkeane Please take look at the changes. Let me know if this can be considered.

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