[clang] [Clang][Parse] Fix crash on stmt-expr ending with 'extern void;' (PR #181579)

[Oliver Hunt via cfe-commits]

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@@ -1214,7 +1216,14 @@ StmtResult Parser::ParseCompoundStatementBody(bool isStmtExpr) {
 
     if (R.isUsable())
       Stmts.push_back(R.get());
-    LastIsError = R.isInvalid();
+    // Only treat the last statement as an error if an actual error diagnostic
+    // was emitted during parsing. Constructs like "extern void;" may produce
+    // an invalid StmtResult (via null DeclGroup) with only a warning, which
+    // should not cause the entire compound statement to fail in a stmt-expr.
+    // See https://github.com/llvm/llvm-project/issues/173921
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ojhunt wrote:

This comment is unnecessary, and reads like AI?

https://github.com/llvm/llvm-project/pull/181579