[clang] [sema] enhance error handling for compound stmt body in `StmtExpr` (PR #113760)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Congcong Cai (HerrCai0907)

<details>
<summary>Changes</summary>

Mark the whole StmtExpr invalid when the last statement in compound statement is invalid.
Because the last statement need to do copy initialization, it causes subsequent errors to simply ignore last invalid statement.


---
Full diff: https://github.com/llvm/llvm-project/pull/113760.diff


2 Files Affected:

- (modified) clang/lib/Parse/ParseStmt.cpp (+9) 
- (added) clang/test/SemaCXX/gh113468.cpp (+12) 


``````````diff
diff --git a/clang/lib/Parse/ParseStmt.cpp b/clang/lib/Parse/ParseStmt.cpp
index 60d647da48f053..6d0de38095b999 100644
--- a/clang/lib/Parse/ParseStmt.cpp
+++ b/clang/lib/Parse/ParseStmt.cpp
@@ -1243,6 +1243,7 @@ StmtResult Parser::ParseCompoundStatementBody(bool isStmtExpr) {
       ParsedStmtContext::Compound |
       (isStmtExpr ? ParsedStmtContext::InStmtExpr : ParsedStmtContext());
 
+  bool LastIsError = false;
   while (!tryParseMisplacedModuleImport() && Tok.isNot(tok::r_brace) &&
          Tok.isNot(tok::eof)) {
     if (Tok.is(tok::annot_pragma_unused)) {
@@ -1299,7 +1300,15 @@ StmtResult Parser::ParseCompoundStatementBody(bool isStmtExpr) {
 
     if (R.isUsable())
       Stmts.push_back(R.get());
+    LastIsError = R.isInvalid();
   }
+  // StmtExpr needs to do copy initialization for last statement.
+  // If last statement is invalid, the last statement in `Stmts` will be
+  // incorrect. Then the whole compound statement should also be marked as
+  // invalid to prevent subsequent errors.
+  if (isStmtExpr && LastIsError && !Stmts.empty())
+    return StmtError();
+
   // Warn the user that using option `-ffp-eval-method=source` on a
   // 32-bit target and feature `sse` disabled, or using
   // `pragma clang fp eval_method=source` and feature `sse` disabled, is not
diff --git a/clang/test/SemaCXX/gh113468.cpp b/clang/test/SemaCXX/gh113468.cpp
new file mode 100644
index 00000000000000..94551986b0efaa
--- /dev/null
+++ b/clang/test/SemaCXX/gh113468.cpp
@@ -0,0 +1,12 @@
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify %s
+
+constexpr int expr() {
+  if (({
+        int f;
+        f = 0;
+        if (f)
+          break; // expected-error {{'break' statement not in loop or switch statement}}
+      }))
+    return 2;
+  return 1;
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/113760