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

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.

Fixed: #113468

clang/docs/ReleaseNotes.rst

@@ -470,6 +470,7 @@ Bug Fixes in This Version
 - The warning emitted for an unsupported register variable type now points to
   the unsupported type instead of the ``register`` keyword (#GH109776).
 - Fixed a crash when emit ctor for global variant with flexible array init  (#GH113187).
+- Fixed a crash when GNU statement expression contains invalid statement (#GH113468).
 
 Bug Fixes to Compiler Builtins
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

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

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;
+}