[clang] [Clang] Fix the trailing comma regression (PR #136273)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Younan Zhang (zyn0217)

<details>
<summary>Changes</summary>

925e195 introduced a regression since which we started to accept invalid trailing commas in many expression lists where they're not allowed by the grammar. The issue came from the fact that an additional invalid state - previously handled by ParseExpressionList - was overlooked in that patch.

Fixes https://github.com/llvm/llvm-project/issues/136254

No release entry because I want to backport it.

---
Full diff: https://github.com/llvm/llvm-project/pull/136273.diff


2 Files Affected:

- (modified) clang/lib/Parse/ParseExpr.cpp (-3) 
- (modified) clang/test/Parser/recovery.cpp (+18) 


``````````diff
diff --git a/clang/lib/Parse/ParseExpr.cpp b/clang/lib/Parse/ParseExpr.cpp
index 0a22f7372a9f9..2282fbe04839e 100644
--- a/clang/lib/Parse/ParseExpr.cpp
+++ b/clang/lib/Parse/ParseExpr.cpp
@@ -2239,8 +2239,6 @@ Parser::ParsePostfixExpressionSuffix(ExprResult LHS) {
             if (PP.isCodeCompletionReached() && !CalledSignatureHelp)
               RunSignatureHelp();
             LHS = ExprError();
-          } else if (!HasError && HasTrailingComma) {
-            Diag(Tok, diag::err_expected_expression);
           } else if (LHS.isInvalid()) {
             for (auto &E : ArgExprs)
               Actions.CorrectDelayedTyposInExpr(E);
@@ -3750,7 +3748,6 @@ bool Parser::ParseExpressionList(SmallVectorImpl<Expr *> &Exprs,
     if (Tok.is(tok::r_paren)) {
       if (HasTrailingComma)
         *HasTrailingComma = true;
-      break;
     }
   }
   if (SawError) {
diff --git a/clang/test/Parser/recovery.cpp b/clang/test/Parser/recovery.cpp
index 2fce67a52c6b6..261f5dc99bad4 100644
--- a/clang/test/Parser/recovery.cpp
+++ b/clang/test/Parser/recovery.cpp
@@ -222,3 +222,21 @@ void k() {
   func(1, ); // expected-error {{expected expression}}
 }
 }
+
+namespace GH136254 {
+
+void call() {
+  [a(42, )]() {} (); // expected-error {{expected expression}}
+
+  int *b = new int(42, ); // expected-error {{expected expression}}
+
+  struct S {
+    int c;
+
+    S() : c(42, ) {} // expected-error {{expected expression}}
+  };
+
+  int d(42, ); // expected-error {{expected expression}}
+}
+
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/136273