[Clang] Fix crash on improper use of __array_extent

clang/docs/ReleaseNotes.rst

@@ -823,6 +823,7 @@ Bug Fixes to C++ Support
   differering by their constraints when only one of these function was variadic.
 - Fix a crash when a variable is captured by a block nested inside a lambda. (Fixes #GH93625).
 - Fixed a type constraint substitution issue involving a generic lambda expression. (#GH93821)
+- Fix a crash caused by improper use of ``__array_extent``. (#GH80474)
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^

clang/lib/Parse/ParseExprCXX.cpp

@@ -4011,6 +4011,9 @@ ExprResult Parser::ParseArrayTypeTrait() {
     ExprResult DimExpr = ParseExpression();
     T.consumeClose();
 
+    if (DimExpr.isInvalid())
+      return ExprError();
+
     return Actions.ActOnArrayTypeTrait(ATT, Loc, Ty.get(), DimExpr.get(),
                                        T.getCloseLocation());
   }

clang/test/SemaCXX/incomplete-array-extent.cpp

@@ -0,0 +1,5 @@
+// RUN: %clang_cc1 -verify -std=c++14 %s
+
+auto f() {
+  return __array_extent(int, ); // expected-error {{expected expression}}
+}