[clang][Parser] Fix crash on invalid attribute in constexpr function

Author: el-ev

clang/lib/Parse/ParseDeclCXX.cpp

@@ -760,6 +760,10 @@ Parser::DeclGroupPtrTy Parser::ParseUsingDeclaration(
 
     Decl *AD = ParseAliasDeclarationAfterDeclarator(
         TemplateInfo, UsingLoc, D, DeclEnd, AS, Attrs, &DeclFromDeclSpec);
+
+    if (!AD)
+      return nullptr;
+
     return Actions.ConvertDeclToDeclGroup(AD, DeclFromDeclSpec);
   }
 

clang/test/Parser/cxx-invalid-attr-in-constexpr-crash.cpp

@@ -0,0 +1,8 @@
+// RUN: %clang_cc1 -fsyntax-only -verify %s
+
+// issue144264
+constexpr void test() 
+{ 
+    using TT = struct T[deprecated{}; 
+    // expected-error@-1 {{use of undeclared identifier 'deprecated'}}
+}