[C++ Patch] PR 89875 ("[7/8/9/10 Regression] invalid typeof reference to a member of an incomplete struct accepted at function scope")

[Paolo Carlini]

Hi,

a while ago Martin noticed that an unintended consequence of an old 
tweak of mine - which avoided redundant error messages emitted from 
cp_parser_init_declarator - is that, in some cases, we started accepting 
ill-formed typeofs. Luckily, decltype isn't affected and that points to 
the real issue: by the time that place in cp_parser_init_declarator is 
reached, for a decltype version we already emitted a correct error 
message. Thus I think the right way to fix the problem is simply 
committing to tentative parse when, toward the end of 
cp_parser_sizeof_operand we know that we must be looking at a (possibly 
ill-formed) expression. Tested x86_64-linux.

Thanks, Paolo.

///////////////////////////

/cp
2019-05-10  Paolo Carlini  <paolo.carl...@oracle.com>

        PR c++/89875
        * parser.c (cp_parser_sizeof_operand): When the type-id production
        did not work out commit to the tentative parse.

/testsuite
2019-05-10  Paolo Carlini  <paolo.carl...@oracle.com>

        PR c++/89875
        * g++.dg/cpp0x/decltype-pr66548.C: Remove xfail.
        * g++.dg/template/sizeof-template-argument.C: Adjust expected error.
Index: cp/parser.c
===================================================================
--- cp/parser.c (revision 271059)
+++ cp/parser.c (working copy)
@@ -28998,7 +28998,11 @@ cp_parser_sizeof_operand (cp_parser* parser, enum
   /* If the type-id production did not work out, then we must be
      looking at the unary-expression production.  */
   if (!expr)
-    expr = cp_parser_unary_expression (parser);
+    {
+      cp_parser_commit_to_tentative_parse (parser);
+      
+      expr = cp_parser_unary_expression (parser);
+    }
 
   /* Go back to evaluating expressions.  */
   --cp_unevaluated_operand;
Index: testsuite/g++.dg/cpp0x/decltype-pr66548.C
===================================================================
--- testsuite/g++.dg/cpp0x/decltype-pr66548.C   (revision 271059)
+++ testsuite/g++.dg/cpp0x/decltype-pr66548.C   (working copy)
@@ -11,7 +11,7 @@ struct Meow {};
 
 void f ()
 {
-  decltype (Meow.purr ()) d;   // { dg-error "expected primary-expression" 
"pr89875" { xfail c++98_only } }
+  decltype (Meow.purr ()) d;   // { dg-error "expected primary-expression" }
   (void)&d;
 }
 
Index: testsuite/g++.dg/template/sizeof-template-argument.C
===================================================================
--- testsuite/g++.dg/template/sizeof-template-argument.C        (revision 
271059)
+++ testsuite/g++.dg/template/sizeof-template-argument.C        (working copy)
@@ -3,9 +3,9 @@
 
 template<int> struct A {};
 
-template<typename> struct B : A <sizeof(=)> {}; /* { dg-error "template 
argument" } */
+template<typename> struct B : A <sizeof(=)> {}; /* { dg-error "expected 
primary-expression" } */
 
-template<typename> struct C : A <sizeof(=)> {}; /* { dg-error "template 
argument" } */
+template<typename> struct C : A <sizeof(=)> {}; /* { dg-error "expected 
primary-expression" } */
 
 int a;