[Bug c++/71365] New: [7 Regression] g++ reject access to parent's parent virtual method

["zsojka at seznam dot cz" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71365

            Bug ID: 71365
           Summary: [7 Regression] g++ reject access to parent's parent
                    virtual method
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Keywords: rejects-valid
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: zsojka at seznam dot cz
  Target Milestone: ---
              Host: x86_64-pc-linux-gnu

Created attachment 38615
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=38615&action=edit
testcase (from openttd)

Compiler output:
$ g++ accept.C 
accept.C: In member function 'virtual void C<T>::foo()':
accept.C:7:55: error: 'A' is not a base of 'C<T>'
 class C : public B<T> { virtual void foo() { this->A::foo(); } };
                                                       ^~~
I think this code is valid, and it is accepted by all GCC versions up to 6.1.1.
If it is invalid, the error message should be improved to mention, for example,
"direct base". Note the code is accepted if B is not a template.