[Bug c++/98515] New: Possible regression causing "is protected within this context" error

[Bug c++/98515] New: Possible regression causing "is protected within this context" error

[belegdol at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98515

            Bug ID: 98515
           Summary: Possible regression causing "is protected within this
                    context" error
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: belegdol at gmail dot com
  Target Milestone: ---

mame-0.227 has failed to compile with gcc-11 in Fedora 34 [1]
(gcc-11.0.0-0.11.fc34). mame developers have kindly provided a minimal test
case. This fails with gcc-11 but works on 

class A {
public:
    A() = default;

protected:
    int var0 = 0;
};

template<int a> class B : public A {
public:
    using A::A;
};

template<int a, int b> class C : public B<a> {
public:
    using B<a>::B;

    void g();
};

template<int a, int b> void C<a, b>::g()
{
    A::var0++;
}

template class C<0, 0>;

While this works:

class A {
public:
    A() = default;

protected:
    int var0 = 0;
};

template<int a> class B : public A {
public:
    using A::A;
};

template<int a, int b> class C : public B<a> {
public:
    using B<a>::B;

    void g() { A::var0++; }
};

template class C<0, 0>;

[1] https://github.com/mamedev/mame/issues/7616

[Bug c++/98515] Possible regression causing "is protected within this context" error

[belegdol at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98515

--- Comment #1 from Julian Sikorski <belegdol at gmail dot com> ---
Created attachment 49877
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=49877&action=edit
compiling test case

[Bug c++/98515] Possible regression causing "is protected within this context" error

[belegdol at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98515

--- Comment #2 from Julian Sikorski <belegdol at gmail dot com> ---
Created attachment 49878
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=49878&action=edit
failing test case

[Bug c++/98515] Possible regression causing "is protected within this context" error

[belegdol at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98515

--- Comment #3 from Julian Sikorski <belegdol at gmail dot com> ---
The initial comment meant to say: This fails with gcc-11 but works on gcc-10.2.

[Bug c++/98515] [11 Regression] Possible regression causing "is protected within this context" error

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98515

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |11.0
   Last reconfirmed|                            |2021-01-04
             Status|UNCONFIRMED                 |NEW
           Priority|P3                          |P1
     Ever confirmed|0                           |1
            Summary|Possible regression causing |[11 Regression] Possible
                   |"is protected within this   |regression causing "is
                   |context" error              |protected within this
                   |                            |context" error
           Keywords|                            |rejects-valid
                 CC|                            |mpolacek at gcc dot gnu.org,
                   |                            |ppalka at gcc dot gnu.org

--- Comment #4 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Confirmed.  Started with r11-1350.

[Bug c++/98515] [11 Regression] Possible regression causing "is protected within this context" error

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98515

Patrick Palka <ppalka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|unassigned at gcc dot gnu.org      |ppalka at gcc dot gnu.org
             Status|NEW                         |ASSIGNED

[Bug c++/98515] [11 Regression] Possible regression causing "is protected within this context" error

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98515

--- Comment #5 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Patrick Palka <ppalka@gcc.gnu.org>:

https://gcc.gnu.org/g:98a1fb705ead9258642f2dec0431f11508a9b13c

commit r11-6553-g98a1fb705ead9258642f2dec0431f11508a9b13c
Author: Patrick Palka <ppalka@redhat.com>
Date:   Fri Jan 8 10:02:04 2021 -0500

    c++: Fix access checking of scoped non-static member [PR98515]

    In the first testcase below, we incorrectly reject the use of the
    protected non-static member A::var0 from C<int>::g() because
    check_accessibility_of_qualified_id, at template parse time, determines
    that the access doesn't go through 'this'.  (This happens because the
    dependent base B<T> of C<T> doesn't have a binfo object, so it appears
    to DERIVED_FROM_P that A is not an indirect base of C<T>.)  From there
    we create the corresponding deferred access check, which we then
    perform at instantiation time and which (expectedly) fails.

    The problem ultimately seems to be that we can't in general determine
    whether a use of a scoped non-static member goes through 'this' until
    instantiation time, as the second testcase below illustrates.  So this
    patch makes check_accessibility_of_qualified_id punt in such situations
    to avoid creating a bogus deferred access check.

    gcc/cp/ChangeLog:

            PR c++/98515
            * semantics.c (check_accessibility_of_qualified_id): Punt if
            we're checking access of a scoped non-static member inside a
            class template.

    gcc/testsuite/ChangeLog:

            PR c++/98515
            * g++.dg/template/access32.C: New test.
            * g++.dg/template/access33.C: New test.

[Bug c++/98515] [11 Regression] Possible regression causing "is protected within this context" error

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98515

Patrick Palka <ppalka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|ASSIGNED                    |RESOLVED

--- Comment #6 from Patrick Palka <ppalka at gcc dot gnu.org> ---
This should now be fixed on trunk; thanks for the bug report.