[Bug c++/95789] [10/11 Regression] Const method is allowed to return non-const reference on template class

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95789

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |10.2
                 CC|                            |jakub at gcc dot gnu.org
            Summary|Const method is allowed to  |[10/11 Regression] Const
                   |return non-const reference  |method is allowed to return
                   |on template class           |non-const reference on
                   |                            |template class
           Keywords|                            |accepts-invalid
   Last reconfirmed|                            |2020-06-21
             Status|UNCONFIRMED                 |NEW
      Known to fail|                            |10.1.0, 11.0
     Ever confirmed|0                           |1
      Known to work|                            |9.3.0

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
struct B {
    int n;
};

template <typename T>
struct A {
    B& get() const { return f; }

    B f;
};

int main() {
    A<int> a;
    a.f = {};

    a.get().n = 10;
    if (a.f.n != 0)
      __builtin_abort();
}

Started with r10-7094

    c++: Readd [LR]ROTATE_EXPR support to constexpr.c [PR94067]

    Since r10-6527-gaaa26bf496a646778ac861aed124d960b5bf549f fold_for_warn
    will perform maybe_constant_value even on some cp_fold produced trees and
    so can include rotate exprs which were removed last fall from constexpr.c

    2020-03-09  Jakub Jelinek  <jakub@redhat.com>

            PR c++/94067
            Revert
            2019-10-11  Paolo Carlini  <paolo.carlini@oracle.com>

            * constexpr.c (cxx_eval_constant_expression): Do not handle
            RROTATE_EXPR and LROTATE_EXPR.

            * g++.dg/warn/Wconversion-pr94067.C: New test.