[Bug c++/116379] [12/13/14/15 Regression] Type deduction error on decltype(auto) of parenthesized non-static data member since r12-5778

[cvs-commit at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116379

--- Comment #3 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The trunk branch has been updated by Marek Polacek <mpola...@gcc.gnu.org>:

https://gcc.gnu.org/g:b01664a6197f57615d3c62594037c575dfdd9035

commit r15-7527-gb01664a6197f57615d3c62594037c575dfdd9035
Author: Marek Polacek <pola...@redhat.com>
Date:   Thu Feb 13 15:56:16 2025 -0500

    c++: fix propagating REF_PARENTHESIZED_P [PR116379]

    Here we have:

      template<typename T>
      struct X{
          T val;
          decltype(auto) value(){
              return (val);
          }
      };

    where the return type of value should be 'int &' since '(val)' is an
    expression, not a name, and decltype(auto) performs the type deduction
    using the decltype rules.

    The problem is that we weren't propagating REF_PARENTHESIZED_P
    correctly: the return value of finish_non_static_data_member in this
    test was a REFERENCE_REF_P, so we didn't set the flag.  We should
    use force_paren_expr like below.

            PR c++/116379

    gcc/cp/ChangeLog:

            * pt.cc (tsubst_expr) <COMPONENT_REF>: Use force_paren_expr to set
            REF_PARENTHESIZED_P.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp1y/decltype-auto9.C: New test.

    Reviewed-by: Jason Merrill <ja...@redhat.com>