[Bug c++/105734] New: Regression: Incorrect "error: invalid use of 'auto'"

[Bug c++/105734] New: Regression: Incorrect "error: invalid use of 'auto'"

[llvm at rifkin dot dev]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105734

            Bug ID: 105734
           Summary: Regression: Incorrect "error: invalid use of 'auto'"
           Product: gcc
           Version: 12.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: llvm at rifkin dot dev
  Target Milestone: ---

The following code errors erroneously: https://godbolt.org/z/68vYYj8cc

A more minimal reproducible example is here: https://godbolt.org/z/f75Yx7K57.
Interestingly the error only manifests in conjunction with the explicit
destructor call.

This came up in conjunction with a library doing a lot of TMP shenanigans, I
will try to make a more minimal standalone reproducible example.

[Bug c++/105734] Regression: Incorrect "error: invalid use of 'auto'"

[llvm at rifkin dot dev]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105734

--- Comment #1 from Jeremy R. <llvm at rifkin dot dev> ---
More minimal: https://godbolt.org/z/WcGab4W8T

[Bug c++/105734] Regression: Incorrect "error: invalid use of 'auto'"

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105734

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Reduced testcase:
namespace hh {
    struct nothing {};
    template<typename A = int>
    struct expression_decomposer {
        auto h()  {
            return expression_decomposer<bool>();
        }
    };
}

template <typename T>
void bar() {
        auto m = hh::expression_decomposer( hh::expression_decomposer{}.h());
        m.~expression_decomposer();
}

void foo() { bar<int>(); }

[Bug c++/105734] Regression: Incorrect "error: invalid use of 'auto'"

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105734

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #2)
> Reduced testcase:
> namespace hh {
>     struct nothing {};
>     template<typename A = int>
>     struct expression_decomposer {
>         auto h()  {
>             return expression_decomposer<bool>();
>         }
>     };
> }
> 
> template <typename T>
> void bar() {
>         auto m = hh::expression_decomposer( hh::expression_decomposer{}.h());
>         m.~expression_decomposer();
> }
> 
> void foo() { bar<int>(); }

The namespace is really required here. If I remove it, it works ...

[Bug c++/105734] [12/13 Regression]: Incorrect "error: invalid use of 'auto'" for explicit destructor inside a template

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105734

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |12.2
            Summary|Regression: Incorrect       |[12/13 Regression]:
                   |"error: invalid use of      |Incorrect "error: invalid
                   |'auto'"                     |use of 'auto'" for explicit
                   |                            |destructor inside a
                   |                            |template
      Known to fail|                            |12.1.0
      Known to work|                            |11.3.0
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2022-05-26

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed.

[Bug c++/105734] [12/13 Regression]: Incorrect "error: invalid use of 'auto'" for explicit destructor inside a template

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105734

--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Jeremy R. from comment #1)
> More minimal: https://godbolt.org/z/WcGab4W8T

>// only fails when this stuff is in a namespace, for some reason

You found that at the same time I did :).

Here is the most reduced testcase changing the names some more:
namespace hh {
    struct nothing {};
    template<typename A = int>
    struct s {
        auto h()  {
            return s<bool>();
        }
    };
}

template <typename T>
void bar() {
        auto m = hh::s( hh::s{}.h());
        m.~s();
}

void foo() { bar<int>(); }

[Bug c++/105734] [12/13 Regression]: Incorrect "error: invalid use of 'auto'" for explicit destructor inside a template

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105734

--- Comment #6 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
A little more reduced:
namespace hh {
    struct nothing {};
    template<int = 1>
    struct s {
        s h();
    };
}

template <int>
void bar() {
        auto m = hh::s(hh::s{}.h());
        m.~s();
}
void foo() { bar<1>(); }

The template arguments can be the same even.

[Bug c++/105734] [12/13 Regression]: Incorrect "error: invalid use of 'auto'" for explicit destructor inside a template

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105734

--- Comment #7 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Jeremy R. from comment #1)
> More minimal: https://godbolt.org/z/WcGab4W8T

The https://gcc.gnu.org/bugs very clearly says to provide the testcase *here*
not only as a URL.

[Bug c++/105734] [12/13 Regression]: Incorrect "error: invalid use of 'auto'" for explicit destructor inside a template

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105734

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jason at gcc dot gnu.org

--- Comment #8 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Regression started with r12-3643

 c++: improve lookup of member-qualified names

[Bug c++/105734] [12/13 Regression]: Incorrect "error: invalid use of 'auto'" for explicit destructor inside a template

[llvm at rifkin dot dev]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105734

--- Comment #9 from Jeremy R. <llvm at rifkin dot dev> ---
(In reply to Jonathan Wakely from comment #7)
> (In reply to Jeremy R. from comment #1)
> > More minimal: https://godbolt.org/z/WcGab4W8T
> 
> The https://gcc.gnu.org/bugs very clearly says to provide the testcase
> *here* not only as a URL.

Thanks for letting me know

[Bug c++/105734] [12/13 Regression]: Incorrect "error: invalid use of 'auto'" for explicit destructor inside a template

[llvm at rifkin dot dev]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105734

--- Comment #10 from Jeremy R. <llvm at rifkin dot dev> ---
One workaround in the general case is
decltype(ns::expression_decomposer(ns::expression_decomposer{} << expr)) =
libassert_decomposer = ns::expression_decomposer(ns::expression_decomposer{} <<
expr);

But this doesn't work if expr is a lambda.

A more general workaround is deferring the destructor to another function:

template<typename T> void destruct(T& t) {
    t.~T();
}
template <int>
void bar() {
    auto m = hh::s(hh::s{}.h());
    destruct(m);
}

[Bug c++/105734] [12/13 Regression]: Incorrect "error: invalid use of 'auto'" for explicit destructor inside a template

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105734

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P2

[Bug c++/105734] [12/13 Regression]: Incorrect "error: invalid use of 'auto'" for explicit destructor inside a template

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105734

Jason Merrill <jason at gcc dot gnu.org> changed:

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

[Bug c++/105734] [12/13 Regression]: Incorrect "error: invalid use of 'auto'" for explicit destructor inside a template

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105734

--- Comment #11 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jason Merrill <jason@gcc.gnu.org>:

https://gcc.gnu.org/g:e2e471d83d16449a325315c0f33dc52b90ce0fac

commit r13-920-ge2e471d83d16449a325315c0f33dc52b90ce0fac
Author: Jason Merrill <jason@redhat.com>
Date:   Tue May 31 16:31:35 2022 -0400

    c++: auto and dependent member name [PR105734]

    In r12-3643 I improved our handling of type names after . or -> when
    unqualified lookup doesn't find anything, but it needs to handle auto
    specially.

            PR c++/105734

    gcc/cp/ChangeLog:

            * parser.cc (cp_parser_postfix_dot_deref_expression): Use typeof
            if the expression has auto type.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp0x/auto57.C: New test.

[Bug c++/105734] [12/13 Regression]: Incorrect "error: invalid use of 'auto'" for explicit destructor inside a template

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105734

--- Comment #12 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-12 branch has been updated by Jason Merrill
<jason@gcc.gnu.org>:

https://gcc.gnu.org/g:b090938e61260ce841a0d51de3407881a38e3c52

commit r12-8447-gb090938e61260ce841a0d51de3407881a38e3c52
Author: Jason Merrill <jason@redhat.com>
Date:   Tue May 31 16:31:35 2022 -0400

    c++: auto and dependent member name [PR105734]

    In r12-3643 I improved our handling of type names after . or -> when
    unqualified lookup doesn't find anything, but it needs to handle auto
    specially.

            PR c++/105734

    gcc/cp/ChangeLog:

            * parser.cc (cp_parser_postfix_dot_deref_expression): Use typeof
            if the expression has auto type.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp0x/auto57.C: New test.

[Bug c++/105734] [12/13 Regression]: Incorrect "error: invalid use of 'auto'" for explicit destructor inside a template

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105734

Jason Merrill <jason at gcc dot gnu.org> changed:

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

--- Comment #13 from Jason Merrill <jason at gcc dot gnu.org> ---
Fixed for 12.2/13.

[Bug c++/105734] [12/13 Regression]: Incorrect "error: invalid use of 'auto'" for explicit destructor inside a template

[llvm at rifkin dot dev]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105734

--- Comment #14 from Jeremy R. <llvm at rifkin dot dev> ---
Thank you for the quick patch :)