[Bug c++/99610] New: GCC thinks member function template is a deduction guide

[Bug c++/99610] New: GCC thinks member function template is a deduction guide

[gcchelp.5.adept at 0sg dot net]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99610

            Bug ID: 99610
           Summary: GCC thinks member function template is a deduction
                    guide
           Product: gcc
           Version: 8.4.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gcchelp.5.adept at 0sg dot net
  Target Milestone: ---

When compiling with -std=c++17 or -std=gnu++17,
the following errors are reported for the code below:

[2] error: return type specified for deduction guide
[2] error: decl-specifier in declaration of deduction guide
[2] error: 'signed' or 'unsigned' invalid for '__dguide_Hash'
[2] error: deduction guide for 'Hash<K, V, C>' must have trailing return type
[1] note: 'template<class K, class V, class C> class Hash' declared here

The same code is accepted without errors by clang and msvc 2019.
I'm not sufficiently versed in the c++ standard to tell if this is on the
compiler or not.

Thanks!


---------------------- 

[1] template< typename K, typename V, typename C = HashContext<K> >
    class Hash 
    {
        // ...
    };


    template< typename K >
    class HashContext
    {
    public:
        template< typename X >
[2]     unsigned Hash( const X &arg ) const
            { ... }
    };

[Bug c++/99610] GCC thinks member function template is a deduction guide

[gcchelp.5.adept at 0sg dot net]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99610

--- Comment #1 from Christian Schüler <gcchelp.5.adept at 0sg dot net> ---
There is a workaround
declaring the function Hash with trailing return will make the error go away.

    template< typename X >
    auto Hash( const X &arg ) const -> unsigned
         { ... }

[Bug c++/99610] GCC thinks member function template is a deduction guide

[gcchelp.5.adept at 0sg dot net]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99610

--- Comment #2 from Christian Schüler <gcchelp.5.adept at 0sg dot net> ---
gcc version 8.4.0 (Ubuntu 8.4.0-1ubuntu1~18.04)

[Bug c++/99610] GCC thinks member function template is a deduction guide

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99610

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |rejects-valid
             Status|UNCONFIRMED                 |WAITING
   Last reconfirmed|                            |2021-03-16
     Ever confirmed|0                           |1

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
> clang++-9 -S t.C
t.C:1:48: error: no template named 'HashContext'
template< typename K, typename V, typename C = HashContext<K> >
                                               ^
t.C:14:15: error: expected expression
            { ... }
              ^

can you provide a complete testcase?

[Bug c++/99610] GCC thinks member function template is a deduction guide

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99610

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

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

--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Without a full testcase hard to say, but perhaps dup of PR97663?

[Bug c++/99610] GCC thinks member function template is a deduction guide

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99610

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
And if that is the case, there is also easy workaround, just use unsigned int
Hash instead of unsigned Hash.