[Bug c++/113342] New: Template parameter does not shadow member enum value.

[Bug c++/113342] New: Template parameter does not shadow member enum value.

[courteauxmartijn at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113342

            Bug ID: 113342
           Summary: Template parameter does not shadow member enum value.
           Product: gcc
           Version: 13.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: courteauxmartijn at gmail dot com
  Target Milestone: ---

Consider the boolean template parameter named "GPU" (think: the "Ref"
references something on a GPU):


template<bool GPU>
struct Ref {};

struct Job{
    enum Device { CPU, GPU };

    template<bool GPU>
    void create(Ref<GPU> ref);
};

template<bool GPU>
void Job::create(Ref<GPU> ref) {}


The Job::Device enum has as second value "GPU". The implementation on the last
line of Job::create(Ref<GPU> ref) treats GPU as this second enum value, instead
of the boolean template argument. I believe the existence of the template
argument named "GPU" should shadow the enum value. However, the compiler
outputs this:

<source>:12:6: error: no declaration matches 'void Job::create(Ref<true>)'
   12 | void Job::create(Ref<GPU> ref) {}
      |      ^~~
<source>:8:10: note: candidate is: 'template<bool GPU> void
Job::create(Ref<GPU>)'
    8 |     void create(Ref<GPU> ref);
      |          ^~~~~~
<source>:4:8: note: 'struct Job' defined here
    4 | struct Job{
      |        ^~~

Notice in the first line that it treated the GPU as a "true", which would
originate from the fact that CPU has value 0, and GPU value 1 in that enum,
which gets converted to a bool implicitly.

https://godbolt.org/z/ro9hPvsz3

(Clang does compile this example as I expect it.)

[Bug c++/113342] Template parameter does not shadow member enum value.

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113342

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Note MSVC has the same behavior as GCC here:
```
<source>(13): error C2244: 'Job::create': unable to match function definition
to an existing declaration
<source>(13): note: see declaration of 'Job::create'
<source>(13): note: definition
<source>(13): note: 'void Job::create(Ref<true>)'
<source>(13): note: existing declarations
<source>(13): note: 'void Job::create(Ref<GPU>)'
```

This is most likely related to
https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2020/p1787r6.html paper.

[Bug c++/113342] Template parameter does not shadow member enum value.

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113342

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Note there was a change between `clang 10` and `clang 11` which changed clang
into accepting the code. So I am 99% sure it is that paper which caused the
change ...