[Bug c++/113153] New: suboptimal error message when using reserved identifier

[Bug c++/113153] New: suboptimal error message when using reserved identifier

[michael.kenzel at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113153

            Bug ID: 113153
           Summary: suboptimal error message when using reserved
                    identifier
           Product: gcc
           Version: 13.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: michael.kenzel at gmail dot com
  Target Milestone: ---

When using a keyword as the name of an enum, gcc will issue a diagnostic about
the enum being "unnamed". This can be very confusing:

    enum class register { rax, rcx, rdx, rbx };

compiled with -std=c++23 produces

error: unnamed scoped enum is not allowed
    1 | enum class register {};
      |            ^~~~~~~~
warning: elaborated-type-specifier for a scoped enum must not use the 'class'
keyword
    1 | enum class register {};
      | ~~~~ ^~~~~
      |      -----
error: expected identifier before 'register'
    1 | enum class register {};
      |            ^~~~~~~~
error: expected unqualified-id before '{' token
    1 | enum class register {};
      |                     ^

https://godbolt.org/z/s1ocevaWe

[Bug c++/113153] suboptimal error message when using reserved identifier

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113153

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |enhancement

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed.


Note clang is just as bad:
```
<source>:1:16: error: expected identifier or '{'
    1 |     enum class register { rax, rcx, rdx, rbx };
      |                ^
1 error generated.
```

EDG/ICC is slightly better:
```
<source>(1): error: expected an identifier
      enum class register { rax, rcx, rdx, rbx };
                 ^
```

MSVC is bad too:
```
<source>(1): error C2332: 'enum': missing tag name
<source>(1): error C2059: syntax error: 'function-style cast'
<source>(1): error C2143: syntax error: missing ';' before '{'
<source>(1): error C2447: '{': missing function header (old-style formal list?)
```

[Bug c++/113153] suboptimal error message when using reserved identifier

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113153

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
If you remove the class, GCC has a decent error message:
```
<source>:1:11: error: expected identifier before 'register'
    1 |     enum  register { rax, rcx, rdx, rbx };
      |           ^~~~~~~~
```

[Bug c++/113153] suboptimal error message when using reserved identifier and `enum class`

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113153

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
            Summary|suboptimal error message    |suboptimal error message
                   |when using reserved         |when using reserved
                   |identifier                  |identifier and `enum class`
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2023-12-27

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
.