[Bug c++/96500] New: enum of underlying type bool do not

[Bug c++/96500] New: enum of underlying type bool do not

[fw at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96500

            Bug ID: 96500
           Summary: enum of underlying type bool do not
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Keywords: rejects-valid
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: fw at gcc dot gnu.org
  Target Milestone: ---

I believe this needs to be accepted:

enum E : bool { One, Two, Three };

See <http://eel.is/c++draft/dcl.enum#5>, “If the underlying type is fixed, the
type of each enumerator prior to the closing brace is the underlying type and
the constant-expression in the enumerator-definition shall be a converted
constant expression of the underlying type.”.

Converted constant expressions include integral conversions. Conversion from
int to bool is not a narrowing conversion.  So Three should have the value
true, just like Two.

[Bug c++/96500] enum of underlying type bool do not

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96500

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

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

--- Comment #1 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Note that here we don't have an enumerator-definition with " =
constant-expression" and that converted constant expressions don't allow
narrowing.

I'd much prefer if this was ill-formed, but probably at the moment it isn't.

[Bug c++/96500] enum of underlying type bool does not accept enumerators with integer constant values other than 0 and 1

[fw at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96500

Florian Weimer <fw at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |INVALID

--- Comment #2 from Florian Weimer <fw at gcc dot gnu.org> ---
I was wrong, conversions from int to bool are supposed to be narrowing, and Two
+ 1 has type int, and getting from there to bool is not permitted in a
converted constant expression.

I still have some concerns about narrowing conversions to bool, but those are
independent of the enum issue.