Question about existing tests for [dcl.stc]

[Aaron Ballman]

On Mon, May 19, 2014 at 5:32 PM, Richard Smith <richard at metafoo.co.uk> wrote:
> You're citing the wrong section of the standard in your patch. The relevant
> wording is [dcl.stc]p1: "If a storage-class-specifier appears in a
> decl-specifier-seq, [...] the init-declarator-list of the declaration shall
> not be empty [...]."

Ah, good to know. I made it down to p9 because we were declaring a
type instead of a member variable, but that makes sense.

> Do we really need to change the code here? Is the new diagnostic better than
> the old one?

Old diagnostic: ext-warn "'mutable' is not permitted on a declaration of a type"
Proposed diagnostic: error "'mutable' can only be applied to member variables"

Honestly, either works for me in terms of wording.

> Do we have a reason to promote this from ExtWarn to Error just
> for mutable and not for other storage class specifiers?

I was going with error because the other mutable constraint violations
are also errors (including this existing one which I was reusing).
Also, it seems weird to treat this as an extension -- what does this
extension actually provide in terms of benefit for the mutable
keyword? What does a mutable type declaration even mean?

~Aaron