bug#57915: 29.0.50; Misleading warning about use of quote in clause of cl-case

bug#57915: 29.0.50; Misleading warning about use of quote in clause of cl-case

[Jonas Bernoulli]

I inherited some code like this:

  (cl-case foo
    ((quote) ...)
    ((funcall) ...))

While I probably would not have written it like this, I think it
makes sense, since (quote ...) looks like ... is being quoted.  Using
((quote) ...) make it clear to the human reader that that is not what is
happening.  Unfortunately the byte-compiler now provides this misleading
warning:

  Warning: Case (quote) will match ‘quote’.  If that’s intended,
    write (nil quote) instead.  Otherwise, don’t quote ‘nil’.

This is misleading because the conditions (quote) and (nil quote) are
not equivalent; obviously the first only matches `quote', while second
also matches nil.  I have seen this exact warning for a few other
packages and fear that someone might blindly follow the suggestion.

Could this special case, (quote), be handled differently?  I understand
we want to catch, pcase-inspired clauses like 'x.  I am not sure we can
tell the difference between (quote), (quote nil) and 'nil, but it seems
to me, that if that is not the case, we should avoid the invalid
recommendation at the cost of not warning about the other, likely
unintended uses.

    Cheers,
    Jonas

bug#57915: 29.0.50; Misleading warning about use of quote in clause of cl-case

[Lars Ingebrigtsen]

Jonas Bernoulli <jonas@bernoul.li> writes:

> I inherited some code like this:
>
>   (cl-case foo
>     ((quote) ...)
>     ((funcall) ...))
>
> While I probably would not have written it like this, I think it
> makes sense, since (quote ...) looks like ... is being quoted.  Using
> ((quote) ...) make it clear to the human reader that that is not what is
> happening.  Unfortunately the byte-compiler now provides this misleading
> warning:
>
>   Warning: Case (quote) will match ‘quote’.  If that’s intended,
>     write (nil quote) instead.  Otherwise, don’t quote ‘nil’.

[...]

> Could this special case, (quote), be handled differently?  I understand
> we want to catch, pcase-inspired clauses like 'x.  I am not sure we can
> tell the difference between (quote), (quote nil) and 'nil, but it seems
> to me, that if that is not the case, we should avoid the invalid
> recommendation at the cost of not warning about the other, likely
> unintended uses.

Yeah, since there isn't really any other way to express this (or is
there?), we should probably not warn about this construction.

I've added Philipp to the CCs; perhaps he has some comments.

bug#57915: 29.0.50; Misleading warning about use of quote in clause of cl-case

[Philipp Stephani via Bug reports for GNU Emacs, the Swiss army knife of text editors]

On Mon, 19 Sept 2022 at 10:32, Lars Ingebrigtsen <larsi@gnus.org> wrote:
>
> Jonas Bernoulli <jonas@bernoul.li> writes:
>
> > I inherited some code like this:
> >
> >   (cl-case foo
> >     ((quote) ...)
> >     ((funcall) ...))
> >
> > While I probably would not have written it like this, I think it
> > makes sense, since (quote ...) looks like ... is being quoted.  Using
> > ((quote) ...) make it clear to the human reader that that is not what is
> > happening.  Unfortunately the byte-compiler now provides this misleading
> > warning:
> >
> >   Warning: Case (quote) will match ‘quote’.  If that’s intended,
> >     write (nil quote) instead.  Otherwise, don’t quote ‘nil’.
>
> [...]
>
> > Could this special case, (quote), be handled differently?  I understand
> > we want to catch, pcase-inspired clauses like 'x.  I am not sure we can
> > tell the difference between (quote), (quote nil) and 'nil, but it seems
> > to me, that if that is not the case, we should avoid the invalid
> > recommendation at the cost of not warning about the other, likely
> > unintended uses.
>
> Yeah, since there isn't really any other way to express this (or is
> there?), we should probably not warn about this construction.
>
> I've added Philipp to the CCs; perhaps he has some comments.

Makes sense, fixed in commit a71de4b52d3de14349ded7d88c4cae6e2a9376ae.

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bug#57915: 29.0.50; Misleading warning about use of quote in clause of cl-case

[Lars Ingebrigtsen]

Philipp Stephani <phst@google.com> writes:

> Makes sense, fixed in commit a71de4b52d3de14349ded7d88c4cae6e2a9376ae.

Thanks; I can confirm that this fixes the problem, so I'm closing this
bug report.