Re: master 5ee4209f30: cl-typep: Emit warning when using a type not known to be a type

[Basil L. Contovounesios]

Stefan Monnier [2022-06-06 00:04 -0400] wrote:

> branch: master
> commit 5ee4209f307fdf8cde9775539c9596d29edccd6d
> Author: Stefan Monnier <monnier@iro.umontreal.ca>
> Commit: Stefan Monnier <monnier@iro.umontreal.ca>
>
>     cl-typep: Emit warning when using a type not known to be a type
>     
>     `cl-typep` has used a heuristic that if there's a `<foo>-p` function,
>     then <foo> can be used as a type.  This made sense in the past where
>     most types were not officially declared to be (cl-)types, but nowadays
>     this just encourages abuses such as using `cl-typecase` with
>     "types" like `fbound`.  It's also a problem for EIEIO objects, where
>     for historical reasons `<foo>-p` tests if the object is of type
>     exactly `<foo>` whereas (cl-typep OBJ <foo>) should instead test
>     if OBJ is a *subtype* of `<foo>`.
>     
>     So we change `cl-typep` to emit a warning whenever this "-p" heuristic
>     is used, to discourage abuses, encourage the use of explicit
>     `cl-deftype` declarations, and try and detect some misuses of
>     `<foo>-p` for EIEIO objects.

[...]

I think this change gave rise to the following 'error: success' message:

0. emacs -Q -l cl-lib
1. (cl-typep (make-process :name "" :command '("true")) 'process)
2. C-j
   -| Warning: Unknown type: process
   => t

In practice, I see this when using Magit with Forge[0]; see the attached
backtrace which I obtained by adding a call to backtrace before
macroexp-warn-and-return in cl-typep.

Is the following a sufficient fix?

diff --git a/lisp/emacs-lisp/cl-macs.el b/lisp/emacs-lisp/cl-macs.el
index ada4f0344d..24a4cec4e2 100644
--- a/lisp/emacs-lisp/cl-macs.el
+++ b/lisp/emacs-lisp/cl-macs.el
@@ -3423,6 +3423,7 @@ cl--macroexp-fboundp
                  (null         . null)
                  (overlay      . overlayp)
                  (real         . numberp)
+                 (process      . processp)
                  (sequence     . sequencep)
                  (subr         . subrp)
                  (string       . stringp)

Thanks,

-- 
Basil

[0]: https://magit.vc/manual/forge/

forge-backtrace.txt
Description: Text document