> Please find attached a proposal to improve error handling in
> `cl-types-of'.  Ultimately, I think you were right and it is better to
> simply report derived type errors to the caller and abort processing,
> but while also preventing their recurrence as much as possible :-)
> 
> So my proposal is to still handle any error on a derived type, in
> order to disable the type as is currently done by removing it from the
> list of types; but, instead of warn, raise a new `cl-type-error'
> mentioning the type in error and the underlying error.  Here are some
> simple examples for you to observe the result.
> 
> (cl-deftype T1 ()
>    '(satisfies plusp))
> 
> (cl-types-of -0.5)
> => (real float number number-or-marker atom t)
> 
> (cl-types-of 12)
> => (T1 real base-char character fixnum natnum integer number integer-or-marker number-or-marker atom t)
> 
> (cl-types-of "12")
> => Error on derived type: T1, (wrong-type-argument number-or-marker-p "12")
> 
> (cl-deftype T2 ()
>    `(satisfies ,(lambda (o) (memq 'T1 (cl-types-of o)))))
> 
> (cl-types-of "12")
> => Error on derived type: T2, (excessive-lisp-nesting 1601)
> 
> Does it make sense?

Please find attached a better patch, and a possible change log below.
Thanks
David

2025-05-19  David Ponce  <da_vid@orange.fr>

	Signal a `cl-type-error' instead of warning when a derived type
	encounters an error.

	* lisp/emacs-lisp/cl-extra.el (cl-type-error): New error symbol.
	(cl-types-of): Use it.