bug#54100: 29.0.50; Allow project-buffers to ignore some buffers

[Dmitry Gutov <dgutov@yandex.ru>]

On 24.02.2022 09:18, Manuel Uberti via Bug reports for GNU Emacs, the 
Swiss army knife of text editors wrote:
> Find attached yet a better approach to avoid repetition.

The patch looks good except for this part:

           (predicate
-          (lambda (buffer)
-            ;; BUFFER is an entry (BUF-NAME . BUF-OBJ) of Vbuffer_alist.
-            (memq (cdr buffer) buffers))))
+          (or predicate
+              (lambda (buffer)
+                ;; BUFFER is an entry (BUF-NAME . BUF-OBJ) of 
Vbuffer_alist.
+                (memq (cdr buffer) buffers)))))

Doesn't this mean that it won't do the (memq ... buffers) check and thus 
ignore the result of the (project-buffers pr) call?

Instead, it could be a lambda like

           (lambda (buffer)
             ;; BUFFER is an entry (BUF-NAME . BUF-OBJ) of Vbuffer_alist.
             (and (memq (cdr buffer) buffers)
                  (funcall predicate buffer)))

Does that make sense?

(I would also try to shorten the new defcustom's docstring by referring 
to the existing one, but I can make that change myself.)

> Note that the above mention problem about multiple conditions remains, 
> though. Help appreciated. :)

As described in the docstring:

   If any of these conditions are satisfied ...

So when you use this value

   '(mu-project-buffer-p
     (not (derived-mode . comint-mode)))

it means "either satisfies my-project-buffer-p or not derived from 
comint-mode". Whereas you probably wanted to combine them with "and":

   (setq-default project-switch-to-buffer-conditions
                 '(and mu-project-buffer-p
                       (not (derived-mode . comint-mode))))

And IDK, maybe the "and" top-level combination would work better for 
project-switch-to-buffer-conditions. It might trip up a user who's 
customizing both vars, though.

Or if you wanted to stay on "or" but make it easier for certain usage 
pattern, you could call the var 'project-ignore-buffer-conditions' (or 
"hide" or etc), and change its use appropriately. Then the value could 
contain

   '((not mu-project-buffer-p)
     (derived-mode . comint-mode))

...and (not mu-project-buffer-p) could obviously be rewritten in a 
negated way in the function's definition.