From: Stefan Monnier<monnier@iro.umontreal.ca>
Cc:rahguzar@zohomail.eu,61098@debbugs.gnu.org,dgutov@yandex.ru
Date: Sun, 05 Feb 2023 10:19:24 -0500
I guess I don't understand what show-paren-local-mode does, then. Let
me explain my line of reasoning:
(define-minor-mode show-paren-local-mode
"Toggle `show-paren-mode' only in this buffer."
:variable ( show-paren-mode .
(lambda (val) (setq-local show-paren-mode val)))
(cond
((eq show-paren-mode (default-value 'show-paren-mode))
(unless show-paren-mode
(show-paren--delete-overlays))
(kill-local-variable 'show-paren-mode))
((not (default-value 'show-paren-mode))
;; Locally enabled, but globally disabled.
(show-paren-mode 1) ; Setup the timer.
(setq-default show-paren-mode nil) ; But keep it globally disabled.
)
(t ;; Locally disabled only.
(show-paren--delete-overlays))))
When I looked at the above function and stepped through it in the OP's
scenario, what I saw was that the 2nd condition of 'cond' doesn't
fire, because the default-value of show-paren-mode is t nowadays. So
I concluded that this code relies on the mode being globally off by
default, and attempted to fix the condition that turns the mode on
locally even though it is on globally.
But if the mode is already globally enabled, the (setq-default show-paren-mode
nil)
will definitely not be right: you'd end up disabling it globally (while
maybe keeping it enabled locally).
The predicate used by the timer requires either a match of the buffer
(which doesn't happen in this case) or that the local value of
show-paren-mode is non-nil. Setting the local value non-nil is the
job of the mode function, isn't it?
Yes, but the first branch of the `cond` incorrectly does
`kill-local-variable` under the assumption that the local value doesn't
matter if it's the same as the global one, but that's not true here
because (as a wise man said):
The predicate used by the timer requires either a match of the buffer
(which doesn't happen in this case) or that the local value of
show-paren-mode is non-nil.