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bug#61098: 29.0.60; Confusing behavior of show-paren-mode
From: |
Stefan Monnier |
Subject: |
bug#61098: 29.0.60; Confusing behavior of show-paren-mode |
Date: |
Sun, 05 Feb 2023 10:19:24 -0500 |
User-agent: |
Gnus/5.13 (Gnus v5.13) |
> 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.
-- Stefan