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From: Nicolas Goaziou <mail@HIDDEN>
To: 31361 <at> debbugs.gnu.org
Subject: Re: bug#31361: 25.3; Issue when advising `indent-line-function'
In-Reply-To: <87sh78phj1.fsf@HIDDEN> (Nicolas Goaziou's message of
"Thu, 03 May 2018 23:15:46 +0200")
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Content preview: Nicolas Goaziou <mail@HIDDEN> writes: > When
`indent-line-function'
is advised, using `add-function', and the > variable contains `indent-relative',
`indent-according-to-mode' has an > erratic behavior. > > In the following
code, from `indent-according-to-mode', > > (if (memq indent-line-function
> '(indent-relative indent-relative-maybe)) > ... > ;; The normal case. >
(funcall indent-line-function)) > > the if branch is no longer executed
because
`indent-line-function' is no > longer `indent-relative' but a closure around
it. [...]
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Cc: Stefan Monnier <monnier@HIDDEN>
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Nicolas Goaziou <mail@HIDDEN> writes:
> When `indent-line-function' is advised, using `add-function', and the
> variable contains `indent-relative', `indent-according-to-mode' has an
> erratic behavior.
>
> In the following code, from `indent-according-to-mode',
>
> (if (memq indent-line-function
> '(indent-relative indent-relative-maybe))
> ...
> ;; The normal case.
> (funcall indent-line-function))
>
> the if branch is no longer executed because `indent-line-function' is no
> longer `indent-relative' but a closure around it.
Thinking more about the problem, I think I can describe it differently.
When `indent-line-function' is set to `indent-relative' -- or
`indent-relative-maybe' -- the function `indent-relative' is not meant
to be actually called to handle the indentation. Instead, some ad-hoc
indentation is hard-coded into `indent-according-to-mode', which see.
However, when `indent-line-function' is advised, according to my
previous report, `indent-relative' is actually called for indentation,
which is not the intent, per above.
So basically, any call to `indent-according-to-mode', e.g., with
`reindent-then-newline-and-indent' or through Electric Indent mode, is
broken whenever `indent-relative' is advised.
One idea, suggested by Stefan, would be to write
`indent-according-to-mode' like the following:
(if (memq (advice--cd*r indent-line-function)
'(indent-relative indent-relative-maybe))
...
;; The normal case.
(funcall indent-line-function))
i.e., strip advices so that the ad-hoc code is executed, as intended,
instead of ultimately calling `indent-relative'. Unfortunately, this is
insufficient because the advices are not applied, which is also wrong.
If this stripping is done, it should also ensure that advices are
applied on the ad-hoc indentation code there.
FWIW, my gut feeling is that `indent-relative' -- and
`indent-relative-maybe' -- ought to be normalized to behave like
a normal indentation function, i.e., a function actually called from
`indent-according-to-mode'. This was the case before commit
a17b712b4d812d28086ae9af02f9043b36cf3e19 (Oct 30 2001).
Currently, `indent-relative' is two-sided. Therefore, the previous
suggestion might entail to split `indent-relative' into two parts, one
meant to be used as a value for `indent-line-function' -- maybe named
`indent-relative-function' -- and the other one to be used like current
`indent-relative', i.e., jumping from one indent point to the other.
bug-gnu-emacs@HIDDEN:bug#31361; Package emacs.
Full text available.
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for bug-gnu-emacs@HIDDEN; Thu, 03 May 2018 23:15:46 +0200
From: Nicolas Goaziou <mail@HIDDEN>
To: bug-gnu-emacs@HIDDEN
Subject: 25.3; Issue when advising `indent-line-function'
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Hello,
When `indent-line-function' is advised, using `add-function', and the
variable contains `indent-relative', `indent-according-to-mode' has an
erratic behavior.
In the following code, from `indent-according-to-mode',
(if (memq indent-line-function
'(indent-relative indent-relative-maybe))
...
;; The normal case.
(funcall indent-line-function))
the if branch is no longer executed because `indent-line-function' is no
longer `indent-relative' but a closure around it.
You can reproduce the issue with the following recipe:
- Open a new buffer in Fundamental mode (so `indent-line-function' is
`indent-relative')
- Insert : "-- Test"
- From there, <RET> returns to column 0. However, upon evaluating the
following:
M-: (add-function :before-until (local 'indent-line-function) #'ignore)
<RET> now moves point at the same column as the "T" from "Test", in
the new line.
Regards,
--
Nicolas Goaziou 0x80A93738
Nicolas Goaziou <mail@HIDDEN>:monnier@HIDDEN, bug-gnu-emacs@HIDDEN.
Full text available.monnier@HIDDEN, bug-gnu-emacs@HIDDEN:bug#31361; Package emacs.
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