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Subject: |
29.0.92; Tree-Sitter/which-function Narrow/Widen causes modified buffer |
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Date: |
Tue, 27 Jun 2023 22:23:52 -0400 |
This problem seems to manifest with multiple tree-sitter modes. It
appears there is an interaction with which-function-mode and tree-sitter
which causes the buffer to be considered modified either after a narrow
or widen of the buffer.
To reproduce this, use a "hello_world.c" as follows:
--8<---------------cut here---------------start------------->8---
#include <stdio.h>
int main (void)
{
printf("Hello, world!\n");
return 0;
}
--8<---------------cut here---------------end--------------->8---
Running "emacs -Q" with the corresponding tree-sitter grammar library
installed. Move into the main function and narrow-to-defun. In some
modes, I've seen this cause the buffer to show as modified, however with
this example, it seems to occur after widening.
The following sequence of commands can be used to reproduce the issue:
C-x C-f ~/hello_world.c
M-x c-ts-mode
M-x which-function-mode
C-x n d
C-x n w
At this point, the modeline shows that the buffer is modified, and
running "M-: (buffer-modified-p)" indicates "t". As previously
mentioned, this appears to only happen with tree-sitter modes when
which-function-mode is enabled in the buffer.
I then repeated the same but also triggered a backtrace on the first
change as follows:
M-: (add-to-list 'first-change-hook #'backtrace)
With that in place, the following is the generated traceback:
backtrace()
treesit--font-lock-notifier(((1 . 21)) #<treesit-parser for c>)
treesit-buffer-root-node(c)
treesit-node-at(68)
treesit--things-around(68
"\\(?:class_specifier\\|enum_specifier\\|function_defi..."
c-ts-mode--defun-valid-p)
treesit-thing-at-point(("\\(?:class_specifier\\|enum_specifier\\|function_defi..."
. c-ts-mode--defun-valid-p) top-level)
treesit-defun-at-point()
treesit-add-log-current-defun()
c-ts-mode--emacs-current-defun-name()
add-log-current-defun()
which-function()
which-func-update-1(#<window 3 on hello_world.c>)
which-func-update()
apply(which-func-update nil)
timer-event-handler([t 0 0 500000 t which-func-update nil idle 0 nil])
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--- Begin Message ---
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Subject: |
Re: bug#64321: 29.0.92; Tree-Sitter/which-function Narrow/Widen causes modified buffer |
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Date: |
Wed, 28 Jun 2023 13:09:41 -0700 |
> On Jun 28, 2023, at 9:25 AM, Troy Brown <brownts@troybrown.dev> wrote:
>
> On Wed, Jun 28, 2023 at 12:04 AM Yuan Fu <casouri@gmail.com> wrote:
>>
>> Narrowing and widening are transparent to tree-sitter, so when the buffer
>> widens, from tree-sitter’s POV, text are added to the buffer. Which-func
>> calling the tree-sitter current-defund function ultimately leads to
>> tree-sitter calling treesit—font-lock-notifier which puts text properties on
>> the “added” portion of the buffer, which changed the modified status.
>>
>> treesit—font-lock-notifier should put text properties without changing
>> modified status, like what jit-lock does. This patch should fix it.
>>
>
> Thanks for the explanation and the supplied patch. I can confirm that
> this patch fixes the issue.
Cool, thanks, pushed.
Yuan
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