Subject: bug#73404: 30.0.50; [forward/kill/etc]-sexp commands do not behave as expected in tree-sitter modes

From: Mickey Petersen <[email-masked]>
Date: Thu, 26 Sep 2024 10:56:35 +0100

Yuan Fu <[email-masked]> writes:

>> On Sep 20, 2024, at 10:06 PM, Mickey Petersen <[email-masked]> wrote:
>>
>>
>>
>> Examples with javascript-mode. It holds for all modes i tested with a
>> TS equivalent. Let -!- be the starting point and ^N be the subsequent
>> position after a movement command.
>>
>> -!-export const add = (a, b) => a + b;
>>
>> Repeated `C-M-f' yields
>>
>> export const add = (a, b) => a + b;
>>
>>      ^1    ^2  ^3       ^4   ^5  ^6
>>
>>
>> In other words, it works as it always has.
>>
>> Meanwhile, in `js-ts-mode':
>>
>> export const add = (a, b) => a + b;
>>                ^1       ^2   ^3  ^4
>>
>> From ^1 and back with `C-M-b'
>>
>> export const add-!- = (a, b) => a + b;
>>
>> export const add = (a, b) => a + b;
>>             ^1
>>
>> At this point, `C-M-b' no longer goes back. It is stuck.
>>
>>
>> Another example:
>>
>> -!-console.log("Addition result:", result1);
>>
>> With `C-M-f':
>>
>> console.log("Addition result:", result1);
>>
>>       ^1                               ^2
>>
>>
>> This affects every single -sexp function that uses either
>> `forward-sexp-function' or `transpose-sexp-function' to do its job.
>>
>> Thanks.
>>
>
> I’m aware of this problem and it’s quite inconvenient at times, but right now I don’t have a good solution for it. Ideas are welcome.
>
> Basically tree-sitter’s sexp movement works on subtrees. It determines
> the position of the point in the whole parse tree and goes
> forward/back across the next subtree in the parse tree. If there’s no
> more sibling subtrees in the same level to move over, sexp movement
> stops like in lisp. The parse tree is invisible and often groups token
> in unexpected ways, so many times the sexp movement isn’t intuitive.
>

Hi Yuan,

In my opinion, that's not what `sexp' movement is.

Sexp movement is movement by balanced expressions -- and a fallback to
word-like behaviour absent that -- and this is not that. It would be
better to relegate this sort of thing to its own set of keybindings.

> We might need to add a user option so people can easily turn off
> tree-sitter sexp movement, since it isn’t a strict upgrade from the
> generic sexp movement—it’s more of a different flavored sexp movement.

It should be opt-in, not opt-out.

> Yuan