bug#60128: 30.0.50; [PATCH]: Add treesit-transpose-sexps

[Yuan Fu]

> On Dec 26, 2022, at 12:53 PM, Theodor Thornhill <theo@thornhill.no> wrote:
> 
> Theodor Thornhill <theo@thornhill.no> writes:
> 
>> Theodor Thornhill <theo@thornhill.no> writes:
>> 
>>> Hi there!
>>> 
>>> Attached is a patch that enables transpose-sexps for tree-sitter enabled
>>> modes.
>>> 
>>> This function will swap the node _before_ node-at-point with the node
>>> _after_, so it would do something like:
>>> 
>>>       foo a|nd bar => bar and foo|
>>> 
>>> or
>>>       foo(a + 4,| y + c * b, b, d); => foo(y + c * b, a + 4|, b, d);
>>> 
>>> It will _not_ try to swap things that are not siblings.  I think that
>>> makes sense in the case of non-lisp languages, since _most_ places you
>>> can transpose-sexps you will end up with broken code.
>>> 
>> 
>> from 'transpose-subr-1':
>> 
>>  (if (> (cdr pos1) (car pos2)) (error "Don't have two things to
>>  transpose"))
>> 
>> I added this hack into the function in the patch, but I think that
>> triggering an error is too much.
>> 
>>    ;; Hack to trigger the error message in `transpose-subr-1' when we
>>    ;; don't have siblings to swap.
>>    (list (cons 0 1) (cons 0 1))))
>> 
>> I guess I could just follow suit in my function and do like in the
>> following patch:
>> 
>> Theo
> 
> 
> Considering there is both a bug-report _and_ a discussion around this I
> guess the best idea is to add the patch to this bug report, and continue
> discussing this in the report rather than emacs-devel?
> 
> What do you think about this patch?
> 
> (copied from emacs-devel):
> It feels a little iffy how to handle the separate return values, but it
> works.  I'd be super happy for some feedback on how to best solve that,
> though :)

By separate return values, do you mean the function returns a cons of cons? It 
seems fine to me. Though I think the docstring could be more specific. Like 
saying return a cons (REGION . REGION), where REGION is (BEG . END), where BEG 
and END...

> 
> Also, I made the treesit-transpose-sexps a little better imo, in that we
> only find named nodes to swap, but use every available node for the
> entry. We rarely, if ever want to swap the unnamed nodes.
> 
> Eli, does this require a NEWS entry or more documentation?

IMHO a backend/helper function shouldn’t signal a user-error, it’s better to 
return nil and let the command to signal errors.

Yuan