bug#60655: 30.0.50; tree-sitter: `treesit-transpose-sexps' is broken.

[Theodor Thornhill]

Mickey Petersen <mickey@masteringemacs.org> > The tree-sitter-enabled function, 
`treesit-transpose-sexps', that is called by transpose-sexps, is broken.
>
> It uses a naive method of sibling adjacency to determine
> transpositions. But it is unfortunately not correct.
>
> Python:
>
>
>   def -!-foo():
>       pass
>    
> Turns into this with `C-M-t':
>
>   def ()foo:
>       pass
>
> But it ought to be:
>
>   foo def():
>       pass
>
>
> It's swapping two siblings that are indeed adjacent in the tree, but
> not on screen, which is confusing and a regression from its previous
> behaviour.
>

I can try to make transpose-sexps rely on only swapping "allowed"
node-types?  That would be able to keep the new, better function, yet
still disallow these syntax-breaking transposes.  What do you think?

> You could make a cogent argument that both approaches are wrong from a
> syntactic perspective, but I think that misses the broader point that
> `C-M-t' now does something errant and unexpected.

I don't really see how "foo def():" is any better at all.  We gain some
great improvements with this "naive" method - namely:

if 5 + 5 == 10 then 10 else 100 + 100.  If point is on the else the 100
+ 100 wil be swapped by 10, but the old behavior will be broken. 

>
> Worse, it's not possible to revert to the old behaviour (see
> bug#60654)
>
>

Right.

Thanks,
Theo