bug#62412: 29.0.60; strange c++ indentation behavior with tree sitter

[João Távora]

On Sat, Mar 25, 2023 at 10:19 AM Theodor Thornhill <theo@thornhill.no> wrote:
>
>
>
> On 25 March 2023 09:53:31 CET, "João Távora" <joaotavora@gmail.com> wrote:
> >On Fri, Mar 24, 2023 at 10:02 PM Theodor Thornhill via Bug reports for
> >GNU Emacs, the Swiss army knife of text editors
> ><bug-gnu-emacs@gnu.org> wrote:
> >e about the original purpose for this rule, CC’ing Theo.
> >> >
> >> >Yuan
> >> I'll look more deeply into the cause of this, but the rule is covering 
> >> some preproc directives iirc.
> >>
> >> Unfortunately tree-sitter behaves better when auto pairs is used. I would 
> >> advise people to use electric-pairs-mode (if that's the correct name, on 
> >> mobile now) to avoid these sorts of issues.
> >
> >electric-pair-mode, it's not on by default.
> >
> >But, for some reason, electric-indent-mode _is_ on by default,
> >at least in c++-ts-mode.
> >
> >So this has nothing to do with tree-sitter IMO, it's just
> >electric-pair-mode doing its thing.
> >
> >Why is it on by default?  A fair number of users don't like
> >this electricity, or prefer to have it toned down.  At least
> >this has been the  argument for not turning on electric-pair-mode
> >by default, which is a much less jarring mode IMO, and one which
> >would solve these problems.
> >
> >João
>
> Yeah, maybe! But I was under the impression that indentation was electric by 
> default in most modes, but I may be mistaken.
>
> The reason I mentioned electric-pair-mode is that the parser fails less often 
> when the closing paren or bracket is inserted, as it is much simpler to have 
> a functional ast.

Sure.  I wrote electric-pair-mode and that's exactly the point.

electric-indent-mode is on by default, but many modes just
use the default value for electric-indent-chars, which only
contains a newline, and so they aren't affected by this problem.

In c++-ts-mode, you gave electric-indent-chars a richer value,
including characters such as '}', ':' and ';'.  This is not
unreasonable, but, as you've discovered, only really goes together
well with electric-pair-mode.

João