bug#59498: 29.0.50; c++-ts-mode get wrong-type-argument error when enabled

[Stefan Monnier]

>> I added treesit-comment-start/end to help indenting comments. So this is
>> the correct way to use them. The following comment explains why I created
>> new variables:
>> 
>> ;; `comment-start' and `comment-end' assume there is only one type of
>> ;; comment, and that the comment spans only one line.  So they are not
>> ;; sufficient for our purpose.
>
> ??? This is surprisingly unclean, IMO.  For starters, the names of the
> variables are confusing.  The need to define two sets of comment-start and
> comment-end regexps is also a nuisance and a source of errors.
>
> How do non-treesit modes handle this issue?  Why do the treesit-based modes
> need something special here?
>
> Stefan, any ideas?

`comment-start` and `comment-end` do not describe the set of possible
comment delimiters.  They describe the comment delimiters that should be
*inserted* when we do things like `comment-dwim`.

To find/match comment delimiters we have `comment-start-skip` and
`comment-end-skip`.  They're not ideal, but they've been good enough so far.
They don't say which comment starter matches which comment-ender (that
was done by the syntax-tables), but tree-sitter should be able to tell
us that when we need it.

It would be nice if we could avoid the need to set/use
`comment-start-skip` and `comment-end-skip` when using tree-sitter.
Maybe we can compute their values from the tree-sitter grammar.
But getting rid of uses of those vars will take a fair bit more work,
I think.


        Stefan