bug#59415: 29.0.50; [feature/tree-sitter] c-ts-mode fails to fontify a portion of a large C file

[Theodor Thornhill via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

>> This diff fixes the font-lock issues:
>> 
>> diff --git a/lisp/treesit.el b/lisp/treesit.el
>> index 674c984dfe..0f84d8b83e 100644
>> --- a/lisp/treesit.el
>> +++ b/lisp/treesit.el
>> @@ -774,12 +774,12 @@ treesit-font-lock-fontify-region
>>       ;; will give you that quote node.  We want to capture the string
>>       ;; and apply string face to it, but querying on the quote node
>>       ;; will not give us the string node.
>> -      (when-let ((root (treesit-buffer-root-node language))
>> +      (when-let (
>>                  ;; Only activate if ENABLE flag is t.
>>                  (activate (eq t enable)))
>>         (ignore activate)
>>         (let ((captures (treesit-query-capture
>> -                         root query start end))
>> +                         (treesit-node-on start end) query start end))
>>               (inhibit-point-motion-hooks t))
>>           (with-silent-modifications
>>             (dolist (capture captures)
>> 
>> 
>> However, the comment right above makes a case for why we should have
>> this.  BUT, is this still relevant, Yuan, after the changes in treesit
>> reporting what has changed etc?  What exact case is that an issue?  And
>> is it more severe than the behavior this bug is exhibiting?
>
> The case described by the comment is still relevant. With this patch,
> the quote described in that case still wouldn’t be fontified. We can
> use some heuristic to get a node “large enough” and not the root
> node. Eg, find some top-level node. That should make query-capture
> much faster.
>

I appreciate the explanation.  I think getting the root is a bit
excessive.  I got the same results as you in the capture.  Maybe reuse
the treesit-defun-type-regexp, and default to root if none found?