Re: Recent updates to tree-sitter branch

[Ihor Radchenko <yantar92@gmail.com>]

Yuan Fu <casouri@gmail.com> writes:

>>> Also bear in mind that the override flag can only be applied to the whole query, rather than individual captured nodes.
>> 
>> How does it change anything? I may be misunderstanding something---can
>> you provide some illustrative example clarifying whole query vs.
>> individual notes?
>
> What I meant is that, for font-lock-keywords, one can set override flag for each individual match:
>
> (string-regex font-lock-string-face t)
> (function-name-regexp font-lock-function-name-face nil)
> (class-name-regexp font-lock-type-face t)
> ...
>
> But for tree-sitter, a query contains many matches and the flag is set for the query. So if I want to use different override flag for different matches, I need to split them into two queries:
>
> (treesit-font-lock-rules
>  :language 'python
>  :override 'append
>  '((string) @python--treesit-fontify-string
>    ((string) @font-lock-doc-face
>     (:match "^\"\"\"" @font-lock-doc-face))
>    (interpolation (identifier) @font-lock-variable-name-face))
>
>  :language 'python
>  :override nil
>  '((function_definition
>     name: (identifier) @font-lock-function-name-face)
>
>    (class_definition
>     name: (identifier) @font-lock-type-face)
>
>    ;; Comment and string.
>    (comment) @font-lock-comment-face))

> That means if we use override=nil as default, it is very likely that users need to explicitly set override to t for the whole query, or split the query into separate parts. Nothing serious, but it seems less convenient.

What about allowing (@python--treesit-fontify-string 'append) to specify
the override?

> A real use-case for override is how I fontified Python strings above. I have three matches for (1) all strings (2) docstrings (3) variable names in string interpolations. IMO it’s intuitive and convenient for later more specific matches to override earlier more general matches.

The current convention in font-lock-keywords is exactly opposite -
earlier matches are more specific, and they are later not replaced by
later more general matches.

Also, for reference, I am currently developing parser-based
fontification for Org.

I am using a somewhat different approach (closer to font-lock-keywords):

((drawer property-drawer) ;; <- match node types
  (:begin-marker 'org-drawer t) ;; <- apply fontification to :begin-marker field inside 
  (:end-marker 'org-drawer t)) ;;  <- ...                    :end-marker ....
((headline inlinetask)
  (:title-line
   (if (org-element-match-property :archivedp) ;; <- Elisp matching of the node properties
       'org-archived
     (pcase (org-element-match-property :todo-type) ;; <- ....
       (`todo (when org-fontify-todo-headline 'org-headline-todo))
       (`done (when org-fontify-done-headline 'org-headline-done))
       (_ nil)))
   t)) ;; <- override
 ((bold italic underline verbatim code strike-through)
   (:full-no-blank '(face nil org-emphasis t))) ;; <- fontify contents of the matched node
   
Also, see https://github.com/yantar92/org/blob/feature/org-font-lock-element/lisp/org-font-lock.el#L574

From my experience re-implementing the vanilla fontification,
fontification order is important and may create subtle issues when not
designed carefully.

-- 
Ihor Radchenko // yantar92,
Org mode contributor,
Learn more about Org mode at <https://orgmode.org/>.
Support Org development at <https://liberapay.com/org-mode>,
or support my work at <https://liberapay.com/yantar92>