Subject: treesit-major-mode-setup should not call font-lock-mode

From: Dmitry Gutov <[email-masked]>
Date: Wed, 27 Sep 2023 03:17:57 +0300

X-Debbugs-CC: Yuan Fu <[email-masked]>

It doesn't seem necessary (everything seems to work okay without that 
call), and it's not the right thing idiomatically (the user should have 
the ability to disable global-font-lock-mode).

If it does get called, the call to treesit-font-lock-recompute-features 
should happen before that.

The report was triggered by somewhat unusual circumstances (somebody 
trying out mmm-mode together with typescript-ts-mode: 
https://github.com/dgutov/mmm-mode/issues/138), but the fix seems easy 
and natural enough.

To reproduce the bug, though, try this:

(with-current-buffer (generate-new-buffer "foo")
   (let (font-lock-support-mode)
     (typescript-ts-mode)))

It results in

Debugger entered--Lisp error: (treesit-query-error "Node type error at" 
2 "(jsx_opening_element [(nested_identifier (identifier)) (identifier)] 
@typescript-ts-jsx-tag-face) (jsx_closing_element [(nested_identifier 
(identifier)) (identifier)] @typescript-ts-jsx-tag-face) 
(jsx_self_closing_element [(nested_identifier (identifier)) 
(identifier)] @typescript-ts-jsx-tag-face) (jsx_attribute 
(property_identifier) @typescript-ts-jsx-attribute-face)" "Debug the 
query with `treesit-query-validate'")
   treesit-query-capture(#<treesit-node program in 1-1> 
#<treesit-compiled-query> 1 1)
   (let* ((delta-start ...
   treesit--font-lock-fontify-region-1(#<treesit-node program in 1-1> 
#<treesit-compiled-query> 1 1 nil nil)
   (let ((sub-node (car tail)))...
   treesit-font-lock-fontify-region(1 1 nil)
   font-lock-fontify-syntactically-region(1 1 nil)
   font-lock-default-fontify-region(1 1 nil)
   font-lock-fontify-region(1 1 nil)
   font-lock-default-fontify-buffer()
   font-lock-fontify-buffer()
   font-lock-initial-fontify()
   font-lock-mode(1)
   (progn (set (make-lo...
   treesit-major-mode-setup()
   typescript-ts-mode()

because typescript-ts-mode's treesit-font-lock-settings hide the jsx 
rule (which the typescript grammar itself doesn't support, only the tsx 
one does) using the absence of that feature in 
treesit-font-lock-feature-list. But for that to take effect, the call to 
'treesit-font-lock-recompute-features' needs to happen first. The 
jit-lock conceals the problem by inhibiting the first fontification 
until the major mode function has run and the buffer is visible. I ended 
up disabling it in mmm-mode's auxiliary temp buffer because it spams the 
message "Not enabling jit-lock: it does not work in indirect buffer".