GNU bug report logs - #66223
treesit-major-mode-setup should not call font-lock-mode

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From: Dmitry Gutov <dmitry <at> gutov.dev>
To: 66223 <at> debbugs.gnu.org
Cc: yuan fu <casouri <at> gmail.com>
Subject: bug#66223: treesit-major-mode-setup should not call font-lock-mode
Date: Wed, 27 Sep 2023 03:17:57 +0300

X-Debbugs-CC: Yuan Fu <casouri <at> gmail.com>

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".

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