GNU bug report logs - #79363
31.0.50; Font locking issue in go-ts-mode when tree-sitter grammar is automatically installed

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Message #14 received at 79363 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Roi Martin <jroi.martin <at> gmail.com>, Randy Taylor <dev <at> rjt.dev>
Cc: Yuan Fu <casouri <at> gmail.com>, 79363 <at> debbugs.gnu.org
Subject: Re: bug#79363: 31.0.50;
 Font locking issue in go-ts-mode when tree-sitter grammar is
 automatically installed
Date: Tue, 02 Sep 2025 14:24:30 +0300

> From: Roi Martin <jroi.martin <at> gmail.com>
> Date: Mon, 01 Sep 2025 23:31:52 +0200
> 
> Steps to reproduce:
> 
> 1. Run
>      emacs -Q --init-directory=/tmp/go-ts-mode-bug
> 2. Eval
>      (setopt treesit-enabled-modes '(go-ts-mode))
> 3. Open .go file
> 4. Answer y to the question
>      Tree-sitter grammar for `go' is missing; install it?  (y or n)
> 5. go-ts-mode emits the following warning and definitions are not
>    highlighted correctly.
> 
>      ⛔ Warning (treesit-font-lock-rules-mismatch): Emacs cannot compile
>      every font-lock rules because a mismatch between the grammar and the
>      rules.  This is most likely due to a mismatch between the font-lock
>      rules defined by the major mode and the tree-sitter grammar.
>      
>      This error can be fixed by either downgrading the grammar
>      (tree-sitter-go) on your system, or upgrading the major mode package.
>      The following are the temporarily disabled features:
>      
>      - `definition' for go.
> 
> In GNU Emacs 31.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version
>  3.24.49, cairo version 1.18.2)
> Repository revision: 3c94ae5a37eac0191fe5d8bd85164b190ac10244
> Repository branch: master
> 
> I took a quick look and I think this is caused by the following issue:
> 
> 1. `go-ts-mode--font-lock-settings' depends on the following functions:
> 
>      (defun go-ts-mode--iota-query-supported-p ()
>        "Return t if the iota query is supported by the tree-sitter-go grammar."
>        (ignore-errors
>          (or (treesit-query-string "" '((iota) @font-lock-constant-face) 'go) t)))
>      
>      (defun go-ts-mode--method-elem-supported-p ()
>        "Return t if Go grammar uses `method_elem' instead of `method_spec'."
>        (ignore-errors
>          (or (treesit-query-string "" '((method_elem) @cap) 'go) t)))
> 
> 2. In this sceneario we don't have the Go grammar installed yet.  So,
>    `treesit-query-string' returns a `not-found' error.
> 3. Because of the previous error, `go-ts-mode--method-elem-supported-p'
>    returns `nil'.  Thus, the "definition" rule uses "method_spec" which
>    is not supported by the default grammar (commit
>    "12fe553fdaaa7449f764bc876fd777704d4fb752").
> 
>      (defvar go-ts-mode--font-lock-settings
>        (treesit-font-lock-rules
>         ...
>         :language 'go
>         :feature 'definition
>         `(...
>           (,(if (go-ts-mode--method-elem-supported-p)
>                 'method_elem
>               'method_spec)
>            name: (field_identifier) @font-lock-function-name-face)
> 
> Please, take this analysis with a pinch of salt.  I'm not familiar with
> the code base.  But I hope it makes sense.

Thanks.

Randy and Yuan, could you please take a look?

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