Subject: 29.0.60; typescript-ts-mode does not correctly highlight function-valued variables. [PATCH]

From: Jostein Kjønigsen <[email-masked]>
Date: Wed, 25 Jan 2023 10:41:23 +0100

When working with codebases where people define functions by assigned 
arrow-expressions to local variables, typescript-ts-mode (and 
tsx-ts-mode) currently does not highlight them as function declarations.

// this works
function demoFunction() {
}

// this doesnt
const demoFunction = () => {
};

We actually have a selector for this, but it is not getting triggered, 
because of what looks like ordering issues.

We also have override :t for almost every single feature in this mode, 
making it hard to know how selectors gets applied.

Attached is a patch whic:

1. reorders selectors to correctly highlight function-declaration 
(required change, but not sufficient)
2. disables override everywhere, except for declaration, in order to 
keep fontification correct.

So far I haven't been able to observe any ill side-effects from this 
change, but it might be worth double-checking.

--
Jostein

In GNU Emacs 29.0.60 (build 1, x86_64-pc-linux-gnu, GTK+ Version
  3.24.36, cairo version 1.17.6) of 2023-01-15 built on thinkpad-t14s
Repository revision: 59c3c53efa43e82f0f2e48a4c27d5bd623201d4a
Repository branch: emacs-29
Windowing system distributor 'The X.Org Foundation', version 11.0.12201007
System Description: Arch Linux

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-- 
Vennlig hilsen
*Jostein Kjønigsen*

[email-masked] 🍵 [email-masked]
https://jostein.kjønigsen.no <https://jostein.kjønigsen.no>

From e5de720c5635eeae4b1a3728d94eb4bdb60174d0 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jostein=20Kj=C3=B8nigsen?= <[email-masked]>
Date: Wed, 25 Jan 2023 10:38:09 +0100
Subject: [PATCH] typescript-ts-mode: fix fontification of function-valued
 variables

- remove overrides all over the place... since that means we cant
  override the one place we actually need to!
---
 lisp/progmodes/typescript-ts-mode.el | 20 +++++---------------
 1 file changed, 5 insertions(+), 15 deletions(-)

diff --git a/lisp/progmodes/typescript-ts-mode.el b/lisp/progmodes/typescript-ts-mode.el
index 34030968806..25cc327d05f 100644
--- a/lisp/progmodes/typescript-ts-mode.el
+++ b/lisp/progmodes/typescript-ts-mode.el
@@ -132,26 +132,21 @@ typescript-ts-mode--font-lock-settings
 Argument LANGUAGE is either `typescript' or `tsx'."
   (treesit-font-lock-rules
    :language language
-   :override t
    :feature 'comment
    `((comment) @font-lock-comment-face)
 
    :language language
-   :override t
    :feature 'constant
    `(((identifier) @font-lock-constant-face
       (:match "^[A-Z_][A-Z_\\d]*$" @font-lock-constant-face))
-
      [(true) (false) (null)] @font-lock-constant-face)
 
    :language language
-   :override t
    :feature 'keyword
    `([,@typescript-ts-mode--keywords] @font-lock-keyword-face
      [(this) (super)] @font-lock-keyword-face)
 
    :language language
-   :override t
    :feature 'string
    `((regex pattern: (regex_pattern)) @font-lock-regexp-face
      (string) @font-lock-string-face
@@ -159,7 +154,7 @@ typescript-ts-mode--font-lock-settings
      (template_substitution ["${" "}"] @font-lock-misc-punctuation-face))
 
    :language language
-   :override t
+   :override t ;; for functions assigned to variables
    :feature 'declaration
    `((function
       name: (identifier) @font-lock-function-name-face)
@@ -174,6 +169,10 @@ typescript-ts-mode--font-lock-settings
      (required_parameter (identifier) @font-lock-variable-name-face)
      (optional_parameter (identifier) @font-lock-variable-name-face)
 
+     (variable_declarator
+      name: (identifier) @font-lock-function-name-face
+      value: [(function) (arrow_function)])
+
      (variable_declarator
       name: (identifier) @font-lock-variable-name-face)
 
@@ -188,10 +187,6 @@ typescript-ts-mode--font-lock-settings
      (arrow_function
       parameter: (identifier) @font-lock-variable-name-face)
 
-     (variable_declarator
-      name: (identifier) @font-lock-function-name-face
-      value: [(function) (arrow_function)])
-
      (variable_declarator
       name: (array_pattern
              (identifier)
@@ -205,7 +200,6 @@ typescript-ts-mode--font-lock-settings
      (import_clause (named_imports (import_specifier (identifier)) @font-lock-variable-name-face)))
 
    :language language
-   :override t
    :feature 'identifier
    `((nested_type_identifier
       module: (identifier) @font-lock-type-face)
@@ -234,7 +228,6 @@ typescript-ts-mode--font-lock-settings
        (_ (_ (_ (identifier) @font-lock-variable-name-face)))]))
 
    :language language
-   :override t
    :feature 'property
    `((property_signature
       name: (property_identifier) @font-lock-property-face)
@@ -249,7 +242,6 @@ typescript-ts-mode--font-lock-settings
       @font-lock-property-face))
 
    :language language
-   :override t
    :feature 'expression
    '((assignment_expression
       left: [(identifier) @font-lock-function-name-face
@@ -266,7 +258,6 @@ typescript-ts-mode--font-lock-settings
         property: (property_identifier) @font-lock-function-name-face)]))
 
    :language language
-   :override t
    :feature 'pattern
    `((pair_pattern
       key: (property_identifier) @font-lock-property-face)
@@ -274,7 +265,6 @@ typescript-ts-mode--font-lock-settings
      (array_pattern (identifier) @font-lock-variable-name-face))
 
    :language language
-   :override t
    :feature 'jsx
    `((jsx_opening_element
       [(nested_identifier (identifier)) (identifier)]
-- 
2.39.1