Subject: Re: bug#61655: [Tree sitter] [Feature Request] font-lock function calls, definitions, separately

From: Jacob Faibussowitsch <[email-masked]>
Date: Tue, 21 Feb 2023 10:31:17 -0500

> but it's a relatively small change,

Indeed, after playing around with the syntax queries a bit more, all that is needed to implement this change is the following patch.

Note for the new faces that I populated the `:foreground` fields to match the colors for the example I showed in my first email, but maybe a better default is to leave these faces totally blank and just purely `:inherit` from `font-lock-function-name-face`.

diff --git a/lisp/font-lock.el b/lisp/font-lock.el
index 9e944fe188a..d170123c2ca 100644
--- a/lisp/font-lock.el
+++ b/lisp/font-lock.el
@@ -2026,6 +2026,16 @@ font-lock-function-name-face
   "Font Lock mode face used to highlight function names."
   :group 'font-lock-faces)
 
+(defface font-lock-function-call-face
+  '((t :inherit font-lock-function-name-face :foreground "royalblue1"))
+  "Font Lock mode face used to highlight function calls."
+  :group 'font-lock-faces)
+
+(defface font-lock-member-function-call-face
+  '((t :inherit font-lock-function-name-face :foreground "brightred"))
+  "Font Lock mode face used to highlight member function calls."
+  :group 'font-lock-faces)
+
 (defface font-lock-variable-name-face
   '((((class grayscale) (background light))
      :foreground "Gray90" :weight bold :slant italic)
diff --git a/lisp/progmodes/c-ts-mode.el b/lisp/progmodes/c-ts-mode.el
index b7a487687a8..51a65aa6545 100644
--- a/lisp/progmodes/c-ts-mode.el
+++ b/lisp/progmodes/c-ts-mode.el
@@ -529,8 +529,8 @@ c-ts-mode--font-lock-settings
    :feature 'function
    '((call_expression
       function:
-      [(identifier) @font-lock-function-name-face
-       (field_expression field: (field_identifier) @font-lock-function-name-face)]))
+      [(identifier) @font-lock-function-call-face
+       (field_expression field: (field_identifier) @font-lock-member-function-call-face)]))
 
    :language mode
    :feature 'variable

Best regards,

Jacob Faibussowitsch
(Jacob Fai - booss - oh - vitch)

> On Feb 21, 2023, at 04:55, Dmitry Gutov <[email-masked]> wrote:
> 
> On 21/02/2023 10:28, Yuan Fu wrote:
>> Hmmm, yeah. The builtin tree-sitter maps syntax queries directly into
>> faces, where the third-party tree-sitter maps syntax queries to some
>> syntax types, then maps types to faces. So it would be a bit harder to
>> do fine-grained control like in the builtin tree-sitter, comparing to
>> the third-party one.
>> I’ve thought of this idea before but didn’t pursue it further: Right now
>> we allow capture names to be face names and functions, eg
>> (commment) @font-lock-comment-face
>> or
>> (comment) @xxx-moode-fortify-comment
>> Maybe we can add a third type, arbitrary symbols, like
>> (comment) @comment
>> and add a variables treesit-font-lock-mapping which maps symbols to
>> faces or functions:
>> ((comment . font-lock-comment-face))
>> or
>> ((comment . xxx-mode-fontify-comment))
>> Then we can easily support differentiating between function call and
>> function definition.
> 
> Before we do any of that, don't we need actual different faces to use for e.g. function definitions and function calls?
> 
> Same for variables.
> 
> And if we have those, we might not need the indirection, at least not right away.
> 
> I figured we'd add them in Emacs 30, but it's a relatively small change, if people are interested.