bug#67246: 30.0.50; elixir-ts-mode uses faces inconsistently

[Dmitry Gutov <dmitry@gutov.dev>]

On 25/11/2023 10:33, Andrey Listopadov wrote:

>> And here's another aspect: the default built-in theme doesn't
>> distinguish many of the faces (and the same is true for many other
>> built-in themes). E.g. it doesn't distinguish variable-name-face from
>> variable-use-face or function-name-face from function-call-face.
> 
> I'm wondering if font-lock.el needs a bit more generic faces, as
> packages often define their own faces, that aren't supported by themes
> in any way.  Again, the example with elixir-mode isn't to bash the
> developers, but before 2019 elixir-mode (not elixir-ts-mode) defined a
> few faces with explicit colors.  Here's a commit that fixed that
> https://github.com/elixir-editors/emacs-elixir/commit/f101c676cc9485aa22ec088a71d8afc72cda3d58
> but before it, `elixir-atom-face' and `elixir-attribute-face' were
> `RoyalBlue4' and `MediumPurple4' no matter what theme you were using.
> IIRC the CIDER package also defines some faces like that, so it's
> somewhat common.

As long as the faces are for unusual contexts and have some fallbacks 
(or preferably inherit from some of the core ones), that's fair practice.

> I can't come up with missing faces, and most modes I use define extra
> faces in terms of inheritance to the inbuilt faces,

Right.

> but maybe
> font-lock-symbol-face is worth including, as some languages may want to
> distinguish these like elixir does right now with `elixir-ts-atom-face'.

I agree we could add more. E.g. a face like that could automatically be 
used for "keywords" in Elisp (and Clojure, and other Lisps) and 
"symbols" in Elixir in Ruby.

What makes me pause is naming: the terminology is a mess here across 
languages. "symbols" usually mean something else in Emacs (and in Lisp 
languages in general), whereas "keywords" mean something else across 
most other languages. Using the name font-lock-symbol-face is bound to 
cause confusion at least across Lisp programmers. Luckily, 
'font-lock-keyword-face' is already taken, so we don't have to consider 
this alternative (which would puzzle the rest of the programming world).

The docstring of 'font-lock-constant-face' says "Face name to use for 
constant and label names", but a name 'font-lock-label-name' sounds 
pretty bland... OTOH, there are labels in C, but nothing with that 
particular name in Elixir, Ruby or Lisp (aside from one macro, I suppose).