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

[Andrey Listopadov <andreyorst@gmail.com>]

Dmitry Gutov <dmitry@gutov.dev> writes:

> The idea was to balance the new look between the "old" major modes and
> the newer, shinier ones. So that the overall style still somewhat
> appeals to the existing audience, just with added features and more
> precision. Here's a Reddit recent thread about the same sentiment:
> https://www.reddit.com/r/emacs/comments/18152qo/overcolorization_everything_is_purple/
> It discusses a post written by Andrey, BTW.

Yes, I published this post after submitting the bug in order to raise
awareness among the community.

> One could basically say that a function call and a properly lookup are
> easy to distinguish from glancing at the text, there's not much need
> to highlight them. As opposed to e.g. implicit variable declaration or
> function declaration.

Yeah, as I said in my post, highlighting important parts of the code,
like macro calls, or dynamic/global variables tells you that you're
looking at something more intricate, that is otherwise syntactically
indistinguishable from regular code.

> 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.

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