bug#67207: [PATCH] Add elixir-ts-mode-hook to elixir-ts-mode

[Stefan Monnier via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

> Stefan, does this mean define-derived-mode has some deficiency?
> Many/most modes defined using it don't have an explicit hook
> definition, so should we now define a mode hook for all of them?

Usually we don't have good ideas of `:options` to provide for hook
variables, so it's not very useful to expose them to Custom.

Also, it's not rare for hook variables to be modified by other packages,
which again votes in favor of not exposing them to Custom.

But some mode maintainers do like to expose them to Custom for their
users' convenience.  Usually I look at it as a hint that there's
something missing elsewhere (for the patch at hand, maybe some kind of
`global-eglot-mode` would be a better answer in the longer term).

We could try and extend `define-derived-mode` to allow it to expose the
hook to Custom, with `:options` and whatnot, but it doesn't seem worth
the trouble since the maintainer can use a separate explicit `defcustom`
instead, as the OP's patch does.


        Stefan