Kévin Le Gouguec <kevin.legouguec@gmail.com> writes:

> Questions before proceeding to ChangeLog entries & regression tests:

For better or worse, I ended up proceeding to both these things, and
then some.  Let me know if the attached patches make sense; tested with

  make -j8 bootstrap && make -C test files-tests


Tentative answers to my questions:

> 1. Is this something we would like Emacs to recognize out of the box, or
> is it too niche?

Assuming yes.

> 2. What about the more general forms shown in (info "(coreutils) env
> invocation")?
>
>   #!/usr/bin/env -[v]S[OPTION]... [NAME=VALUE]... COMMAND [ARGS]...

Didn't go as far as handling -v nor NAME=VALUE pairs, but that could be
added later if we ever feel like it.

> 3. Assuming we do want to amend that regexp, would it be possible to use
> rx here?  OT1H guessing "no" because files.el is pre-reloaded, whereas
> rx.el is not; OTOH I see that files.el requires easy-mmode at
> compile-time, and that package does not show up in loadup.el, so…
> settling for "maybe?"

Figured rx was similar to pcase in that regard:

* They need to be required explicitly despite their macros being
  "autoloaded", because files.el is loaded during bootstrap before
  autoloading is set up.

* Somehow that does not cause them to be preloaded?  At least going by
  emacs -Q,
  * featurep returns nil,
  * preloaded-file-list does not include them.