bug#70198: M-x shell: deal with environment variables present when tab expanding

[Eli Zaretskii <eliz@gnu.org>]

> From: Federico Tedin <federicotedin@gmx.de>
> Cc: jidanni@jidanni.org,  70198@debbugs.gnu.org
> Date: Wed, 10 Jul 2024 20:11:07 +0200
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > What happens if the '=' character is quoted?
> 
> What would be an example of this? (in the context of writing shell
> commands).

Something like

  $ FOO='foo=bar' date

> > I think a better idea might be first to try to find what is "the word
> > at point", and then complete only that word.  WDYT?
> 
> Yep, however I do think we still need to walk back some words in order
> to ensure that we are not autocompleting an argument; for example
> 
> $ echo whoam[TAB]
> 
> should not autocomplete to "whoami", I'm assuming.

It should, just not command completion.

> So for the actual walking backwards we need to maybe:
> - modify shell-backward-command so that it leaves the point at the
> beginning of the command, but after any env vars
> - or, move backwards using `shell-command-regexp' until the last thing
> that does not look like FOO=BAR or FOO= is found.
> 
> All of this just to ensure that the word at point is an actual command
> and not an argument to a command. Maybe this approach itself could be
> re-evaluated though !

If we want to detect FOO=BAR, we need to use syntax classes, and I'm
not sure regexps are the best instrument for that.