bug#11037: 24.0.94; gnutls-cli.exe program not found

[Eli Zaretskii <eliz@gnu.org>]

> Date: Thu, 22 Mar 2012 20:45:40 +0000
> From: Uday S Reddy <u.s.reddy@cs.bham.ac.uk>
> Cc: Lars Magne Ingebrigtsen <larsi@gnus.org>,
>     u.s.reddy@cs.bham.ac.uk,
>     11037@debbugs.gnu.org
> 
> I can verify that putting your binary of gnutls on system PATH worked fine
> with Emacs 24.

Great.

> The basic bug report here was that Emacs couldn't find gnutls-cli.exe that
> was available on exec-path.  That was simply based on my misunderstanding of
> where it is supposed to be found.  Since the README.W32 file says that it
> should be found during startup, it implies that it needs to be put on the
> system PATH.
> 
> Perhaps all that you need to do in response to this bug report is to add a
> line in README.W32 to the effect that the binaries should be on system PATH,
> to help out other dimwits like me.

I will add that, but please note that this is in no way specific to
Windows.  There's a subtle difference between exec-path and PATH, in
that exec-path is only used by Emacs's own code to find executables it
runs directly.  By contrast, PATH is used by external programs,
system-level APIs, and the OS features in general.  As an example, a
program invoked through shell-command and its ilk _must_ be on PATH,
because it's the shell that will look for it, not Emacs; Emacs only
looks for the shell itself.  Similarly, to load a dynamic library,
Emacs uses system APIs, which use PATH and not exec-path.

So if what you tried to accomplish needed either shell-command or
loaded a DLL, exec-path will not help.

(To keep your sanity, I suggest to always have exec-path derived from
PATH, and not modify exec-path inside Emacs so that it deviates from
PATH.)