bug#14541: 24.3.50; `ediff-buffers' does not play well with recent Cygwin version

[Drew Adams <drew.adams@oracle.com>]

> As I've been unsuccessfully trying to explain to you, there can be no
> such setup file.

And yet there is such a file.

> > But especially, please do provide something better.  I will be
> > the first to use it and to point others to it, believe me!
> 
> I think I've already said that if you want to set that option and be
> sure it takes effect, you need to do it from the system panel.

I think I've already said that I recognize that.

> That's what you might put in a comment in setup-cygwin.el, 

Which is just what I did.  Here is the comment, in case you have
not already taken a look:

;;; Without this env var setting, Cygwin causes `ediff-buffers', at
;;; least, to raise an error.  Making this setting here might have no
;;; effect, as the env var is checked only by the first Cygwin process
;;; invoked during your Windows session.  For best results, set this
;;; env var globally, in Windows itself.  An alternative might be to
;;; use `cygpath' to change from MS Windows file names to POSIX.

I might even cite this bug report there, so users can get more detail.

> without trying to produce unknown and potentially undefined or
> unwanted effects by setting the CYGWIN environment variable.

Sorry, bug I want to set that variable.  In the file, just in case
it is not set yet.

> >> It must already be set before Emacs gets started.
> >
> > Not as far as I can see.  Not for the case I use it for: using
> > Cygwin almost exclusively with Emacs.  In that use case, the
> > first Cygwin process is launched by Emacs.
> 
> There never was a dispute that it didn't solved your problem.  In
> general however, you can't even be sure that Emacs starts the first
> Cygwin process after it gets to setup-cygwin.el and if you install
> Cygwin to provide services there will never be any point in time where
> there is no Cygwin process while your session is active.

Maybe so.  There was never any dispute that setting the var in this
file is not a panacea.

> > But wasn't it you, BTW, who said that an alternative (presumably
> > working reliably) is to "use cygpath to convert to POSIX instead"?
> 
> Yes.  That warning says "please do not hand a Windows path to Cygwin",
> so you would never see this warning or need an option to suppress it if
> you would use POSIX paths only.  The tool to convert between the two
> representations is cygpath.

You claimed explicitly that the _only_ solution is to set the env var
at the system level.  And yet you also claim that there is another
solution: convert to POSIX using cygpath.