very strange error from git under emacs

[Stephen Leake <stephen_leake@stephe-leake.org>]

I'm running git under Emacs, via the DVC package.

I'm getting a very strange error, but only for one git command (at least
so far):

from 'git stash save':

fatal: Unable to create '/Projects/emacs/master/c:/Projects/emacs/master/.git/index.stash.1888.lock': No such file or directory
Cannot save the untracked files

Apparently the c: is confusing git. I can't figure out where it is
comming from.

I'm running on Cygwin git under Windows 8; this problem did not appear
on Windows 7 (with an older Cygwin). It happens with Emacs master and
Emacs 24.3.

The command works fine in a Cygwin bash shell.

In Emacs master I'm using 'make-process' to spawn git directly,
capturing stdout in a buffer, and stderr in a separate buffer via a
pipe-process.

In Emacs 24.3 I'm using `call-process' to spawn Cygwin sh, which then
runs git, using shell pipe redirection to capture stderr in a file.

Has anyone seen anything like this?

I can't figure out what is different between the Cygwin bash environment
when running that in a comint buffer under Emacs, and the Cygwin sh
environment in Emacs 24.3, or the direct spawn of git in Emacs 25.

Running 'git stash save' from a Windows cmd.exe shell, with Cygwin bin
in path, works fine. I first tried that without Cygwin git in path;
apparently git spawns a shell to do stuff for this command.

I'll also ask on the git mailing list; maybe they can explain why 'stash
save' works differently from other git commands, or how it builds that
filename.

-- 
-- Stephe