Oleg, I tried reusing your package snippet from
http://lists.gnu.org/archive/html/help-guix/2017-09/msg00074.html
by setting

               (url "git://localhost/~ambrevar/projects/emacs")

but it fails for me:

	> guix build -K emacs
	@ build-started /gnu/store/f3gbd1y74vw1my0fmzlpz5cxkqqk423l-emacs-25.3-1.752fba9-checkout.drv - x86_64-linux /var/log/guix/drvs/f3//gbd1y74vw1my0fmzlpz5cxkqqk423l-emacs-25.3-1.752fba9-checkout.drv.bz2
	Initialized empty Git repository in /gnu/store/xrprmz45mi7njni6ypz4mad0ijf02r32-emacs-25.3-1.752fba9-checkout/.git/
	fatal: unable to connect to localhost:
	localhost[0: 127.0.0.1]: errno=Connection refused

	fatal: unable to connect to localhost:
	localhost[0: 127.0.0.1]: errno=Connection refused

	Backtrace:
	           4 (primitive-load "/gnu/store/cq0wvv65l9d7zn515dfg07jg3gr?")
	In ice-9/eval.scm:
	   293:34  3 (_ #<directory (guile-user) 7ce140>)
	In ./guix/build/git.scm:
	    48:10  2 (git-fetch "git://localhost/~ambrevar/projects/emacs" # ?)
	In ./guix/build/utils.scm:
	    589:6  1 (invoke _ . _)
	In unknown file:
	           0 (scm-error misc-error #f "~A ~S" ("program \"/gnu/s?" ?) ?)

I'm not very familiar with the "git" protocol: does it require some
special configuration?

I also tried specifying a local path:

               (url "/home/ambrevar/projects/emacs")

but it seems that Guix' `git-reference` does not like it:

	> guix build -K emacs
	@ build-started /gnu/store/rvadb9sgi9dj0b3hlgpr3l91nbw9vvn0-emacs-25.3-1.752fba9-checkout.drv - x86_64-linux /var/log/guix/drvs/rv//adb9sgi9dj0b3hlgpr3l91nbw9vvn0-emacs-25.3-1.752fba9-checkout.drv.bz2
	Initialized empty Git repository in /gnu/store/xrprmz45mi7njni6ypz4mad0ijf02r32-emacs-25.3-1.752fba9-checkout/.git/
	fatal: '/home/ambrevar/projects/emacs' does not appear to be a git repository
	fatal: Could not read from remote repository.

	Please make sure you have the correct access rights
	and the repository exists.
	fatal: '/home/ambrevar/projects/emacs' does not appear to be a git repository
	fatal: Could not read from remote repository.

	Please make sure you have the correct access rights
	and the repository exists.
	Backtrace:
	           4 (primitive-load "/gnu/store/cq0wvv65l9d7zn515dfg07jg3gr?")
	In ice-9/eval.scm:
	   293:34  3 (_ #<directory (guile-user) 7ce140>)
	In ./guix/build/git.scm:
	    48:10  2 (git-fetch "/home/ambrevar/projects/emacs" "752fba992b?" ?)
	In ./guix/build/utils.scm:
	    589:6  1 (invoke _ . _)
	In unknown file:
	           0 (scm-error misc-error #f "~A ~S" ("program \"/gnu/s?" ?) ?)

I think this is a bug: if git clone accepts local paths, then so should
git-reference.

--
Pierre Neidhardt