Mark Levedahl authored Jul 09, 2008 and Junio C Hamano committed Jul 14, 2008

This change makes "submodule add" much more strict in the arguments it
takes, and is intended to address confusion as recently noted on the
git-list. With this change, the required syntax is:

	$ git submodule add URL path

Specifically, this eliminates the form

	$ git submodule add URL

which was confused by more than one person as

	$ git submodule add path

With this patch, the URL locating the submodule's origin repository can be
either an absolute URL, or (if it begins with ./ or ../) can express the
submodule's repository location relative to the superproject's origin.

This patch also eliminates a third form of URL, which was relative to the
superproject's top-level directory (not its repository).  Any URL that was
neither absolute nor matched ./*|../* was assumed to point to a
subdirectory of the superproject as the location of the submodule's origin
repository.  This URL form was confusing and does not seem to correspond
to an important use-case.  Specifically, no-one has identified the need to
clone from a repository already in the superproject's tree, but if this is
needed it is easily done using an absolute URL: $(pwd)/relative-path.  So,
no functionality is lost with this patch. (t6008-rev-list-submodule.sh did
rely upon this relative URL, fixed by using $(pwd).)

Following this change, there are exactly four variants of
submodule-add, as both arguments have two flavors:

URL can be absolute, or can begin with ./|../ and thus names the
submodule's origin relative to the superproject's origin.

Note: With this patch, "submodule add" discerns an absolute URL as
matching /*|*:*: e.g., URL begins with /, or it contains a :.  This works
for all valid URLs, an absolute path in POSIX, as well as an absolute path
on Windows).

path can either already exist as a valid git repo, or will be cloned from
the given URL.  The first form here eases creation of a new submodule in
an existing superproject as the submodule can be added and tested in-tree
before pushing to the public repository.  However, the more usual form is
the second, where the repo is cloned from the given URL.

This specifically addresses the issue of

	$ git submodule add a/b/c

attempting to clone from a repository at "a/b/c" to create a new module
in "c". This also simplifies description of "relative URL" as there is now
exactly *one* form: a URL relative to the parent's origin repo.

Signed-off-by: Mark Levedahl <mlevedahl@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>