git-submodule - make "submodule add" more strict, and document it

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>

1 files changed, 27 insertions, 9 deletions

diff --git a/Documentation/git-submodule.txt b/Documentation/git-submodule.txt
index 105fc2dcd..76702a0a5 100644
--- a/Documentation/git-submodule.txt
+++ b/Documentation/git-submodule.txt
@@ -9,7 +9,7 @@ git-submodule - Initialize, update or inspect submodules
 SYNOPSIS
 --------
 [verse]
-'git submodule' [--quiet] add [-b branch] [--] <repository> [<path>]
+'git submodule' [--quiet] add [-b branch] [--] <repository> <path>
 'git submodule' [--quiet] status [--cached] [--] [<path>...]
 'git submodule' [--quiet] init [--] [<path>...]
 'git submodule' [--quiet] update [--init] [--] [<path>...]
@@ -20,14 +20,31 @@ COMMANDS
 --------
 add::
 	Add the given repository as a submodule at the given path
-	to the changeset to be committed next.  If path is a valid
-	repository within the project, it is added as is. Otherwise,
-	repository is cloned at the specified path. path is added to the
-	changeset and registered in .gitmodules.   If no path is
-	specified, the path is deduced from the repository specification.
-	If the repository url begins with ./ or ../, it is stored as
-	given but resolved as a relative path from the main project's
-	url when cloning.
+	to the changeset to be committed next to the current
+	project: the current project is termed termed the "superproject".
++
+This requires two arguments: <repository> and <path>.
++
+<repository> is the URL of the new submodule's origin repository.
+This may be either an absolute URL, or (if it begins with ./
+or ../), the location relative to the superproject's origin
+repository.
++
+<path> is the relative location for the cloned submodule to
+exist in the superproject. If <path> does not exist, then the
+submodule is created by cloning from the named URL. If <path> does
+exist and is already a valid git repository, then this is added
+to the changeset without cloning. This second form is provided
+to ease creating a new submodule from scratch, and presumes
+the user will later push the submodule to the given URL.
++
+In either case, the given URL is recorded into .gitmodules for
+use by subsequent users cloning the superproject. If the URL is
+given relative to the superproject's repository, the presumption
+is the superproject and submodule repositories will be kept
+together in the same relative location, and only the
+superproject's URL need be provided: git-submodule will correctly
+locate the submodule using the relative URL in .gitmodules.
 
 status::
 	Show the status of the submodules. This will print the SHA-1 of the
@@ -85,6 +102,7 @@ OPTIONS
 <path>::
 	Path to submodule(s). When specified this will restrict the command
 	to only operate on the submodules found at the specified paths.
+	(This argument is required with add).
 
 FILES
 -----