submodule: teach rm to remove submodules unless they contain a git directory

Currently using "git rm" on a submodule - populated or not - fails with
this error:

	fatal: git rm: '<submodule path>': Is a directory

This made sense in the past as there was no way to remove a submodule
without possibly removing unpushed parts of the submodule's history
contained in its .git directory too, so erroring out here protected the
user from possible loss of data.

But submodules cloned with a recent git version do not contain the .git
directory anymore, they use a gitfile to point to their git directory
which is safely stored inside the superproject's .git directory. The work
tree of these submodules can safely be removed without losing history, so
let's teach git to do so.

Using rm on an unpopulated submodule now removes the empty directory from
the work tree and the gitlink from the index. If the submodule's directory
is missing from the work tree, it will still be removed from the index.

Using rm on a populated submodule using a gitfile will apply the usual
checks for work tree modification adapted to submodules (unless forced).
For a submodule that means that the HEAD is the same as recorded in the
index, no tracked files are modified and no untracked files that aren't
ignored are present in the submodules work tree (ignored files are deemed
expendable and won't stop a submodule's work tree from being removed).
That logic has to be applied in all nested submodules too.

Using rm on a submodule which has its .git directory inside the work trees
top level directory will just error out like it did before to protect the
repository, even when forced. In the future git could either provide a
message informing the user to convert the submodule to use a gitfile or
even attempt to do the conversion itself, but that is not part of this
change.

Signed-off-by: Jens Lehmann <Jens.Lehmann@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 15 insertions, 0 deletions

diff --git a/Documentation/git-rm.txt b/Documentation/git-rm.txt
index 5d31860..882cb11 100644
--- a/Documentation/git-rm.txt
+++ b/Documentation/git-rm.txt
@@ -107,6 +107,21 @@ as well as modifications of existing paths.
 Typically you would first remove all tracked files from the working
 tree using this command:
 
+Submodules
+~~~~~~~~~~
+Only submodules using a gitfile (which means they were cloned
+with a git version 1.7.8 or newer) will be removed from the work
+tree, as their repository lives inside the .git directory of the
+superproject. If a submodule (or one of those nested inside it)
+still uses a .git directory, `git rm` will fail - no matter if forced
+or not - to protect the submodule's history.
+
+A submodule is considered up-to-date when the HEAD is the same as
+recorded in the index, no tracked files are modified and no untracked
+files that aren't ignored are present in the submodules work tree.
+Ignored files are deemed expendable and won't stop a submodule's work
+tree from being removed.
+
 ----------------
 git ls-files -z | xargs -0 rm -f
 ----------------