rm: better document side effects when removing a submodule

The "Submodules" section of the "git rm" documentation mentions what will
happen when a submodule with a gitfile gets removed with newer git. But it
doesn't talk about what happens when the user changes between commits
before and after the removal, which does not remove the submodule from the
work tree like using the rm command did the first time.

Explain what happens and what the user has to do manually to fix that in
the new BUGS section. Also document this behavior in a new test.

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

1 files changed, 9 insertions, 0 deletions

diff --git a/Documentation/git-rm.txt b/Documentation/git-rm.txt
index 9d731b453..f1efc116e 100644
--- a/Documentation/git-rm.txt
+++ b/Documentation/git-rm.txt
@@ -170,6 +170,15 @@ of files and subdirectories under the `Documentation/` directory.
 	(i.e. you are listing the files explicitly), it
 	does not remove `subdir/git-foo.sh`.
 
+BUGS
+----
+Each time a superproject update removes a populated submodule
+(e.g. when switching between commits before and after the removal) a
+stale submodule checkout will remain in the old location. Removing the
+old directory is only safe when it uses a gitfile, as otherwise the
+history of the submodule will be deleted too. This step will be
+obsolete when recursive submodule update has been implemented.
+
 SEE ALSO
 --------
 linkgit:git-add[1]