Don't permit ref/branch names to end with ".lock"

We already skip over loose refs under $GIT_DIR/refs if the name
ends with ".lock", so creating a branch named "foo.lock" will not
appear in the output of "git branch", "git for-each-ref", nor will
its commit be considered reachable by "git rev-list --all".

In the latter case this is especially evil, as it may cause
repository corruption when objects reachable only through such a
ref are deleted by "git prune".

It should be reasonably safe to deny use of ".lock" as a ref suffix.
In prior versions of Git such branches would be "phantom branches";
you can create it, but you can't see it in "git branch" output.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/Documentation/git-check-ref-format.txt b/Documentation/git-check-ref-format.txt
index d23fd219da..9b707a7030 100644
--- a/Documentation/git-check-ref-format.txt
+++ b/Documentation/git-check-ref-format.txt
@@ -34,6 +34,8 @@ imposes the following rules on how refs are named:
 
 . They cannot end with a slash `/` nor a dot `.`.
 
+. They cannot end with the sequence `.lock`.
+
 . They cannot contain a sequence `@{`.
 
 These rules makes it easy for shell script based tools to parse