fetch: add --unshallow for turning shallow repo into complete one

The user can do --depth=2147483647 (*) for restoring complete repo
now. But it's hard to remember. Any other numbers larger than the
longest commit chain in the repository would also do, but some
guessing may be involved. Make easy-to-remember --unshallow an alias
for --depth=2147483647.

Make upload-pack recognize this special number as infinite depth. The
effect is essentially the same as before, except that upload-pack is
more efficient because it does not have to traverse to the bottom
anymore.

The chance of a user actually wanting exactly 2147483647 commits
depth, not infinite, on a repository with a history that long, is
probably too small to consider. The client can learn to add or
subtract one commit to avoid the special treatment when that actually
happens.

(*) This is the largest positive number a 32-bit signed integer can
    contain. JGit and older C Git store depth as "int" so both are OK
    with this number. Dulwich does not support shallow clone.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/Documentation/git-fetch-pack.txt b/Documentation/git-fetch-pack.txt
index 8c75120..b81e90d 100644
--- a/Documentation/git-fetch-pack.txt
+++ b/Documentation/git-fetch-pack.txt
@@ -84,6 +84,8 @@ be in a separate packet, and the list must end with a flush packet.
 
 --depth=<n>::
 	Limit fetching to ancestor-chains not longer than n.
+	'git-upload-pack' treats the special depth 2147483647 as
+	infinite even if there is an ancestor-chain that long.
 
 --no-progress::
 	Do not show the progress.