Re: [PATCH] git clone depth of 0 not possible.

From: Matthijs Kooijman <matthijs@stdin.nl>
Date: Jul 9, 2013, 13:35 UTC
Message-ID: <20130709133542.GJ10217@login.drsnuggles.stderr.nl>
In-Reply-To: <7va9nf2fyp.fsf@alter.siamese.dyndns.org>

Hi Junio,

Show 19 quoted lines

> Doing it "correctly" (in the shorter term) would involve:
> 
>  - adding a capability on the sending side "fixed-off-by-one-depth"
>    to the protocol, and teaching the sending side to advertise the
>    capability;
>    
>  - teaching the requestor that got --depth=N from the end user to
>    pay attention to the new capability in such a way that:
> 
>    - when talking to an old sender (i.e. without the off-by-one
>      fix), send N-1 for N greater than 1.  Punt on N==1;
> 
>    - when talking to a fixed sender, ask to enable the capability,
>      and send N as is (including N==1).
> 
>  - teaching the sending side to see if the new behaviour to fix
>    off-by-one is asked by the requestor, and stop at the correct
>    number of commits, not oversending one more.  Otherwise retain
>    the old behaviour.

While implementing the above, I noticed my fix now introduced an off-by-one error the other way. When investigating, I found this commit:

	commit 682c7d2f1a2d1a5443777237450505738af2ff1a
	Author: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
	Date:   Fri Jan 11 16:05:47 2013 +0700

	    upload-pack: fix off-by-one depth calculation in shallow clone

	    get_shallow_commits() is used to determine the cut points at a given
	    depth (i.e. the number of commits in a chain that the user likes to
	    get). However we count current depth up to the commit "commit" but we
	    do the cutting at its parents (i.e. current depth + 1). This makes
	    upload-pack always return one commit more than requested. This patch
	    fixes it.

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

Which actually seems to fix the off-by-one bug that is described in this thread, but without going through the hoops of preserving current behaviour for older git versions (that is, it makes behaviour dependent on server version instead of client version).

Does this mean the discussion in this thread is meaningless, or is that commit not intended to be the final fix?

In any case, IIUC that particular patch makes a piece of the existing code dead, which needs to be removed.

Gr.

Matthijs