From mboxrd@z Thu Jan  1 00:00:00 1970
From: Junio C Hamano <gitster@pobox.com>
Subject: Re: [PATCH] Fix segfault in merge-recursive
Date: Fri, 08 May 2009 16:36:16 -0700
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Cc: Dave O <cxreg@pobox.com>, git@vger.kernel.org
To: Johannes Schindelin <Johannes.Schindelin@gmx.de>
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In-Reply-To: <alpine.DEB.1.00.0905082229520.4601@intel-tinevez-2-302> (Johannes Schindelin's message of "Fri\, 8 May 2009 22\:30\:32 +0200 \(CEST\)")
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Johannes Schindelin <Johannes.Schindelin@gmx.de> writes:

> When there is no "common" tree (for whatever reason), we must not
> throw a segmentation fault.

You described why the old code was wrong (i.e. "init_tree_desc_from_tree
is called with common == NULL"), but there is no mention why the new code
is correct.  For the purpose of satisfying the above statement, you could
have just exit(0) as well ;-)

> +	else {
> +		opts.merge = 0;
> +		opts.head_idx = 1;
> +		init_tree_desc_from_tree(t+0, head);
> +		init_tree_desc_from_tree(t+1, merge);
> +		rc = unpack_trees(2, t, &opts);
> +	}

This looks more like a half of branch-switch from HEAD to MERGE, not a
merge between HEAD and MERGE as two equal histories.  Shouldn't it be
doing a three-way tree merge using an empty tree object as the common
ancestor instead, just like merge_recursive.c::merge_recursive() itself
does?