patchline-log: fix crash when --first-parent is used

> line-log tries to access all parents of a commit, but only the first
> parent has been loaded if "--first-parent" is specified, resulting
> in a crash.
>
> Limit the number of parents to one if "--first-parent" is specified.
>
> Reported-by: Eric N. Vander Weele <ericvw@gmail.com>
> Signed-off-by: Tzvetan Mikov <tmikov@gmail.com>
> ---

>  line-log.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/line-log.c b/line-log.c
> index 1008e72..86e7274 100644
> --- a/line-log.c
> +++ b/line-log.c
> @@ -1141,6 +1141,9 @@ static int process_ranges_merge_commit(struct rev_info *rev, struct commit *comm
>  	int i;
>  	int nparents = commit_list_count(commit->parents);
>  
> +	if (nparents > 1 && rev->first_parent_only)
> +	    nparents = 1;
> +
>  	diffqueues = xmalloc(nparents * sizeof(*diffqueues));
>  	cand = xmalloc(nparents * sizeof(*cand));
>  	parents = xmalloc(nparents * sizeof(*parents));

>> line-log tries to access all parents of a commit, but only the first
>> parent has been loaded if "--first-parent" is specified, resulting
>> in a crash.
>>
>> Limit the number of parents to one if "--first-parent" is specified.
>>

> On Mon, Nov 3, 2014 at 12:58 PM, Junio C Hamano <gitster@pobox.com> wrote:
> 
>>> line-log tries to access all parents of a commit, but only the first
>>> parent has been loaded if "--first-parent" is specified, resulting
>>> in a crash.
>>>
>>> Limit the number of parents to one if "--first-parent" is specified.
>>>
> 
>> [...]
>> Tzvetan, can we have a test for this one?
> 
> Here is a sequence of commands to reproduce the crash:
> 
> git init
> echo "1" > a.txt && git add a.txt && git commit -m "a"
> git checkout -b branch
> echo "2" > b.txt && git add b.txt && git commit -m "b"
> git checkout master
> git merge branch --no-ff -m "merge"
> git log --first-parent -L 1,1:a.txt
> 
> I am not sure whether you have a requirement for a formal test
> included with the patch, but if there is one, I am happy to
> rework it.
> 
> This is a very simple fix for the crash, though possibly
> a "real" comprehensive fix may be needed. I am not sure.
> The real cause is that with "--first-parent" some commit
> objects are never loaded from disk but may still be accessed.
> 
> (sorry about my formatting - have to use GMail)
> 
> regards,
> Tzvetan
> 

> line-log tries to access all parents of a commit, but only the first
> parent has been loaded if "--first-parent" is specified, resulting
> in a crash.
>
> Limit the number of parents to one if "--first-parent" is specified.
>
> Reported-by: Eric N. Vander Weele <ericvw@gmail.com>
> Signed-off-by: Tzvetan Mikov <tmikov@gmail.com>
> ---
>  PATCH v2: Add a test case (thanks Michael J Gruber)

>  line-log.c          | 3 +++
>  t/t4211-line-log.sh | 5 +++++
>  2 files changed, 8 insertions(+)
>
> diff --git a/line-log.c b/line-log.c
> index 1008e72..86e7274 100644
> --- a/line-log.c
> +++ b/line-log.c
> @@ -1141,6 +1141,9 @@ static int process_ranges_merge_commit(struct rev_info *rev, struct commit *comm
>  	int i;
>  	int nparents = commit_list_count(commit->parents);
>  
> +	if (nparents > 1 && rev->first_parent_only)
> +	    nparents = 1;
> +
>  	diffqueues = xmalloc(nparents * sizeof(*diffqueues));
>  	cand = xmalloc(nparents * sizeof(*cand));
>  	parents = xmalloc(nparents * sizeof(*parents));
> diff --git a/t/t4211-line-log.sh b/t/t4211-line-log.sh
> index 7369d3c..0901b30 100755
> --- a/t/t4211-line-log.sh
> +++ b/t/t4211-line-log.sh
> @@ -94,4 +94,9 @@ test_expect_success '-L ,Y (Y == nlines + 2)' '
>  	test_must_fail git log -L ,$n:b.c
>  '
>  
> +test_expect_success '-L with --first-parent and a merge' '
> +	git checkout parallel-change &&
> +	git log --first-parent -L 1,1:b.c
> +'
> +
>  test_done