On 05/29/2013 06:18 PM, Junio C Hamano wrote:
> Michael Haggerty <mhag...@alum.mit.edu> writes:
>> The old version copied one entry to its destination position, then
>> deleted any matching entries from the tail of the array.  This
>> required the tail of the array to be copied multiple times.  It didn't
>> affect the complexity of the algorithm because the whole tail has to
>> be searched through anyway.  But all the copying was unnecessary.
>> Instead, check for the existence of an entry with the same name in the
>> *head* of the list before copying an entry to its final position.
>> This way each entry has to be copied at most one time.
>> Extract a helper function contains_name() to do a bit of the work.
>> Signed-off-by: Michael Haggerty <mhag...@alum.mit.edu>
>> ---
>>  object.c | 32 +++++++++++++++++++++-----------
>>  object.h |  6 +++++-
>>  2 files changed, 26 insertions(+), 12 deletions(-)
>> diff --git a/object.c b/object.c
>> index fcd4a82..10b5349 100644
>> --- a/object.c
>> +++ b/object.c
>> @@ -294,22 +294,32 @@ void object_array_filter(struct object_array *array,
>>      array->nr = dst;
>>  }
>> +/*
>> + * Return true iff array already contains an entry with name.
>> + */
>> +static int contains_name(struct object_array *array, const char *name)
>> +{
>> +    unsigned nr = array->nr, i;
>> +    struct object_array_entry *object = array->objects;
>> +
>> +    for (i = 0; i < nr; i++, object++)
>> +            if (!strcmp(object->name, name))
>> +                    return 1;
>> +    return 0;
>> +}
> Because some codepaths (e.g. patch 14/25) stuff NULL in the name
> field, we may want to be more careful with this.
> This is not a new problem, and I think the longer term solution is
> to get rid of object_array_remove_duplicates(), so it is perfectly
> fine to leave this function broken with respect to NULL input as-is.

You make a good point about NULL names, but I agree to leave it for now
since it needs work anyway.

> The only caller of remove-duplicates is bundle.c, which gets many
> starting points and end points from the command line and tries to be
> nice by removing obvious duplicates, e.g.
>       git bundle create t.bundle master master
> but I think its logic of deduping is wrong.  It runs dwim_ref() on
> the incoming refs after the remove-duplicates call, so
>       git bundle create t.bundle master heads/mater
> will end up with two copies of refs/heads/master.  To fix it, the
> code must dedup the result of running dwim_ref(), and at that point,
> there is no reason to call object_array_remove_duplicates().

That sounds reasonable.

I poked around this code a bit to understand what is going on, and it
occurred to me that the object_array can include both positive and
negative references, right?  And yet object_array_remove_duplicates()
only considers names, not flags.  So it seems to me that if the deduping
code would see the same reference twice, once positive and once
negative, then it would throw an arbitrary one of them out, which would
be wrong.

But I couldn't provoke this situation, so perhaps setup_revisions()
already specially treats combinations like "master ^master"?  (If that's
true then why? and wouldn't it get confused by "master ^heads/master"?)

I suppose someday I will have to dig into these functions and maybe even
document them.


Michael Haggerty
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