Jacob Keller <jacob.keller@xxxxxxxxx> writes:
> On Thu, Nov 2, 2017 at 10:18 PM, Junio C Hamano <gitster@xxxxxxxxx> wrote:
>> ...
>> It is easy to imagine that we can restrict "git log" traversal with
>> a "--blobchange=<blob>" option instead of (or in addition to) the
>> limitation <pathspec> gives us. Instead of treating a commit whose
>> diff against its parent commit has any filepair that is different
>> within <pathspec> as "!TREESAME", we can treat a commit whose diff
>> against its parent commit has a filepair that has the <blob> on
>> either side of the filepair as "!TREESAME" (in other words, we
>> ignore a transition that is not about introducing or forgetting the
>> <blob> we are looking for as an "interesting change"). That would
>> give you a commit history graph in which only (and all) such commits
>> that either adds or removes the <blob> in it.
>>
>> Hmm?
>
> This seems quite useful in the context of figuring out how a file got
> to such a state. This is useful to me, since if I know the state of a
> file (ie: it's exact contents) I can determine the blob name, and then
> use that to lookup where it was introduced.
This is probably a bit harder than an average #leftoverbits, but if
somebody wants to get their hands dirty, it should be reasonably
straightforward. The needed changes would roughly go like so:
- Add "struct oid *blob_change;" to diff_options, initialized to
NULL.
- Teach diff_opt_parse() a new option "--blobchange=<blob>".
Allocate a struct oid when you parse this option and point at it
with the blob_change field above.
- Write diffcore-blobchange.c, modeled after diffcore-pickaxe.c,
but this should be a lot simpler (as there is no need for an
equivalent for "pickaxe-all" option). It would
- prepare an empty diff_queue_struct "outq";
- iterate over the given diff_queue "q", and
- a filepair p whose p->one is blob_change and p->two is not,
(or the other way around) is added to outq with diff_q()
- a filepair whose p->one/p->two do not involve blob_change
is freed with diff_free_filepair().
- replace "q" with "outq".
- Add a call to diffcore_blobchange() early in diffcore_std(),
probably immediately after skip-stat-unmatch, when blob_change
field is not NULL.
- Arrange that blob_change is propagated to revs->pruning in
setup_revisions().
