Re: [PATCH] diffcore: add a filter to find a specific blob

[Stefan Beller <sbeller@google.com>]

On Thu, Dec 14, 2017 at 1:22 PM, Jonathan Nieder <jrnieder@gmail.com> wrote:

> - what about mode changes?  If the file became executable but the
>   blob content didn't change, does that commit match?

./git log --find-object=$(git rev-parse ba67504f:t/perf/p3400-rebase.sh)

claims it does find the mode change (commit ba67504f is just a mode
change)

> - are copies and renames shown (if I am passing -M -C)?

It restricts the commits shown, not the renamed files. But I assume
you mean it the same way as with mode changes.
I did not find a good commit in gits history to demonstrate, but as
it is orthogonal to the object id restrictions, I would think it works

> Nit, not related to this change: it would be nice to have a long
> option to go along with the short name '-t' --- e.g. --include-trees.

follow up patches welcome. :)

>
> Another nit: s/gitlink entry/submodule commit/, perhaps.  The commit
> object is not a gitlink entry: it is pointed to by a gitlink entry.

Well, what if the user doesn't have a submodule, but uses gitlinks
for other purposes? We do inspect the gitlink, so it is correct IMHO.

> Another documentation idea: it may be nice to point out that this
> is only about the preimage and postimage submodule commit and that
> it doesn't look at the history in between.

That is sensible. One might be tempted to ask: "Which superproject
commit contains a submodule pointer, that has commit $X in the
submodule history?", but this new option is totally not answering this.

>>                                                          The
>> reason why these commits both occur prior to v2.0.0 are evil
>> merges that are not found using this new mechanism.
>
> Would it be worth the doc mentioning that this doesn't look at merges
> unless you use one of the -m/-c/--cc options, or does that go without
> saying?

I assumed it goes without saying, just like the lacking -t could mean
to ignore trees. ;)


>
> [...]
>> --- a/Documentation/diff-options.txt
>> +++ b/Documentation/diff-options.txt
>> @@ -500,6 +500,12 @@ information.
>>  --pickaxe-regex::
>>       Treat the <string> given to `-S` as an extended POSIX regular
>>       expression to match.
>> +
>> +--find-object=<object-id>::
>> +     Restrict the output such that one side of the diff
>> +     matches the given object id. The object can be a blob,
>> +     gitlink entry or tree (when `-t` is given).
>
> I like this name --find-object more than --blobfind!  I am not sure it
> quite matches what the user is looking for, though.  We are not
> looking for all occurences of the object; we only care about when the
> object appears (was added or removed) in the diff.

Thanks! Yes, but the 'edges' are so few commits that a further walk
will reveal all you need to know?


>
> Putting it in context, we have:
>
>         pickaxe options:
>         -S: detect changes in occurence count of a string
>         -G: grep lines in diff for a string
>
>         --pickaxe-all:
>                 do not filter the diff when the patch matches pickaxe
>                 conditions.
>
>                 kind of like log --full-diff, but restricted to pickaxe
>                 options.
>         --pickaxe-regex: treat -S argument as a regex, not a string
>
> Is this another kind of pickaxe option?  It feels similar to -S, but
> at an object level instead of a substring level, so in a way it would
> be appealing to call it --pickaxe-object.  Does --pickaxe-all affect
> it like it affects -S and -G?
>
> Another context to put it in is:
>
>         --diff-filter:
>                 limit paths (but not commits?) to those with a change
>                 matching optarg
>
> If I understand correctly, then --diff-filter does not interact with
> --pickaxe-all, or in other words it is a different filtering
> condition.  Is this another kind of diff filter?  In that context, it
> may be appealing to call it something like --object-filter.
>
> --diff-filter is an example where it seems appealing to have a
> --full-diff option to diff-tree that could apply to all filters and
> not just pickaxe.
>
> [... implementation snipped ...]
>
> The implementation looks lovely and I'm especially happy about the
> tests.  Thanks for writing it.
>
> Thoughts?
> Jonathan

Regarding finding a better name, I would want to hear from others,
I am happy with --find-object, though I can see --pickaxe-object
or --object--filter to be a good narrative as well.

Stefan