Re: [PATCH] name-rev: use generation numbers if available

[Derrick Stolee <derrickstolee@github.com>]

On 2/28/2022 3:20 PM, Keller, Jacob E wrote:
> On 2/28/2022 11:50 AM, Derrick Stolee wrote:
>> On 2/28/2022 2:07 PM, Jacob Keller wrote:
>>> From: Jacob Keller <jacob.keller@gmail.com>
>>> +/* Check if a commit is before the cutoff. Prioritize generation numbers
>>> + * first, but use the commit timestamp if we lack generation data.
>>> + */
>>> +static int commit_is_before_cutoff(struct commit *commit)
>>> +{
>>> +	if (generation_cutoff < GENERATION_NUMBER_INFINITY)
>>> +		return commit_graph_generation(commit) < generation_cutoff;
>>> +
>>> +	return commit->date < cutoff;
>>> +}
>>
>> There are two subtle things going on here when generation_cutoff is
>> zero:
>>
>> 1. In a commit-graph with topological levels _or_ generation numbers v2,
>>    commit_graph_generation(commit) will always be positive, so we don't
>>    need to do the lookup.
> 
> I.e. once we have a generation_cutoff of 0 we can just completely bypass
> the lookup, saving some time.
> 
> I think we can do "return generation_cutoff &&
> commit_graph_generation(commit) < generation_cutoff"
> 
>>
>> 2. If the commit-graph was written by an older Git version before
>>    topological levels were implemented, then the generation of commits
>>    in the commit-graph are all zero(!). This means that the logic here
>>    would be incorrect for the "all" case.
>>
>> The fix for both cases is to return 1 if generation_cutoff is zero:
>>
> 
> I think you mean return 0? Because this returns true if the commit is
> before the cutoff, but false if its not. (i.e. if its true, we should
> stop searching this commit, but if its false we should continue searching?

Yes, sorry I had it mixed up. Your generation_cutoff && ... approach
will work in that case.

>>> +test_expect_success 'name-rev --all works with non-monotonic' '
>>
>> This is working because of the commit-graph, right? We still have
>> it from the previous test, so we aren't testing that this works
>> when we only have the commit date as a cutoff.
>>
> 
> I can either extend this test or add a separate test which covers this.
> The test failed before I added the commit graph line.
> 
>>> +	(
>>> +		cd non-monotonic &&
>>> +
>>> +		cat >expect <<-\EOF &&
>>> +		E
>>> +		D
>>> +		D~1
>>> +		D~2
>>> +		A
>>> +		EOF
>>> +
>>> +		git log --pretty=%H >revs &&
>>> +		git name-rev --tags --annotate-stdin --name-only <revs >actual &&
>>> +
>>> +		test_cmp expect actual
>>> +	)
>>
>> Do you want to include a test showing the "expected" behavior
>> when there isn't a commit-graph file? You might need to delete
>> an existing commit-graph (it will exist in the case of
>> GIT_TEST_COMMIT_GRAPH=1).
>>
> 
> This test actually is intended to show that it works regardless of
> whether we have a commit graph. (Because in --annotate-stdin mode we
> disable the heuristic since we don't know what commits we'll see in advance)
> 
> Is there a good way to delete the graph file?

The basic way is "rm -rf .git/info/commit-graph*" to be absolutely
sure (there might be an incremental commit-graph which appears as
a "commit-graphs" directory).
 
>> I also see that you intended to test the "--all" option, which
>> is not included in your test. That's probably the real key to
>> getting this test to work correctly. Deleting the graph will
>> probably cause a failure on this test unless "--all" is added.
>>
> 
> Actually both --all and --annotate-stdin disable the heuristic. However,
> I think adding a test for both makes sense.

Ah. OK. They could be assertions within the same test since the
output is expected to be the same.

Thanks,
-Stolee