Re: [PATCH 2/2] blame: enable and test the sparse index

> On Thu, Oct 14, 2021 at 10:25 AM Lessley Dennington via GitGitGadget
> <gitgitgadget@gmail.com> wrote:
>>
>> From: Lessley Dennington <lessleydennington@gmail.com>
>>
>> Enable the sparse index for the 'git blame' command. The index was already
>> not expanded with this command, so the most interesting thing to do is to
>> add tests that verify that 'git blame' behaves correctly when the sparse
>> index is enabled and that its performance improves. More specifically, these
>> cases are:
>>
>> 1. The index is not expanded for 'blame' when given paths in the sparse
>> checkout cone at multiple levels.
>>
>> 2. Performance measurably improves for 'blame' with sparse index when given
>> paths in the sparse checkout cone at multiple levels.
>>
>> The `p2000` tests demonstrate a ~60% execution time reduction when running
>> 'blame' for a file two levels deep and and a ~30% execution time reduction
>> for a file three levels deep.
>>
>> Test                                         before  after
>> ----------------------------------------------------------------
>> 2000.62: git blame f2/f4/a (full-v3)         0.31    0.32 +3.2%
>> 2000.63: git blame f2/f4/a (full-v4)         0.29    0.31 +6.9%
>> 2000.64: git blame f2/f4/a (sparse-v3)       0.55    0.23 -58.2%
>> 2000.65: git blame f2/f4/a (sparse-v4)       0.57    0.23 -59.6%
>> 2000.66: git blame f2/f4/f3/a (full-v3)      0.77    0.85 +10.4%
>> 2000.67: git blame f2/f4/f3/a (full-v4)      0.78    0.81 +3.8%
>> 2000.68: git blame f2/f4/f3/a (sparse-v3)    1.07    0.72 -32.7%
>> 2000.99: git blame f2/f4/f3/a (sparse-v4)    1.05    0.73 -30.5%
> 
> Looks good.
> 
>> We do not include paths outside the sparse checkout cone because blame
>> currently does not support blaming files outside of the sparse definition.
>> Attempting to do so fails with the following error:
>>
>> fatal: no such path '<path outside sparse definition>' in HEAD
> 
> While technically accurate, this wording is misleading; it implies
> that there is something unique to sparse checkouts, and perhaps even
> to cone mode, affecting how blame handles files not in the working
> directory.  That's not true, though; git blame without a revision has
> always reported an error when given a file that does not exist in the
> working tree.  Try this in git.git:
> 
> $ rm t/README
> $ git blame t/README
> fatal: Cannot lstat 't/README': No such file or directory
> 
> The reason is that with no revisions, calling git blame with a
> filename means asking the question "Which commit did each line in that
> file come from?"  If there's no file, the question just doesn't make
> sense.  You could make sense of it by thinking in terms of some
> revision of the file, but then you're passing a revision along --
> which works just fine in a sparse checkout too.
> 

>>
>> Signed-off-by: Lessley Dennington <lessleydennington@gmail.com>
>> ---
>>   builtin/blame.c                          |  3 +++
>>   t/perf/p2000-sparse-operations.sh        |  2 ++
>>   t/t1092-sparse-checkout-compatibility.sh | 24 +++++++++++++++++-------
>>   3 files changed, 22 insertions(+), 7 deletions(-)
>>
>> diff --git a/builtin/blame.c b/builtin/blame.c
>> index 641523ff9af..af3d81e2bd4 100644
>> --- a/builtin/blame.c
>> +++ b/builtin/blame.c
>> @@ -902,6 +902,9 @@ int cmd_blame(int argc, const char **argv, const char *prefix)
>>          long anchor;
>>          const int hexsz = the_hash_algo->hexsz;
>>
>> +       prepare_repo_settings(the_repository);
>> +       the_repository->settings.command_requires_full_index = 0;
>> +
>>          setup_default_color_by_age();
>>          git_config(git_blame_config, &output_option);
>>          repo_init_revisions(the_repository, &revs, NULL);
>> diff --git a/t/perf/p2000-sparse-operations.sh b/t/perf/p2000-sparse-operations.sh
>> index bff93f16e93..9ac76a049b8 100755
>> --- a/t/perf/p2000-sparse-operations.sh
>> +++ b/t/perf/p2000-sparse-operations.sh
>> @@ -115,5 +115,7 @@ test_perf_on_all git reset --hard
>>   test_perf_on_all git reset -- does-not-exist
>>   test_perf_on_all git diff
>>   test_perf_on_all git diff --staged
>> +test_perf_on_all git blame $SPARSE_CONE/a
>> +test_perf_on_all git blame $SPARSE_CONE/f3/a
>>
>>   test_done
>> diff --git a/t/t1092-sparse-checkout-compatibility.sh b/t/t1092-sparse-checkout-compatibility.sh
>> index 1070bff1a83..54826e858a9 100755
>> --- a/t/t1092-sparse-checkout-compatibility.sh
>> +++ b/t/t1092-sparse-checkout-compatibility.sh
>> @@ -485,15 +485,16 @@ test_expect_success 'blame with pathspec inside sparse definition' '
>>          test_all_match git blame deep/deeper1/deepest/a
>>   '
>>
>> -# TODO: blame currently does not support blaming files outside of the
>> -# sparse definition. It complains that the file doesn't exist locally.
>> -test_expect_failure 'blame with pathspec outside sparse definition' '
>> +# Blame does not support blaming files outside of the sparse
>> +# definition, so we verify this scenario.
> 
> As above, this is misleading.  It'd be better to word it something like:
> 
> # Without a revision specified, blame will error if passed any file that
> # is not present in the working directory (even if the file is tracked).
> # Here we just verify that this is also true with sparse checkouts.
> 

>> +test_expect_success 'blame with pathspec outside sparse definition' '
>>          init_repos &&
>>
>> -       test_all_match git blame folder1/a &&
>> -       test_all_match git blame folder2/a &&
>> -       test_all_match git blame deep/deeper2/a &&
>> -       test_all_match git blame deep/deeper2/deepest/a
>> +       test_sparse_match git sparse-checkout set &&
>> +       test_sparse_match test_must_fail git blame folder1/a &&
>> +       test_sparse_match test_must_fail git blame folder2/a &&
>> +       test_sparse_match test_must_fail git blame deep/deeper2/a &&
>> +       test_sparse_match test_must_fail git blame deep/deeper2/deepest/a
>>   '
>>
>>   test_expect_success 'checkout and reset (mixed)' '
>> @@ -871,6 +872,15 @@ test_expect_success 'sparse-index is not expanded: merge conflict in cone' '
>>          )
>>   '
>>
>> +test_expect_success 'sparse index is not expanded: blame' '
>> +       init_repos &&
>> +
>> +       ensure_not_expanded blame a &&
>> +       ensure_not_expanded blame deep/a &&
>> +       ensure_not_expanded blame deep/deeper1/a &&
>> +       ensure_not_expanded blame deep/deeper1/deepest/a
>> +'
>> +
>>   # NEEDSWORK: a sparse-checkout behaves differently from a full checkout
>>   # in this scenario, but it shouldn't.
>>   test_expect_success 'reset mixed and checkout orphan' '
>> --
>> gitgitgadget