range-diff: optionally accept pathspecs

The `git range-diff` command can be quite expensive, which is not a
surprise given that the underlying algorithm to match up pairs of
commits between the provided two commit ranges has a cubic runtime.

Therefore it makes sense to restrict the commit ranges as much as
possible, to reduce the amount of input to that O(N^3) algorithm.

In chatty repositories with wide trees, this is not necessarily
possible merely by choosing commit ranges wisely.

Let's give users another option to restrict the commit ranges: by
providing a pathspec. That helps in repositories with wide trees because
it is likely that the user has a good idea which subset of the tree they
are actually interested in.

Example:

	git range-diff upstream/main upstream/seen HEAD -- range-diff.c

This shows commits that are either in the local branch or in `seen`, but
not in `main`, skipping all commits that do not touch `range-diff.c`.

Note: Since we piggy-back the pathspecs onto the `other_arg` mechanism
that was introduced to be able to pass through the `--notes` option to
the revision machinery, we must now ensure that the `other_arg` array is
appended at the end (the revision range must come before the pathspecs,
if any).

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 12 insertions, 1 deletions

diff --git a/t/t3206-range-diff.sh b/t/t3206-range-diff.sh
index d12e4e4cc6..459beaf7d9 100755
--- a/t/t3206-range-diff.sh
+++ b/t/t3206-range-diff.sh
@@ -162,7 +162,7 @@ test_expect_success 'A^! and A^-<n> (unmodified)' '
 '
 
 test_expect_success 'A^{/..} is not mistaken for a range' '
-	test_must_fail git range-diff topic^.. topic^{/..} 2>error &&
+	test_must_fail git range-diff topic^.. topic^{/..} -- 2>error &&
 	test_i18ngrep "not a commit range" error
 '
 
@@ -772,6 +772,17 @@ test_expect_success '--left-only/--right-only' '
 	test_cmp expect actual
 '
 
+test_expect_success 'ranges with pathspecs' '
+	git range-diff topic...mode-only-change -- other-file >actual &&
+	test_line_count = 2 actual &&
+	topic_oid=$(git rev-parse --short topic) &&
+	mode_change_oid=$(git rev-parse --short mode-only-change^) &&
+	file_change_oid=$(git rev-parse --short mode-only-change) &&
+	grep "$mode_change_oid" actual &&
+	! grep "$file_change_oid" actual &&
+	! grep "$topic_oid" actual
+'
+
 test_expect_success 'submodule changes are shown irrespective of diff.submodule' '
 	git init sub-repo &&
 	test_commit -C sub-repo sub-first &&