branch: clean up commit flags after merge-filter walk

When we run `branch --merged`, we use prepare_revision_walk
with the merge-filter marked as UNINTERESTING. Any branch
tips that are marked UNINTERESTING after it returns must be
ancestors of that commit. As we iterate through the list of
refs to show, we check item->commit->object.flags to see
whether it was marked.

This interacts badly with --verbose, which will do a
separate walk to find the ahead/behind information for each
branch. There are two bad things that can happen:

  1. The ahead/behind walk may get the wrong results,
     because it can see a bogus UNINTERESTING flag leftover
     from the merge-filter walk.

  2. We may omit some branches if their tips are involved in
     the ahead/behind traversal of a branch shown earlier.
     The ahead/behind walk carefully cleans up its commit
     flags, meaning it may also erase the UNINTERESTING
     flag that we expect to check later.

We can solve this by moving the merge-filter state for each
ref into its "struct ref_item" as soon as we finish the
merge-filter walk. That fixes (2). Then we are free to clear
the commit flags we used in the walk, fixing (1).

Note that we actually do away with the matches_merge_filter
helper entirely here, and inline it between the revision
walk and the flag-clearing. This ensures that nobody
accidentally calls it at the wrong time (it is only safe to
check in that instant between the setting and clearing of
the global flag).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 29 insertions, 0 deletions

diff --git a/t/t3201-branch-contains.sh b/t/t3201-branch-contains.sh
index 141b0611e..912a6635a 100755
--- a/t/t3201-branch-contains.sh
+++ b/t/t3201-branch-contains.sh
@@ -130,4 +130,33 @@ test_expect_success 'implicit --list conflicts with modification options' '
 
 '
 
+# We want to set up a case where the walk for the tracking info
+# of one branch crosses the tip of another branch (and make sure
+# that the latter walk does not mess up our flag to see if it was
+# merged).
+#
+# Here "topic" tracks "master" with one extra commit, and "zzz" points to the
+# same tip as master The name "zzz" must come alphabetically after "topic"
+# as we process them in that order.
+test_expect_success 'branch --merged with --verbose' '
+	git branch --track topic master &&
+	git branch zzz topic &&
+	git checkout topic &&
+	test_commit foo &&
+	git branch --merged topic >actual &&
+	cat >expect <<-\EOF &&
+	  master
+	* topic
+	  zzz
+	EOF
+	test_cmp expect actual &&
+	git branch --verbose --merged topic >actual &&
+	cat >expect <<-\EOF &&
+	  master c77a0a9 second on master
+	* topic  2c939f4 [ahead 1] foo
+	  zzz    c77a0a9 second on master
+	EOF
+	test_cmp expect actual
+'
+
 test_done