Merge branch 'tb/pseudo-merge-bitmap-fixes'

We created a useless pseudo-merge reachability bitmap that is about
0 commits, and attempted to include commits that are not in packs,
which made no sense.  These bugs have been corrected.

* tb/pseudo-merge-bitmap-fixes:
  pseudo-merge.c: ensure pseudo-merge groups are closed
  pseudo-merge.c: do not generate empty pseudo-merge commits
  t/t5333-pseudo-merge-bitmaps.sh: demonstrate empty pseudo-merge groups
  pack-bitmap-write.c: select pseudo-merges even for small bitmaps
  pack-bitmap: drop redundant args from `bitmap_writer_finish()`
  pack-bitmap: drop redundant args from `bitmap_writer_build()`
  pack-bitmap: drop redundant args from `bitmap_writer_build_type_index()`
  pack-bitmap: initialize `bitmap_writer_init()` with packing_data

t/t5333-pseudo-merge-bitmaps.sh

@@ -390,4 +390,60 @@ test_expect_success 'pseudo-merge reuse' '
 	)
 '
 
+test_expect_success 'empty pseudo-merge group' '
+	git init pseudo-merge-empty-group &&
+	(
+		cd pseudo-merge-empty-group &&
+
+		# Ensure that a pseudo-merge group with no unstable
+		# commits does not generate an empty pseudo-merge
+		# bitmap.
+		git config bitmapPseudoMerge.empty.pattern refs/ &&
+
+		test_commit base &&
+		git repack -adb &&
+
+		test-tool bitmap dump-pseudo-merges >merges &&
+		test_line_count = 1 merges &&
+
+		test 0 -eq "$(grep -c commits=0 <merges)"
+	)
+'
+
+test_expect_success 'pseudo-merge closure' '
+	git init pseudo-merge-closure &&
+	(
+		cd pseudo-merge-closure &&
+
+		test_commit A &&
+		git repack -d &&
+
+		test_commit B &&
+
+		# Note that the contents of A is packed, but B is not. A
+		# (and the objects reachable from it) are thus visible
+		# to the MIDX, but the same is not true for B and its
+		# objects.
+		#
+		# Ensure that we do not attempt to create a pseudo-merge
+		# for B, depsite it matching the below pseudo-merge
+		# group pattern, as doing so would result in a failure
+		# to write a non-closed bitmap.
+		git config bitmapPseudoMerge.test.pattern refs/ &&
+		git config bitmapPseudoMerge.test.threshold now &&
+
+		git multi-pack-index write --bitmap &&
+
+		test-tool bitmap dump-pseudo-merges >pseudo-merges &&
+		test_line_count = 1 pseudo-merges &&
+
+		git rev-parse A >expect &&
+
+		test-tool bitmap list-commits >actual &&
+		test_cmp expect actual &&
+		test-tool bitmap dump-pseudo-merge-commits 0 >actual &&
+		test_cmp expect actual
+	)
+'
+
 test_done