Merge branch 'jk/pack-objects-with-bitmap-fix'

Hotfix of the base topic.

* jk/pack-objects-with-bitmap-fix:
  pack-bitmap: drop "loaded" flag
  traverse_bitmap_commit_list(): don't free result
  t5310: test delta reuse with bitmaps
  bitmap_has_sha1_in_uninteresting(): drop BUG check

pack-bitmap.c

@@ -91,8 +91,6 @@ struct bitmap_index {
 
 	/* Version of the bitmap index */
 	unsigned int version;
-
-	unsigned loaded : 1;
 };
 
 static struct ewah_bitmap *lookup_stored_bitmap(struct stored_bitmap *st)
@@ -306,7 +304,7 @@ static int open_pack_bitmap_1(struct bitmap_index *bitmap_git, struct packed_git
 
 static int load_pack_bitmap(struct bitmap_index *bitmap_git)
 {
-	assert(bitmap_git->map && !bitmap_git->loaded);
+	assert(bitmap_git->map);
 
 	bitmap_git->bitmaps = kh_init_sha1();
 	bitmap_git->ext_index.positions = kh_init_sha1_pos();
@@ -321,7 +319,6 @@ static int load_pack_bitmap(struct bitmap_index *bitmap_git)
 	if (load_bitmap_entries_v1(bitmap_git) < 0)
 		goto failed;
 
-	bitmap_git->loaded = 1;
 	return 0;
 
 failed:
@@ -336,7 +333,7 @@ static int open_pack_bitmap(struct bitmap_index *bitmap_git)
 	struct packed_git *p;
 	int ret = -1;
 
-	assert(!bitmap_git->map && !bitmap_git->loaded);
+	assert(!bitmap_git->map);
 
 	for (p = get_all_packs(the_repository); p; p = p->next) {
 		if (open_pack_bitmap_1(bitmap_git, p) == 0)
@@ -738,7 +735,7 @@ struct bitmap_index *prepare_bitmap_walk(struct rev_info *revs)
 	 * from disk. this is the point of no return; after this the rev_list
 	 * becomes invalidated and we must perform the revwalk through bitmaps
 	 */
-	if (!bitmap_git->loaded && load_pack_bitmap(bitmap_git) < 0)
+	if (load_pack_bitmap(bitmap_git) < 0)
 		goto cleanup;
 
 	object_array_clear(&revs->pending);
@@ -848,9 +845,6 @@ void traverse_bitmap_commit_list(struct bitmap_index *bitmap_git,
 		OBJ_TAG, show_reachable);
 
 	show_extended_objects(bitmap_git, show_reachable);
-
-	bitmap_free(bitmap_git->result);
-	bitmap_git->result = NULL;
 }
 
 static uint32_t count_object_type(struct bitmap_index *bitmap_git,
@@ -1128,8 +1122,6 @@ int bitmap_has_sha1_in_uninteresting(struct bitmap_index *bitmap_git,
 
 	if (!bitmap_git)
 		return 0; /* no bitmap loaded */
-	if (!bitmap_git->result)
-		BUG("failed to perform bitmap walk before querying");
 	if (!bitmap_git->haves)
 		return 0; /* walk had no "haves" */
 

pack-bitmap.h

@@ -54,7 +54,7 @@ int rebuild_existing_bitmaps(struct bitmap_index *, struct packing_data *mapping
 void free_bitmap_index(struct bitmap_index *);
 
 /*
- * After a traversal has been performed on the bitmap_index, this can be
+ * After a traversal has been performed by prepare_bitmap_walk(), this can be
  * queried to see if a particular object was reachable from any of the
  * objects flagged as UNINTERESTING.
  */

t/t5310-pack-bitmaps.sh

@@ -342,4 +342,97 @@ test_expect_success 'truncated bitmap fails gracefully' '
 	test_i18ngrep corrupt stderr
 '
 
+# have_delta <obj> <expected_base>
+#
+# Note that because this relies on cat-file, it might find _any_ copy of an
+# object in the repository. The caller is responsible for making sure
+# there's only one (e.g., via "repack -ad", or having just fetched a copy).
+have_delta () {
+	echo $2 >expect &&
+	echo $1 | git cat-file --batch-check="%(deltabase)" >actual &&
+	test_cmp expect actual
+}
+
+# Create a state of history with these properties:
+#
+#  - refs that allow a client to fetch some new history, while sharing some old
+#    history with the server; we use branches delta-reuse-old and
+#    delta-reuse-new here
+#
+#  - the new history contains an object that is stored on the server as a delta
+#    against a base that is in the old history
+#
+#  - the base object is not immediately reachable from the tip of the old
+#    history; finding it would involve digging down through history we know the
+#    other side has
+#
+# This should result in a state where fetching from old->new would not
+# traditionally reuse the on-disk delta (because we'd have to dig to realize
+# that the client has it), but we will do so if bitmaps can tell us cheaply
+# that the other side has it.
+test_expect_success 'set up thin delta-reuse parent' '
+	# This first commit contains the buried base object.
+	test-tool genrandom delta 16384 >file &&
+	git add file &&
+	git commit -m "delta base" &&
+	base=$(git rev-parse --verify HEAD:file) &&
+
+	# These intermediate commits bury the base back in history.
+	# This becomes the "old" state.
+	for i in 1 2 3 4 5
+	do
+		echo $i >file &&
+		git commit -am "intermediate $i" || return 1
+	done &&
+	git branch delta-reuse-old &&
+
+	# And now our new history has a delta against the buried base. Note
+	# that this must be smaller than the original file, since pack-objects
+	# prefers to create deltas from smaller objects to larger.
+	test-tool genrandom delta 16300 >file &&
+	git commit -am "delta result" &&
+	delta=$(git rev-parse --verify HEAD:file) &&
+	git branch delta-reuse-new &&
+
+	# Repack with bitmaps and double check that we have the expected delta
+	# relationship.
+	git repack -adb &&
+	have_delta $delta $base
+'
+
+# Now we can sanity-check the non-bitmap behavior (that the server is not able
+# to reuse the delta). This isn't strictly something we care about, so this
+# test could be scrapped in the future. But it makes sure that the next test is
+# actually triggering the feature we want.
+#
+# Note that our tools for working with on-the-wire "thin" packs are limited. So
+# we actually perform the fetch, retain the resulting pack, and inspect the
+# result.
+test_expect_success 'fetch without bitmaps ignores delta against old base' '
+	test_config pack.usebitmaps false &&
+	test_when_finished "rm -rf client.git" &&
+	git init --bare client.git &&
+	(
+		cd client.git &&
+		git config transfer.unpackLimit 1 &&
+		git fetch .. delta-reuse-old:delta-reuse-old &&
+		git fetch .. delta-reuse-new:delta-reuse-new &&
+		have_delta $delta $ZERO_OID
+	)
+'
+
+# And do the same for the bitmap case, where we do expect to find the delta.
+test_expect_success 'fetch with bitmaps can reuse old base' '
+	test_config pack.usebitmaps true &&
+	test_when_finished "rm -rf client.git" &&
+	git init --bare client.git &&
+	(
+		cd client.git &&
+		git config transfer.unpackLimit 1 &&
+		git fetch .. delta-reuse-old:delta-reuse-old &&
+		git fetch .. delta-reuse-new:delta-reuse-new &&
+		have_delta $delta $base
+	)
+'
+
 test_done