Merge branch 'jh/notes-fanout-fix' into maint

The code to automatically shrink the fan-out in the notes tree had
an off-by-one bug, which has been killed.

* jh/notes-fanout-fix:
  notes.c: fix off-by-one error when decreasing notes fanout
  t3305: check notes fanout more carefully and robustly

notes.c

@@ -576,16 +576,16 @@ redo:
 			 * the note tree that have not yet been explored. There
 			 * is a direct relationship between subtree entries at
 			 * level 'n' in the tree, and the 'fanout' variable:
-			 * Subtree entries at level 'n <= 2 * fanout' should be
+			 * Subtree entries at level 'n < 2 * fanout' should be
 			 * preserved, since they correspond exactly to a fanout
 			 * directory in the on-disk structure. However, subtree
-			 * entries at level 'n > 2 * fanout' should NOT be
+			 * entries at level 'n >= 2 * fanout' should NOT be
 			 * preserved, but rather consolidated into the above
 			 * notes tree level. We achieve this by unconditionally
 			 * unpacking subtree entries that exist below the
 			 * threshold level at 'n = 2 * fanout'.
 			 */
-			if (n <= 2 * fanout &&
+			if (n < 2 * fanout &&
 			    flags & FOR_EACH_NOTE_YIELD_SUBTREES) {
 				/* invoke callback with subtree */
 				unsigned int path_len =
@@ -602,7 +602,7 @@ redo:
 					 path,
 					 cb_data);
 			}
-			if (n > fanout * 2 ||
+			if (n >= 2 * fanout ||
 			    !(flags & FOR_EACH_NOTE_DONT_UNPACK_SUBTREES)) {
 				/* unpack subtree and resume traversal */
 				tree->a[i] = NULL;
@@ -723,13 +723,15 @@ static int write_each_note_helper(struct tree_write_stack *tws,
 
 struct write_each_note_data {
 	struct tree_write_stack *root;
-	struct non_note *next_non_note;
+	struct non_note **nn_list;
+	struct non_note *nn_prev;
 };
 
 static int write_each_non_note_until(const char *note_path,
 		struct write_each_note_data *d)
 {
-	struct non_note *n = d->next_non_note;
+	struct non_note *p = d->nn_prev;
+	struct non_note *n = p ? p->next : *d->nn_list;
 	int cmp = 0, ret;
 	while (n && (!note_path || (cmp = strcmp(n->path, note_path)) <= 0)) {
 		if (note_path && cmp == 0)
@@ -740,9 +742,10 @@ static int write_each_non_note_until(const char *note_path,
 			if (ret)
 				return ret;
 		}
+		p = n;
 		n = n->next;
 	}
-	d->next_non_note = n;
+	d->nn_prev = p;
 	return 0;
 }
 
@@ -1177,7 +1180,8 @@ int write_notes_tree(struct notes_tree *t, struct object_id *result)
 	strbuf_init(&root.buf, 256 * (32 + the_hash_algo->hexsz)); /* assume 256 entries */
 	root.path[0] = root.path[1] = '\0';
 	cb_data.root = &root;
-	cb_data.next_non_note = t->first_non_note;
+	cb_data.nn_list = &(t->first_non_note);
+	cb_data.nn_prev = NULL;
 
 	/* Write tree objects representing current notes tree */
 	flags = FOR_EACH_NOTE_DONT_UNPACK_SUBTREES |

t/t3305-notes-fanout.sh

@@ -4,6 +4,38 @@ test_description='Test that adding/removing many notes triggers automatic fanout
 
 . ./test-lib.sh
 
+path_has_fanout() {
+	path=$1 &&
+	fanout=$2 &&
+	after_last_slash=$((40 - $fanout * 2)) &&
+	echo $path | grep -q "^\([0-9a-f]\{2\}/\)\{$fanout\}[0-9a-f]\{$after_last_slash\}$"
+}
+
+touched_one_note_with_fanout() {
+	notes_commit=$1 &&
+	modification=$2 &&  # 'A' for addition, 'D' for deletion
+	fanout=$3 &&
+	diff=$(git diff-tree --no-commit-id --name-status --root -r $notes_commit) &&
+	path=$(echo $diff | sed -e "s/^$modification[\t ]//") &&
+	path_has_fanout "$path" $fanout;
+}
+
+all_notes_have_fanout() {
+	notes_commit=$1 &&
+	fanout=$2 &&
+	git ls-tree -r --name-only $notes_commit 2>/dev/null |
+	while read path
+	do
+		path_has_fanout $path $fanout || return 1
+	done
+}
+
+test_expect_success 'tweak test environment' '
+	git checkout -b nondeterminism &&
+	test_commit A &&
+	git checkout --orphan with_notes;
+'
+
 test_expect_success 'creating many notes with git-notes' '
 	num_notes=300 &&
 	i=0 &&
@@ -20,7 +52,7 @@ test_expect_success 'creating many notes with git-notes' '
 
 test_expect_success 'many notes created correctly with git-notes' '
 	git log | grep "^    " > output &&
-	i=300 &&
+	i=$num_notes &&
 	while test $i -gt 0
 	do
 		echo "    commit #$i" &&
@@ -30,34 +62,46 @@ test_expect_success 'many notes created correctly with git-notes' '
 	test_cmp expect output
 '
 
-test_expect_success 'many notes created with git-notes triggers fanout' '
-	# Expect entire notes tree to have a fanout == 1
-	git ls-tree -r --name-only refs/notes/commits |
-	while read path
+test_expect_success 'stable fanout 0 is followed by stable fanout 1' '
+	i=$num_notes &&
+	fanout=0 &&
+	while test $i -gt 0
 	do
-		echo $path | grep "^../[0-9a-f]*$" || {
-			echo "Invalid path \"$path\"" &&
-			return 1;
-		}
-	done
+		i=$(($i - 1)) &&
+		if touched_one_note_with_fanout refs/notes/commits~$i A $fanout
+		then
+			continue
+		elif test $fanout -eq 0
+		then
+			fanout=1 &&
+			if all_notes_have_fanout refs/notes/commits~$i $fanout
+			then
+				echo "Fanout 0 -> 1 at refs/notes/commits~$i" &&
+				continue
+			fi
+		fi &&
+		echo "Failed fanout=$fanout check at refs/notes/commits~$i" &&
+		git ls-tree -r --name-only refs/notes/commits~$i &&
+		return 1
+	done &&
+	all_notes_have_fanout refs/notes/commits 1
 '
 
 test_expect_success 'deleting most notes with git-notes' '
-	num_notes=250 &&
+	remove_notes=285 &&
 	i=0 &&
 	git rev-list HEAD |
-	while test $i -lt $num_notes && read sha1
+	while test $i -lt $remove_notes && read sha1
 	do
 		i=$(($i + 1)) &&
 		test_tick &&
-		git notes remove "$sha1" ||
-		exit 1
+		git notes remove "$sha1" 2>/dev/null || return 1
 	done
 '
 
 test_expect_success 'most notes deleted correctly with git-notes' '
-	git log HEAD~250 | grep "^    " > output &&
-	i=50 &&
+	git log HEAD~$remove_notes | grep "^    " > output &&
+	i=$(($num_notes - $remove_notes)) &&
 	while test $i -gt 0
 	do
 		echo "    commit #$i" &&
@@ -67,16 +111,29 @@ test_expect_success 'most notes deleted correctly with git-notes' '
 	test_cmp expect output
 '
 
-test_expect_success 'deleting most notes triggers fanout consolidation' '
-	# Expect entire notes tree to have a fanout == 0
-	git ls-tree -r --name-only refs/notes/commits |
-	while read path
+test_expect_success 'stable fanout 1 is followed by stable fanout 0' '
+	i=$remove_notes &&
+	fanout=1 &&
+	while test $i -gt 0
 	do
-		echo $path | grep -v "^../.*" || {
-			echo "Invalid path \"$path\"" &&
-			return 1;
-		}
-	done
+		i=$(($i - 1)) &&
+		if touched_one_note_with_fanout refs/notes/commits~$i D $fanout
+		then
+			continue
+		elif test $fanout -eq 1
+		then
+			fanout=0 &&
+			if all_notes_have_fanout refs/notes/commits~$i $fanout
+			then
+				echo "Fanout 1 -> 0 at refs/notes/commits~$i" &&
+				continue
+			fi
+		fi &&
+		echo "Failed fanout=$fanout check at refs/notes/commits~$i" &&
+		git ls-tree -r --name-only refs/notes/commits~$i &&
+		return 1
+	done &&
+	all_notes_have_fanout refs/notes/commits 0
 '
 
 test_done