refs: fix loose-ref seeking across directory boundaries

When seeking through loose refs, cache_ref_iterator_seek() compares
each directory component without its trailing slash. This can confuse
a directory with a similarly named ref that sorts before it.

For example, with these refs:

    refs/tags/releases-z
    refs/tags/releases/v1
    refs/tags/releases/v2

Starting after refs/tags/releases/v1 can position the iterator at
releases-z instead of descending into releases/. Iteration then
returns v1 again, even though it should return only v2.

Include the trailing slash when comparing directory components so
that the seek follows the correct directory.

Also handle two related positioning errors. If every entry in a
directory precedes the cursor, stop searching that level rather than
descending into its last entry. If a leaf sorts after the cursor,
leave the iterator positioned to return it, even when the cursor has
remaining path components.

Add regression tests for shared-prefix names, missing nested markers,
and markers beyond the end of the ref listing, using loose, packed,
and mixed refs.

Signed-off-by: Venkat Ragavan S <mail2venkat21@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

refs/ref-cache.c

@@ -506,7 +506,7 @@ static int cache_ref_iterator_seek(struct ref_iterator *ref_iterator,
 			sort_ref_dir(dir);
 
 			slash = strchr(slash, '/');
-			len = slash ? (size_t)(slash - refname) : strlen(refname);
+			len = slash ? (size_t)(slash - refname + 1) : strlen(refname);
 
 			for (idx = 0; idx < dir->nr; idx++) {
 				cmp = strncmp(refname, dir->entries[idx]->name, len);
@@ -520,6 +520,8 @@ static int cache_ref_iterator_seek(struct ref_iterator *ref_iterator,
 				slash = slash + 1;
 
 			level->index = idx;
+			if (cmp > 0)
+				break;
 			if (dir->entries[idx]->flag & REF_DIR) {
 				/* push down a level */
 				dir = get_ref_dir(dir->entries[idx]);
@@ -532,7 +534,7 @@ static int cache_ref_iterator_seek(struct ref_iterator *ref_iterator,
 				level->prefix_state = PREFIX_CONTAINS_DIR;
 			} else {
 				/* reduce the index so the leaf node is iterated over */
-				if (cmp <= 0 && !slash)
+				if (cmp < 0 || (cmp == 0 && !slash))
 					level->index = idx - 1;
 				/*
 				 * while the seek path may not be exhausted, our

t/t6302-for-each-ref-filter.sh

@@ -746,6 +746,61 @@ test_expect_success 'start after used with a pattern' '
 	test_cmp expect actual
 '
 
+for storage in loose packed mixed
+do
+	test_expect_success "start after respects directory boundaries ($storage)" '
+		test_when_finished "rm -rf repo" &&
+		git init repo &&
+		(
+			cd repo &&
+			test_commit --no-tag base &&
+			git update-ref refs/tags/packed HEAD &&
+			if test "$storage" = mixed
+			then
+				git pack-refs --all || return 1
+			fi &&
+			git update-ref --stdin <<-\EOF &&
+			create refs/tags/a-leaf HEAD
+			create refs/tags/a/nested HEAD
+			create refs/tags/a0 HEAD
+			create refs/tags/b HEAD
+			create refs/tags/releases-z HEAD
+			create refs/tags/releases/v1 HEAD
+			create refs/tags/releases/v2 HEAD
+			EOF
+			if test "$storage" = packed
+			then
+				git pack-refs --all || return 1
+			fi &&
+			echo refs/tags/releases/v2 >expect &&
+			git for-each-ref --no-sort --format="%(refname)" \
+				--start-after=refs/tags/releases/v1 >actual &&
+			test_cmp expect actual &&
+			cat >expect <<-\EOF &&
+			refs/tags/a0
+			refs/tags/b
+			refs/tags/packed
+			refs/tags/releases-z
+			refs/tags/releases/v1
+			refs/tags/releases/v2
+			EOF
+			git for-each-ref --no-sort --format="%(refname)" \
+				--start-after=refs/tags/a/next >actual &&
+			test_cmp expect actual &&
+			tail -n 5 expect >expect-later &&
+			git for-each-ref --no-sort --format="%(refname)" \
+				--start-after=refs/tags/aa/missing >actual &&
+			test_cmp expect-later actual &&
+			for marker in refs/tags/zzzz refs/zzzz zzzz
+			do
+				git for-each-ref --no-sort --format="%(refname)" \
+					--start-after="$marker" >actual &&
+				test_must_be_empty actual || return 1
+			done
+		)
+	'
+done
+
 test_expect_success 'start after used with custom sort order' '
 	cat >expect <<-\EOF &&
 	fatal: cannot use --start-after with custom sort options