untracked cache: fix entry invalidation

First, the current code in untracked_cache_invalidate_path() is wrong
because it can only handle paths "a" or "a/b", not "a/b/c" because
lookup_untracked() only looks for entries directly under the given
directory. In the last case, it will look for the entry "b/c" in
directory "a" instead. This means if you delete or add an entry in a
subdirectory, untracked cache may become out of date because it does not
invalidate properly. This is noticed by David Turner.

The second problem is about invalidation inside a fully untracked/excluded
directory. In this case we may have to invalidate back to root. See the
comment block for detail.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

dir.c

@@ -2616,23 +2616,67 @@ done2:
 	return uc;
 }
 
+static void invalidate_one_directory(struct untracked_cache *uc,
+				     struct untracked_cache_dir *ucd)
+{
+	uc->dir_invalidated++;
+	ucd->valid = 0;
+	ucd->untracked_nr = 0;
+}
+
+/*
+ * Normally when an entry is added or removed from a directory,
+ * invalidating that directory is enough. No need to touch its
+ * ancestors. When a directory is shown as "foo/bar/" in git-status
+ * however, deleting or adding an entry may have cascading effect.
+ *
+ * Say the "foo/bar/file" has become untracked, we need to tell the
+ * untracked_cache_dir of "foo" that "bar/" is not an untracked
+ * directory any more (because "bar" is managed by foo as an untracked
+ * "file").
+ *
+ * Similarly, if "foo/bar/file" moves from untracked to tracked and it
+ * was the last untracked entry in the entire "foo", we should show
+ * "foo/" instead. Which means we have to invalidate past "bar" up to
+ * "foo".
+ *
+ * This function traverses all directories from root to leaf. If there
+ * is a chance of one of the above cases happening, we invalidate back
+ * to root. Otherwise we just invalidate the leaf. There may be a more
+ * sophisticated way than checking for SHOW_OTHER_DIRECTORIES to
+ * detect these cases and avoid unnecessary invalidation, for example,
+ * checking for the untracked entry named "bar/" in "foo", but for now
+ * stick to something safe and simple.
+ */
+static int invalidate_one_component(struct untracked_cache *uc,
+				    struct untracked_cache_dir *dir,
+				    const char *path, int len)
+{
+	const char *rest = strchr(path, '/');
+
+	if (rest) {
+		int component_len = rest - path;
+		struct untracked_cache_dir *d =
+			lookup_untracked(uc, dir, path, component_len);
+		int ret =
+			invalidate_one_component(uc, d, rest + 1,
+						 len - (component_len + 1));
+		if (ret)
+			invalidate_one_directory(uc, dir);
+		return ret;
+	}
+
+	invalidate_one_directory(uc, dir);
+	return uc->dir_flags & DIR_SHOW_OTHER_DIRECTORIES;
+}
+
 void untracked_cache_invalidate_path(struct index_state *istate,
 				     const char *path)
 {
-	const char *sep;
-	struct untracked_cache_dir *d;
 	if (!istate->untracked || !istate->untracked->root)
 		return;
-	sep = strrchr(path, '/');
-	if (sep)
-		d = lookup_untracked(istate->untracked,
-				     istate->untracked->root,
-				     path, sep - path);
-	else
-		d = istate->untracked->root;
-	istate->untracked->dir_invalidated++;
-	d->valid = 0;
-	d->untracked_nr = 0;
+	invalidate_one_component(istate->untracked, istate->untracked->root,
+				 path, strlen(path));
 }
 
 void untracked_cache_remove_from_index(struct index_state *istate,

t/t7063-status-untracked-cache.sh

@@ -375,7 +375,7 @@ EOF
 node creation: 0
 gitignore invalidation: 0
 directory invalidation: 0
-opendir: 1
+opendir: 2
 EOF
 	test_cmp ../trace.expect ../trace
 '
@@ -543,4 +543,30 @@ EOF
 	test_cmp ../trace.expect ../trace
 '
 
+test_expect_success 'move entry in subdir from untracked to cached' '
+	git add dtwo/two &&
+	git status --porcelain >../status.actual &&
+	cat >../status.expect <<EOF &&
+ M done/two
+A  dtwo/two
+?? .gitignore
+?? done/five
+?? done/sub/
+EOF
+	test_cmp ../status.expect ../status.actual
+'
+
+test_expect_success 'move entry in subdir from cached to untracked' '
+	git rm --cached dtwo/two &&
+	git status --porcelain >../status.actual &&
+	cat >../status.expect <<EOF &&
+ M done/two
+?? .gitignore
+?? done/five
+?? done/sub/
+?? dtwo/
+EOF
+	test_cmp ../status.expect ../status.actual
+'
+
 test_done