Fix inmemory driver find traversing too deep into directory nodes (#4996)

registry/storage/driver/inmemory/mfs.go

@@ -77,7 +77,7 @@ func (d *dir) find(q string) node {
 		return d
 	}
 
-	if child.isdir() {
+	if child.isdir() && i >= 0 {
 		// traverse down!
 		q = q[i+1:]
 		return child.(*dir).find(q)

registry/storage/driver/inmemory/mfs_test.go

@@ -0,0 +1,46 @@
+package inmemory
+
+import (
+	"testing"
+	"time"
+)
+
+// TestFindSameNamedChild checks that find returns a directory itself, not its
+// same-named child.
+func TestFindSameNamedChild(t *testing.T) {
+	root := &dir{common: common{p: "/", mod: time.Now()}}
+
+	if _, err := root.mkdirs("/dirname/dirname"); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := root.mkfile("/dirname/file"); err != nil {
+		t.Fatal(err)
+	}
+
+	for _, tc := range []struct {
+		query string
+		path  string
+		isdir bool
+	}{
+		{"/dirname", "/dirname", true},
+		{"dirname", "/dirname", true},
+		{"/dirname/", "/dirname", true},
+		{"/dirname/dirname", "/dirname/dirname", true},
+		{"/dirname/file", "/dirname/file", false},
+
+		// not found, so the closest existing parent is returned
+		{"/dirname/dirname/dirname", "/dirname/dirname", true},
+		{"/dirname/missing", "/dirname", true},
+		{"/missing", "/", true},
+	} {
+		t.Run(tc.query, func(t *testing.T) {
+			n := root.find(tc.query)
+			if n.path() != tc.path {
+				t.Errorf("find(%q).path() = %q, want %q", tc.query, n.path(), tc.path)
+			}
+			if n.isdir() != tc.isdir {
+				t.Errorf("find(%q).isdir() = %v, want %v", tc.query, n.isdir(), tc.isdir)
+			}
+		})
+	}
+}