fix(key): only count a key as an ancestor if there is a separator

key.go

@@ -212,20 +212,27 @@ func (k Key) ChildString(s string) Key {
 //   NewKey("/Comedy").IsAncestorOf("/Comedy/MontyPython")
 //   true
 func (k Key) IsAncestorOf(other Key) bool {
-	if other.string == k.string {
+	// equivalent to HasPrefix(other, k.string + "/")
+
+	if len(other.string) <= len(k.string) {
+		// We're not long enough to be a child.
 		return false
 	}
-	return strings.HasPrefix(other.string, k.string)
+
+	if k.string == "/" {
+		// We're the root and the other key is longer.
+		return true
+	}
+
+	// "other" starts with /k.string/
+	return other.string[len(k.string)] == '/' && other.string[:len(k.string)] == k.string
 }
 
 // IsDescendantOf returns whether this key contains another as a prefix.
 //   NewKey("/Comedy/MontyPython").IsDescendantOf("/Comedy")
 //   true
 func (k Key) IsDescendantOf(other Key) bool {
-	if other.string == k.string {
-		return false
-	}
-	return strings.HasPrefix(k.string, other.string)
+	return other.IsAncestorOf(k)
 }
 
 // IsTopLevel returns whether this key has only one namespace.

key_test.go

@@ -84,19 +84,23 @@ func CheckTrue(c *C, cond bool) {
 func (ks *KeySuite) TestKeyAncestry(c *C) {
 	k1 := NewKey("/A/B/C")
 	k2 := NewKey("/A/B/C/D")
+	k3 := NewKey("/AB")
+	k4 := NewKey("/A")
 
 	c.Check(k1.String(), Equals, "/A/B/C")
 	c.Check(k2.String(), Equals, "/A/B/C/D")
 	CheckTrue(c, k1.IsAncestorOf(k2))
 	CheckTrue(c, k2.IsDescendantOf(k1))
-	CheckTrue(c, NewKey("/A").IsAncestorOf(k2))
-	CheckTrue(c, NewKey("/A").IsAncestorOf(k1))
-	CheckTrue(c, !NewKey("/A").IsDescendantOf(k2))
-	CheckTrue(c, !NewKey("/A").IsDescendantOf(k1))
-	CheckTrue(c, k2.IsDescendantOf(NewKey("/A")))
-	CheckTrue(c, k1.IsDescendantOf(NewKey("/A")))
-	CheckTrue(c, !k2.IsAncestorOf(NewKey("/A")))
-	CheckTrue(c, !k1.IsAncestorOf(NewKey("/A")))
+	CheckTrue(c, k4.IsAncestorOf(k2))
+	CheckTrue(c, k4.IsAncestorOf(k1))
+	CheckTrue(c, !k4.IsDescendantOf(k2))
+	CheckTrue(c, !k4.IsDescendantOf(k1))
+	CheckTrue(c, !k3.IsDescendantOf(k4))
+	CheckTrue(c, !k4.IsAncestorOf(k3))
+	CheckTrue(c, k2.IsDescendantOf(k4))
+	CheckTrue(c, k1.IsDescendantOf(k4))
+	CheckTrue(c, !k2.IsAncestorOf(k4))
+	CheckTrue(c, !k1.IsAncestorOf(k4))
 	CheckTrue(c, !k2.IsAncestorOf(k2))
 	CheckTrue(c, !k1.IsAncestorOf(k1))
 	c.Check(k1.Child(NewKey("D")).String(), Equals, k2.String())