Add .isAncestor(of:) method to URL

CotEditor/Sources/URL.swift

@@ -72,6 +72,20 @@ extension URL {
 
         self.components(relativeTo: baseURL).joined(separator: "/")
     }
+
+
+    /// Checks the given URL is ancestor of the receiver.
+    ///
+    /// - Parameter url: The child candidate URL.
+    /// - Returns: `true` if the given URL is child.
+    func isAncestor(of url: URL) -> Bool {
+
+        let ancestorComponents = self.standardizedFileURL.resolvingSymlinksInPath().pathComponents
+        let childComponents = url.standardizedFileURL.resolvingSymlinksInPath().pathComponents
+
+        return ancestorComponents.count < childComponents.count
+            && !zip(ancestorComponents, childComponents).contains(where: !=)
+    }
 }
 
 

Tests/URLExtensionsTests.swift

@@ -71,6 +71,17 @@ struct URLExtensionsTests {
     }
 
 
+    @Test func ancestor() throws {
+
+        let leaf = URL(fileURLWithPath: "/Dog/Cow/Cat")
+        let parent = leaf.deletingLastPathComponent()
+
+        #expect(parent.isAncestor(of: leaf))
+        #expect(!parent.isAncestor(of: URL(fileURLWithPath: "/Dog/Cow 1/Cat")))
+        #expect(!leaf.isAncestor(of: leaf))
+    }
+
+
     @Test func createItemReplacementDirectory() throws {
 
         #expect(throws: Never.self) { try URL.itemReplacementDirectory }