implementation for NSURLComponents.URLRelativeToURL API (#346)

remove semicolon

Author: mbvreddy

Foundation/NSURL.swift

@@ -647,7 +647,10 @@ public class NSURLComponents : NSObject, NSCopying {
 
     // Returns a URL created from the NSURLComponents relative to a base URL. If the NSURLComponents has an authority component (user, password, host or port) and a path component, then the path must either begin with "/" or be an empty string. If the NSURLComponents does not have an authority component (user, password, host or port) and has a path component, the path component must not start with "//". If those requirements are not met, nil is returned.
     public func URLRelativeToURL(_ baseURL: NSURL?) -> NSURL? {
-        NSUnimplemented()
+        if let componentString = string {
+            return NSURL(string: componentString, relativeToURL: baseURL)
+        }
+        return nil
     }
 
     // Returns a URL string created from the NSURLComponents. If the NSURLComponents has an authority component (user, password, host or port) and a path component, then the path must either begin with "/" or be an empty string. If the NSURLComponents does not have an authority component (user, password, host or port) and has a path component, the path component must not start with "//". If those requirements are not met, nil is returned.

TestFoundation/TestNSURL.swift

@@ -424,6 +424,7 @@ class TestNSURLComponents : XCTestCase {
         return [
             ("test_string", test_string),
             ("test_port", test_portSetter),
+            ("test_URLRelativeToURL", test_URLRelativeToURL),
         ]
     }
 
@@ -447,4 +448,46 @@ class TestNSURLComponents : XCTestCase {
         XCTAssertEqual(receivedString, expectedString, "expected \(expectedString) but received \(receivedString)")
     }
 
+    func test_URLRelativeToURL() {
+
+        let baseURL = NSURL(string: "https://www.example.com")
+
+        /* test NSURLComponents without authority */
+        let compWithAuthority = NSURLComponents(string: "https://www.swift.org")
+        compWithAuthority!.path = "/path/to/file with space.html"
+        compWithAuthority!.query = "id=23&search=Foo Bar"
+        var expectedString = "https://www.swift.org/path/to/file%20with%20space.html?id=23&search=Foo%20Bar"
+        XCTAssertEqual(compWithAuthority!.string, expectedString, "expected \(expectedString) but received \(compWithAuthority!.string)")
+
+        var url = compWithAuthority!.URLRelativeToURL(baseURL)
+        XCTAssertNotNil(url)
+        XCTAssertNil(url!.baseURL)
+        XCTAssertEqual(url!.absoluteString, expectedString, "expected \(expectedString) but received \(url!.absoluteString)")
+
+        compWithAuthority!.path = "path/to/file with space.html" //must start with /
+        XCTAssertNil(compWithAuthority!.string) // must be nil
+
+        url = compWithAuthority!.URLRelativeToURL(baseURL)
+        XCTAssertNil(url) //must be nil
+
+
+
+        /* test NSURLComponents without authority */
+        let compWithoutAuthority = NSURLComponents()
+        compWithoutAuthority.path = "path/to/file with space.html"
+        compWithoutAuthority.query = "id=23&search=Foo Bar"
+        expectedString = "path/to/file%20with%20space.html?id=23&search=Foo%20Bar"
+        XCTAssertEqual(compWithoutAuthority.string, expectedString, "expected \(expectedString) but received \(compWithoutAuthority.string)")
+
+        url = compWithoutAuthority.URLRelativeToURL(baseURL)
+        XCTAssertNotNil(url)
+        expectedString = "https://www.example.com/path/to/file%20with%20space.html?id=23&search=Foo%20Bar"
+        XCTAssertEqual(url!.absoluteString, expectedString, "expected \(expectedString) but received \(url!.absoluteString)")
+
+        compWithoutAuthority.path = "//path/to/file with space.html" //shouldn't start with //
+        XCTAssertNil(compWithoutAuthority.string) // must be nil
+
+        url = compWithoutAuthority.URLRelativeToURL(baseURL)
+        XCTAssertNil(url) //must be nil
+    }
 }