'Cancel' for PromiseKit

Cartfile

@@ -1,2 +1,4 @@
-github "mxcl/PromiseKit" ~> 6.0
+#github "mxcl/PromiseKit" ~> 6.0
+github "dougzilla32/PromiseKit" "CoreCancel"
+
 github "BoltsFramework/Bolts-ObjC" ~> 1.9

Cartfile.resolved

@@ -1,2 +1,2 @@
 github "BoltsFramework/Bolts-ObjC" "1.9.0"
-github "mxcl/PromiseKit" "6.3.3"
+github "dougzilla32/PromiseKit" "087b3cf470890ff9ea841212e2f3e285fecf3988"

Sources/BFTask+Promise.swift

@@ -9,8 +9,9 @@ extension Promise {
      */
     public func then<U>(on q: DispatchQueue? = conf.Q.map, body: @escaping (T) -> BFTask<U>) -> Promise<U?> {
         return then(on: q) { tee -> Promise<U?> in
+            let tokenSource = BFCancellationTokenSource()
             let task = body(tee)
-            return Promise<U?> { seal in
+            return Promise<U?>(cancellableTask: tokenSource) { seal in
                 task.continueWith(block: { task in
                     if task.isCompleted {
                         seal.fulfill(task.result)
@@ -20,8 +21,24 @@ extension Promise {
                         seal.reject(PMKError.invalidCallingConvention)
                     }
                     return nil
-                })
+                }, cancellationToken: tokenSource.token)
             }
         }
     }
 }
+
+/// Extend BFCancellationTokenSource to be a CancellableTask
+extension BFCancellationTokenSource: CancellableTask {
+    public var isCancelled: Bool {
+        return token.isCancellationRequested
+    }
+}
+
+extension CancellablePromise {
+    /**
+     The provided closure is executed when this cancellable promise is resolved.
+     */
+    public func then<U>(on q: DispatchQueue? = conf.Q.map, body: @escaping (T) -> BFTask<U>) -> CancellablePromise<U?> {
+        return cancellable(promise.then(on: q, body: body), cancelContext: self.cancelContext)
+    }
+}

Tests/TestBolts.swift

@@ -21,3 +21,31 @@ class TestBolts: XCTestCase {
         waitForExpectations(timeout: 1)
     }
 }
+
+//////////////////////////////////////////////////////////// Cancellation
+
+extension TestBolts {
+    func testCancel() {
+        let ex = expectation(description: "")
+
+        let value = { NSString(string: "1") }
+        var task: BFTask<NSString>?
+
+        let p = firstly { () -> CancellablePromise<Void> in
+            return CancellablePromise()
+        }
+        p.then { _ -> BFTask<NSString> in
+            task = BFTask(result: value())
+            p.cancel()
+            return task!
+        }.done { obj in
+            XCTAssertEqual(obj, value())
+            XCTFail()
+        }.catch(policy: .allErrors) {
+            $0.isCancelled ? ex.fulfill() : XCTFail()
+        }
+
+        waitForExpectations(timeout: 1)
+    }
+}
+