Fix lost exception from dispatched withContext on cancelled job

Fixes #675

Author: elizarov

common/kotlinx-coroutines-core-common/src/Builders.common.kt

@@ -214,7 +214,7 @@ public suspend fun <T> withContext(
         }
     }
     // SLOW PATH -- use new dispatcher
-    val coroutine = DispatchedCoroutine(newContext, uCont) // MODE_DISPATCHED
+    val coroutine = DispatchedCoroutine(newContext, uCont) // MODE_ATOMIC_DEFAULT
     coroutine.initParentJob()
     block.startCoroutineCancellable(coroutine, coroutine)
     coroutine.getResult()
@@ -292,7 +292,7 @@ private class DispatchedCoroutine<in T>(
     context: CoroutineContext,
     uCont: Continuation<T>
 ) : ScopeCoroutine<T>(context, uCont) {
-    override val defaultResumeMode: Int get() = MODE_CANCELLABLE
+    override val defaultResumeMode: Int get() = MODE_ATOMIC_DEFAULT
 
     // this is copy-and-paste of a decision state machine inside AbstractionContinuation
     // todo: we may some-how abstract it via inline class

common/kotlinx-coroutines-core-common/test/CoroutineScopeTest.kt

@@ -219,6 +219,30 @@ class CoroutineScopeTest : TestBase() {
         }
     }
 
+    @Test
+    fun testCoroutineScopeCancellationVsException() = runTest {
+        expect(1)
+        var job: Job? = null
+        job = launch(start = CoroutineStart.UNDISPATCHED) {
+            expect(2)
+            try {
+                coroutineScope {
+                    expect(3)
+                    yield() // must suspend
+                    expect(5)
+                    job!!.cancel() // cancel this job _before_ it throws
+                    throw TestException1()
+                }
+            } catch (e: TestException1) {
+                // must have caught TextException
+                expect(6)
+            }
+        }
+        expect(4)
+        yield() // to coroutineScope
+        finish(7)
+    }
+
     @Test
     fun testScopePlusContext() {
         assertSame(EmptyCoroutineContext, scopePlusContext(EmptyCoroutineContext, EmptyCoroutineContext))

common/kotlinx-coroutines-core-common/test/SupervisorTest.kt

@@ -195,6 +195,30 @@ class SupervisorTest : TestBase() {
         assertTrue(parent.isCancelled)
     }
 
+    @Test
+    fun testSupervisorScopeCancellationVsException() = runTest {
+        expect(1)
+        var job: Job? = null
+        job = launch(start = CoroutineStart.UNDISPATCHED) {
+            expect(2)
+            try {
+                supervisorScope {
+                    expect(3)
+                    yield() // must suspend
+                    expect(5)
+                    job!!.cancel() // cancel this job _before_ it throws
+                    throw TestException1()
+                }
+            } catch (e: TestException1) {
+                // must have caught TextException
+                expect(6)
+            }
+        }
+        expect(4)
+        yield() // to coroutineScope
+        finish(7)
+    }
+
     private class TestException1 : Exception()
     private class TestException2 : Exception()
 }

common/kotlinx-coroutines-core-common/test/WithContextTest.kt

@@ -139,6 +139,60 @@ class WithContextTest : TestBase() {
         }
     }
 
+    @Test
+    fun testRunCancellationUndispatchedVsException() = runTest {
+        expect(1)
+        var job: Job? = null
+        job = launch(start = CoroutineStart.UNDISPATCHED) {
+            expect(2)
+            try {
+                // Same dispatcher, different context
+                withContext(CoroutineName("testRunCancellationUndispatchedVsException")) {
+                    expect(3)
+                    yield() // must suspend
+                    expect(5)
+                    job!!.cancel() // cancel this job _before_ it throws
+                    throw TestException()
+                }
+            } catch (e: TestException) {
+                // must have caught TextException
+                expect(6)
+            }
+        }
+        expect(4)
+        yield() // to coroutineScope
+        finish(7)
+    }
+
+    @Test
+    fun testRunCancellationDispatchedVsException() = runTest {
+        expect(1)
+        var job: Job? = null
+        job = launch(start = CoroutineStart.UNDISPATCHED) {
+            expect(2)
+            try {
+                // "Different" dispatcher (schedules execution back and forth)
+                withContext(wrapperDispatcher(coroutineContext)) {
+                    expect(4)
+                    yield() // must suspend
+                    expect(6)
+                    job!!.cancel() // cancel this job _before_ it throws
+                    throw TestException()
+                }
+            } catch (e: TestException) {
+                // must have caught TextException
+                expect(8)
+            }
+        }
+        expect(3)
+        yield() // withContext is next
+        expect(5)
+        yield() // withContext again
+        expect(7)
+        yield() // to catch block
+        finish(9)
+    }
+
     @Test
     fun testRunSelfCancellationWithException() = runTest(unhandled = listOf({e -> e is AssertionError})) {
         expect(1)