From 3fb01cbc177d6f8e3f1ecd1c208e0bb766ae2c49 Mon Sep 17 00:00:00 2001
From: Ruslan Shevchenko <ruslan@shevchenko.kiev.ua>
Date: Mon, 18 Nov 2024 19:54:03 +0200
Subject: [PATCH]  unwrap exceptions from CompletableFuture

---
 .../monads/CompletableFutureCpsMonad.scala    | 54 ++++++++++++++-----
 ...estAsyncExceptionInCompletableFuture.scala | 46 ++++++++++++++++
 2 files changed, 86 insertions(+), 14 deletions(-)
 create mode 100644 jvm/src/test/scala/cpstest/TestAsyncExceptionInCompletableFuture.scala

diff --git a/jvm/src/main/scala/cps/monads/CompletableFutureCpsMonad.scala b/jvm/src/main/scala/cps/monads/CompletableFutureCpsMonad.scala
index 02fd325a5..01e140397 100644
--- a/jvm/src/main/scala/cps/monads/CompletableFutureCpsMonad.scala
+++ b/jvm/src/main/scala/cps/monads/CompletableFutureCpsMonad.scala
@@ -1,10 +1,10 @@
 package cps.monads
 
-import cps._
-import java.util.concurrent.CompletableFuture
-import scala.util.Try
-import scala.util.Failure
-import scala.util.Success
+import cps.*
+
+import java.util.concurrent.{CompletableFuture, CompletionException}
+import scala.concurrent.Future
+import scala.util.{Failure, NotGiven, Success, Try}
 import scala.util.control.NonFatal
 
 
@@ -30,7 +30,7 @@ given CompletableFutureCpsMonad: CpsSchedulingMonad[CompletableFuture] with CpsT
             if (e == null) then
                f(Success(v.nn))
             else
-               f(Failure(e.nn))
+               f(Failure(unwrapCompletableException(e.nn)))
         }.nn.toCompletableFuture.nn
 
    override def flatMapTry[A,B](fa:CompletableFuture[A])(f: Try[A]=>CompletableFuture[B]):CompletableFuture[B] =
@@ -42,18 +42,18 @@ given CompletableFutureCpsMonad: CpsSchedulingMonad[CompletableFuture] with CpsT
                  if (e1 == null) then
                     retval.complete(v1.nn)
                  else
-                    retval.completeExceptionally(e1.nn)
+                    retval.completeExceptionally(unwrapCompletableException(e1))
               } 
             catch
               case NonFatal(ex) =>
-                 retval.completeExceptionally(ex)
+                 retval.completeExceptionally(unwrapCompletableException(ex))
           else
             try
-              f(Failure(e.nn)).handle{ (v1,e1) =>
+              f(Failure(unwrapCompletableException(e.nn))).handle{ (v1,e1) =>
                  if (e1 == null) then
                     retval.complete(v1.nn)
                  else
-                    retval.completeExceptionally(e1.nn)
+                    retval.completeExceptionally(unwrapCompletableException(e1.nn))
               }
             catch
               case NonFatal(ex) =>
@@ -69,11 +69,11 @@ given CompletableFutureCpsMonad: CpsSchedulingMonad[CompletableFuture] with CpsT
              retval.complete(v.nn)
           else
              try
-                fx(e).handle{ (v1,e1) =>
+                fx(unwrapCompletableException(e)).handle{ (v1,e1) =>
                    if (e1 == null) then
                       retval.complete(v1.nn)
                    else
-                      retval.completeExceptionally(e1.nn)
+                      retval.completeExceptionally(unwrapCompletableException(e1.nn))
                 }
              catch
                 case NonFatal(ex) =>
@@ -98,7 +98,7 @@ given CompletableFutureCpsMonad: CpsSchedulingMonad[CompletableFuture] with CpsT
               if (e == null)
                  r.complete(v)
               else
-                 r.completeExceptionally(e)
+                 r.completeExceptionally(unwrapCompletableException(e))
             }
           catch
             case NonFatal(e) =>
@@ -106,12 +106,38 @@ given CompletableFutureCpsMonad: CpsSchedulingMonad[CompletableFuture] with CpsT
         }
         r
 
-    def tryCancel[A](op: CompletableFuture[A]): CompletableFuture[Unit] =
+   def tryCancel[A](op: CompletableFuture[A]): CompletableFuture[Unit] =
         if (op.cancel(true)) then
            CompletableFuture.completedFuture(()).nn
         else
            CompletableFuture.failedFuture(new IllegalStateException("CompletableFuture is not cancelled")).nn
 
+
+   private def unwrapCompletableException(ex: Throwable): Throwable =
+        if (ex.isInstanceOf[CompletionException] && ex.getCause() != null) then
+           ex.getCause().nn
+        else
+           ex.nn
+
+
+   given fromCompletableFutureConversion[G[_], T](using CpsAsyncMonad[G], CpsMonadContext[G]): CpsMonadConversion[CompletableFuture, G] with
+
+    def apply[T](ft: CompletableFuture[T]): G[T] =
+      summon[CpsAsyncMonad[G]].adoptCallbackStyle(listener =>
+        val _unused = ft.whenComplete(
+          (v, e) =>
+            if (e == null) then
+              listener(Success(v))
+            else
+              if (e.isInstanceOf[CompletionException] && e.getCause() != null) then
+                listener(Failure(e.getCause()))
+              else
+                listener(Failure(e))
+        )
+      )
+
+
 }
 
 
+
diff --git a/jvm/src/test/scala/cpstest/TestAsyncExceptionInCompletableFuture.scala b/jvm/src/test/scala/cpstest/TestAsyncExceptionInCompletableFuture.scala
new file mode 100644
index 000000000..d39d896f0
--- /dev/null
+++ b/jvm/src/test/scala/cpstest/TestAsyncExceptionInCompletableFuture.scala
@@ -0,0 +1,46 @@
+package cpstest
+
+import org.junit.{Ignore, Test}
+import org.junit.Assert.*
+
+import java.util.concurrent.CompletableFuture
+import scala.concurrent.*
+import scala.concurrent.duration.*
+import scala.util.*
+import scala.util.control.*
+import scala.concurrent.ExecutionContext.Implicits.global
+
+import cps.*
+import cps.monads.{*, given}
+
+class TestAsyncExceptionInCompletableFuture {
+
+  object X {
+
+    def completableFutureMethod(): CompletableFuture[Int] = {
+      val cf = new CompletableFuture[Int]()
+      cf.completeExceptionally(new IllegalStateException("test exception"))
+      cf
+    }
+
+  }
+
+  @Test
+  def testExceptinInCompletableFuture(): Unit = {
+    val f = async[Future] {
+      try {
+        val x = X.completableFutureMethod().await
+        x
+      } catch {
+        case ex: IllegalStateException =>
+          -1
+        case NonFatal(ex) =>
+          println(s"unexpected exception: $ex")
+          throw ex
+      }
+    }
+    val x = Await.ready(f, 1.second)
+    assert(f.value.get.get == -1)
+  }
+
+}