Report non-fatal Runnable failures on MainThread EC

core/jvm/src/main/scala/cats/effect/IOApp.scala

@@ -568,12 +568,7 @@ trait IOApp {
               r.run()
             } catch {
               case t if NonFatal(t) =>
-                if (isForked) {
-                  t.printStackTrace()
-                  System.exit(1)
-                } else {
-                  throw t
-                }
+                IOApp.this.reportFailure(t).unsafeRunAndForgetWithoutCallback()(runtime)
 
               case t: Throwable =>
                 t.printStackTrace()

ioapp-tests/src/test/scala/IOAppSpec.scala

@@ -354,6 +354,11 @@ class IOAppSpec extends Specification {
         h.awaitStatus() mustEqual 0
       }
 
+      "use configurable reportFailure for runnables on MainThread" in {
+        val h = platform("MainThreadReportFailureRunnable", List.empty)
+        h.awaitStatus() mustEqual 0
+      }
+
       "warn on blocked threads" in {
         val h = platform("BlockedThreads", List.empty)
         h.awaitStatus()

tests/jvm/src/main/scala/catseffect/examplesplatform.scala

@@ -71,6 +71,19 @@ package examples {
 
   }
 
+  object MainThreadReportFailureRunnable extends IOApp {
+
+    val exitCode = new AtomicReference[ExitCode](ExitCode.Error)
+
+    override def reportFailure(err: Throwable): IO[Unit] =
+      IO(exitCode.set(ExitCode.Success))
+
+    def run(args: List[String]): IO[ExitCode] =
+      IO(MainThread.execute(() => throw new Exception)) *>
+        IO.sleep(1.second) *> IO(exitCode.get)
+
+  }
+
   object BlockedThreads extends IOApp.Simple {
 
     override protected def blockedThreadDetectionEnabled = true