From 00a1e6dfc08390493bbfe702333ff341a2e7172e Mon Sep 17 00:00:00 2001
From: Dmitry Karlinsky <dmitryka@wix.com>
Date: Sat, 11 Jan 2020 21:05:40 +0200
Subject: [PATCH] Adding test reproducing the compiler crash reported in #7965

---
 .../dotty/tools/dotc/CompilationTests.scala   |  7 ++++
 .../failureToJoinAlternatives.scala           | 38 +++++++++++++++++++
 2 files changed, 45 insertions(+)
 create mode 100644 tests/compiler-crash/failureToJoinAlternatives.scala

diff --git a/compiler/test/dotty/tools/dotc/CompilationTests.scala b/compiler/test/dotty/tools/dotc/CompilationTests.scala
index 8e5cf657a624..3ae09a5f3381 100644
--- a/compiler/test/dotty/tools/dotc/CompilationTests.scala
+++ b/compiler/test/dotty/tools/dotc/CompilationTests.scala
@@ -284,6 +284,13 @@ class CompilationTests extends ParallelTesting {
     implicit val testGroup: TestGroup = TestGroup("explicitNullsRun")
     compileFilesInDir("tests/explicit-nulls/run", explicitNullsOptions)
   }.checkRuns()
+
+  @Test def compilerCrash: Unit = {
+      implicit val testGroup: TestGroup = TestGroup("compilePos")
+      aggregateTests(
+        compileFilesInDir("tests/compiler-crash", defaultOptions),
+      )
+    }.checkCompile()
 }
 
 object CompilationTests {
diff --git a/tests/compiler-crash/failureToJoinAlternatives.scala b/tests/compiler-crash/failureToJoinAlternatives.scala
new file mode 100644
index 000000000000..aca7e5108512
--- /dev/null
+++ b/tests/compiler-crash/failureToJoinAlternatives.scala
@@ -0,0 +1,38 @@
+
+class Has[A]
+
+trait ZLayer[-RIn, +E, +ROut <: Has[_]] {
+  def >>>[E1 >: E, ROut2 <: Has[_]](that: ZLayer[ROut, E1, ROut2]): ZLayer[RIn, E1, ROut2]
+  def ++[E1 >: E, RIn2, ROut1 >: ROut <: Has[_], ROut2 <: Has[_]](that: ZLayer[RIn2, E1, ROut2]): ZLayer[RIn with RIn2, E1, ROut1 with ROut2]
+}
+object ZLayer {
+  type NoDeps[+E, +B <: Has[_]] = ZLayer[Any, E, B]
+}
+
+type ServiceA = Has[ServiceA.Service]
+object ServiceA {
+  trait Service
+  val live: ZLayer.NoDeps[Nothing, ServiceA] = ???
+}
+
+type ServiceB = Has[ServiceB.Service]
+object ServiceB {
+  trait Service
+  val live: ZLayer.NoDeps[Nothing, ServiceB] = ???
+}
+
+type ServiceC = Has[ServiceC.Service]
+object ServiceC {
+  trait Service
+  val live: ZLayer.NoDeps[Nothing, ServiceC] = ???
+}
+
+type ServiceD = Has[ServiceD.Service]
+object ServiceD {
+  trait Service
+  val live: ZLayer.NoDeps[ServiceC, ServiceD with ServiceC] = ???
+}
+
+val combined =
+    ServiceA.live >>>
+      (ServiceB.live ++ (ServiceC.live >>> ServiceD.live))