SI-8675 Add another test case for swallowed type errors

As reported on scala-internals. After tightening up the treatment
of undetermined type parameters in SI-7944, the enclosed test
case no longer typechecks. And since the regression fixed in the
previous commit, the error was swallowed by the typechecker only
to be burped up by a crash in the backend.

1 files changed, 22 insertions, 0 deletions

diff --git a/test/files/neg/t8675b.scala b/test/files/neg/t8675b.scala
new file mode 100644
index 0000000000..2c5015b1d0
--- /dev/null
+++ b/test/files/neg/t8675b.scala
@@ -0,0 +1,22 @@
+object Test {
+  trait Engine1
+
+  implicit class EngineTools1[Params, R](e: Engine1) {
+    def asRequirement: Requirement1[Params, R] = ???
+  }
+  trait Requirement1[Params, R] {
+    def pathsIncludingSelf: Traversable[List[Reportable1[Params, R]]]
+  }
+  trait Reportable1[Params, R]
+
+  // "missing paramater type" error was swallowed in 2.11.0 leading to a crash
+  // in the backend.
+  //
+  // This error is itself a regression (or at least a change) in 2.11.0-M7,
+  // specifically in SI-7944. The type paramaters to the implicit view
+  // `EngineTools1` are undetermined, and are now treated as type variables
+  // in the expected type of the closure argument to `withFilter`.
+  for (path: List[Any] <- (null : Engine1).asRequirement.pathsIncludingSelf.toList) {
+    ???
+  }
+}