Fix for crasher during type inference.

Well, "fix" is pretty generous, how about "workaround".
It does seem to do the job.  Closes SI-4070, review by @moors.

1 files changed, 37 insertions, 0 deletions

diff --git a/test/files/pos/t4070.scala b/test/files/pos/t4070.scala
new file mode 100644
index 0000000000..29c8d16e30
--- /dev/null
+++ b/test/files/pos/t4070.scala
@@ -0,0 +1,37 @@
+package a {
+  // method before classes
+  trait Foo {
+    def crash(x: Dingus[_]): Unit = x match { case m: Bippy[tv] => () }
+
+    class Dingus[T]
+    class Bippy[CC[X] <: Seq[X]]() extends Dingus[CC[Int]]
+  }
+}
+
+package b {
+  // classes before method
+  trait Foo {
+    class Dingus[T]
+    class Bippy[CC[X] <: Seq[X]]() extends Dingus[CC[Int]]
+
+    def crash(x: Dingus[_]): Unit = x match { case m: Bippy[tv] => () }
+  }
+}
+
+
+/*
+// With crash below the clasess:
+% scalac -Dscalac.debug.tvar ./a.scala 
+[    create] ?_$1                     ( In Foo#crash )
+[   setInst] tv[Int]                  ( In Foo#crash, _$1=tv[Int] )
+[    create] tv[Int]                  ( In Foo#crash )
+[     clone] tv[Int]                  ( Foo#crash )
+
+// With crash above the classes:
+% scalac -Dscalac.debug.tvar ./a.scala 
+[    create] ?tv                      ( In Foo#crash )
+./a.scala:2: error: Invalid type application in TypeVar: List(), List(Int)
+  def crash(x: Dingus[_]): Unit = x match { case m: Bippy[tv] => () }
+                                                  ^
+one error found
+*/