Revert "SI-1786 incorporate defined bounds in inference"

Have to revert because the stricter bounds that it inferred break e.g., slick.
(Backstop for that added as pos/t1786-counter.scala, as minimized by Jason)
Worse, the fix was compilation order-dependent.

There's a less invasive fix (SI-6169) that could be generalized
in `sharpenQuantifierBounds` (used in `skolemizeExistential`),
but I'd rather not mess with existentials at this point.

This reverts commit e28c3edda4dd405ed382227d2a688b799bf33c72.

Conflicts:
	src/compiler/scala/tools/nsc/typechecker/Typers.scala
	test/files/pos/t1786.scala

1 files changed, 38 insertions, 0 deletions

diff --git a/test/files/pos/t1786-counter.scala b/test/files/pos/t1786-counter.scala
new file mode 100644
index 0000000000..c1ad2c204f
--- /dev/null
+++ b/test/files/pos/t1786-counter.scala
@@ -0,0 +1,38 @@
+trait ShapeLevel
+
+object Fail {
+  abstract class ProductNodeShape[Level <: ShapeLevel, C, M <: C, U <: C, P <: C] extends Shape[Level, M, U, P] {
+    def copy(shapes: Seq[Shape[_, _, _, _]]): Shape[Level, _, _, _]
+  }
+
+  abstract class Shape[Level <: ShapeLevel, -Mixed_, Unpacked_, Packed_]
+
+  final class TupleShape[Level <: ShapeLevel, M <: Product, U <: Product, P <: Product](val shapes: Shape[_, _, _, _]*) extends ProductNodeShape[Level, Product, M, U, P] {
+    def copy(shapes: Seq[Shape[_, _, _, _]]): Shape[Level, _, _, _] = ???
+  }
+
+  trait ShapeLevel
+}
+
+object Ok {
+  abstract class Shape[Level <: ShapeLevel, -Mixed_, Unpacked_, Packed_]
+
+  abstract class ProductNodeShape[Level <: ShapeLevel, C, M <: C, U <: C, P <: C] extends Shape[Level, M, U, P] {
+    def copy(shapes: Seq[Shape[_, _, _, _]]): Shape[Level, _, _, _]
+  }
+
+  final class TupleShape[Level <: ShapeLevel, M <: Product, U <: Product, P <: Product](val shapes: Shape[_, _, _, _]*) extends ProductNodeShape[Level, Product, M, U, P] {
+    def copy(shapes: Seq[Shape[_, _, _, _]]): Shape[Level, _, _, _] = ???
+  }
+}
+
+// This is why we reverted the fix for SI-1786 -- see SI-6169 for a potential alternative that could be extended to cover this.
+// both objects type check on 2.10.3, but only Ok was accepted by 2.11 after the original fix to SI-1786.
+// Fail results in:
+/*
+t1786-counter.scala:10: error: class TupleShape needs to be abstract, since method copy in class ProductNodeShape of type (shapes: Seq[Fail.Shape[_, _, _, _]])Fail.Shape[Level, _, _, _] is not defined
+(Note that Seq[Fail.Shape[_, _, _, _]] does not match Seq[Fail.Shape[_ <: Fail.ShapeLevel, _, _, _]]: their type parameters differ)
+  final class TupleShape[Level <: ShapeLevel, M <: Product, U <: Product, P <: Product](val shapes: Shape[_, _, _, _]*) extends ProductNodeShape[Level, Product, M, U, P] {
+              ^
+one error found
+*/
\ No newline at end of file