Add regression tests

Closes lampepfl#3058
Closes lampepfl#10943
Closes lampepfl#12216
Closes lampepfl#12655

Author: pweisenburger

tests/neg/i10943.check

@@ -0,0 +1,7 @@
+-- [E007] Type Mismatch Error: tests/neg/i10943.scala:5:10 -------------------------------------------------------------
+5 |  val a = new A : Int // error
+  |          ^^^^^
+  |          Found:    T.A
+  |          Required: Int
+  |
+  | longer explanation available when compiling with `-explain`

tests/neg/i10943.scala

@@ -0,0 +1,6 @@
+import language.experimental.fewerBraces
+
+object T:
+  class A
+  val a = new A : Int // error
+end T

tests/pos/i12216.scala

@@ -0,0 +1,24 @@
+import scala.language.implicitConversions
+
+sealed abstract class CtorType[P]
+
+object CtorType {
+  final class Props[P] extends CtorType[P] {
+    def whyHelloThere(props: P): Unit = ()
+  }
+}
+
+trait Comp[P, CT[p] <: CtorType[p]] {
+  val ctor: CT[P]
+}
+object Comp {
+  implicit def autoCtor[P, CT[p] <: CtorType[p]](c: Comp[P, CT]): CT[P] = c.ctor
+}
+
+object Test {
+  val comp: Comp[Int, CtorType.Props] = ???
+
+  comp.whyHelloThere(3)
+
+  Comp.autoCtor(comp).whyHelloThere(3)
+}

tests/pos/i12655.scala

@@ -0,0 +1,12 @@
+trait Signature:
+  type Impl[A, U]
+
+type Operation[Z <: Signature, A, U] = (z: Z) => z.Impl[A, U]
+
+case class Perform0[Z <: Signature, A, U](op: Operation[Z, A, U])
+
+case class Perform1[Z <: Signature, A, U](op: (z: Z) => z.Impl[A, U])
+
+def perform0[Z <: Signature, A, U](op: Operation[Z, A, U]): Unit = ???
+
+def perform1[Z <: Signature, A, U](op: (z: Z) => z.Impl[A, U]): Unit = ???

tests/pos/i3058.scala

@@ -0,0 +1,14 @@
+trait C[T] { type U }
+
+object C { type Aux[X, Y] = C[X] { type U = Y } }
+
+
+def a: C[Int] { type U = Int } = ???
+
+def b[T](c: C[T]): C[T] { type U = c.U } = ???
+
+
+def t[T, U](c: C.Aux[T, U]) = ???
+
+
+object Test { t(b(a)) }