Fix tests and add check files

Author: odersky

compiler/src/dotty/tools/dotc/core/tasty/TreePickler.scala

@@ -699,7 +699,7 @@ class TreePickler(pickler: TastyPickler) {
         case ex: AssertionError =>
           println(i"error when pickling tree $tree")
           throw ex
-       case ex: MatchError =>
+        case ex: MatchError =>
           println(i"error when pickling tree $tree")
           throw ex
       }

tests/neg/i12448.scala

@@ -1,5 +1,5 @@
 object Main {
   def mkArray[T <: A]: T#AType // error // error
-  mkArray[Array] // was: "assertion failed: invalid prefix HKTypeLambda..."
-  val x = mkArray[Array]
+  mkArray[Array] // was: "assertion failed: invalid prefix HKTypeLambda..." // error
+  val x = mkArray[Array] // error
 }

tests/neg/i16842.check

@@ -0,0 +1,4 @@
+-- Error: tests/neg/i16842.scala:24:7 ----------------------------------------------------------------------------------
+24 |  Liter(SemanticArray[SemanticInt.type], x) // error
+   |       ^
+   |       invalid new prefix (dim: Int): SemanticArray[SemanticInt.type] cannot replace ty.type in type ty.T

tests/neg/i16842.scala

@@ -21,5 +21,5 @@ def typecheckArrayLiter(
     a: ArrayLiter
 ): Liter[SemanticArray[SemanticType]] = {
   val x: List[Expr2[SemanticInt.type]] = List()
-  Liter(SemanticArray[SemanticInt.type], x) // error // error
+  Liter(SemanticArray[SemanticInt.type], x) // error
 }

tests/neg/i18058.check

@@ -0,0 +1,4 @@
+-- Error: tests/neg/i18058.scala:4:21 ----------------------------------------------------------------------------------
+4 |type G = (f: _ <: F) => f.A // error
+  |                     ^
+  |                     invalid new prefix  <: F cannot replace f.type in type f.A