Merge pull request #1876 from adriaanm/ticket-5189-inf

SI-5189 detect unsoundness when inferring type of match

3 files changed, 19 insertions, 6 deletions

diff --git a/src/compiler/scala/tools/nsc/typechecker/Typers.scala b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
index e3fd83f388..979c0f59f4 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Typers.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
@@ -2552,11 +2552,7 @@ trait Typers extends Modes with Adaptations with Tags {
       }
 
 //    body1 = checkNoEscaping.locals(context.scope, pt, body1)
-      val treeWithSkolems = treeCopy.CaseDef(cdef, pat1, guard1, body1) setType body1.tpe
-
-      new TypeMapTreeSubstituter(deskolemizeGADTSkolems).traverse(treeWithSkolems)
-
-      treeWithSkolems // now without skolems, actually
+      treeCopy.CaseDef(cdef, pat1, guard1, body1) setType body1.tpe
     }
 
     // undo adaptConstrPattern's evil deeds, as they confuse the old pattern matcher
@@ -2591,7 +2587,10 @@ trait Typers extends Modes with Adaptations with Tags {
 
       val casesAdapted = if (!needAdapt) casesTyped else casesTyped map (adaptCase(_, mode, resTp))
 
-      treeCopy.Match(tree, selector1, casesAdapted) setType resTp
+      val matchTyped = treeCopy.Match(tree, selector1, casesAdapted) setType resTp
+      if (!newPatternMatching) // TODO: remove this in 2.11 -- only needed for old pattern matcher
+        new TypeMapTreeSubstituter(deskolemizeGADTSkolems).traverse(matchTyped)
+      matchTyped
     }
 
     // match has been typed -- virtualize it if we're feeling experimental
diff --git a/test/files/neg/t5189_inferred.check b/test/files/neg/t5189_inferred.check
new file mode 100644
index 0000000000..9cc5dcc242
--- /dev/null
+++ b/test/files/neg/t5189_inferred.check
@@ -0,0 +1,6 @@
+t5189_inferred.scala:7: error: type mismatch;
+ found   : scala.collection.immutable.Nil.type
+ required: ?A1 where type ?A1
+  f(Invariant(arr): Covariant[Any])(0) = Nil
+                                         ^
+one error found
diff --git a/test/files/neg/t5189_inferred.scala b/test/files/neg/t5189_inferred.scala
new file mode 100644
index 0000000000..e4e8765445
--- /dev/null
+++ b/test/files/neg/t5189_inferred.scala
@@ -0,0 +1,8 @@
+trait Covariant[+A]
+case class Invariant[A](xs: Array[A]) extends Covariant[A]
+
+class Test {
+  val arr = Array("abc")
+  def f[A](v: Covariant[A]) /*inferred!*/ = v match { case Invariant(xs) => xs }
+  f(Invariant(arr): Covariant[Any])(0) = Nil
+}
\ No newline at end of file