[backport] SI-5378, unsoundness with type bounds in refinements.

As the comment says:

Not enough to look for abstract types; have to recursively check
the bounds of each abstract type for more abstract types. Almost
certainly there are other exploitable type soundness bugs which
can be seen by bounding a type parameter by an abstract type which
itself is bounded by an abstract type.

SPECIAL: BUY ONE UNSOUNDNESS, GET ONE FREE

In refinement types, only the first parameter list of methods
was being analyzed for unsound uses of abstract types. Second
parameter list and beyond had free unsoundness reign. That bug
as well is fixed here.

4 files changed, 135 insertions, 48 deletions

diff --git a/src/compiler/scala/tools/nsc/typechecker/Typers.scala b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
index 553583e6b7..239fc47867 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Typers.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
@@ -2213,37 +2213,58 @@ trait Typers extends Modes with Adaptations with Tags {
      */
     def checkMethodStructuralCompatible(ddef: DefDef): Unit = {
       val meth = ddef.symbol
-      def fail(pos: Position, msg: String) = unit.error(pos, msg)
-      val tp: Type = meth.tpe match {
-        case mt @ MethodType(_, _)     => mt
-        case NullaryMethodType(restpe) => restpe  // TODO_NMT: drop NullaryMethodType from resultType?
-        case PolyType(_, restpe)       => restpe
-        case _                         => NoType
-      }
-      def nthParamPos(n: Int) = ddef.vparamss match {
-        case xs :: _ if xs.length > n => xs(n).pos
-        case _                        => meth.pos
-      }
-      def failStruct(pos: Position, what: String, where: String = "Parameter") =
-        fail(pos, s"$where type in structural refinement may not refer to $what")
-
-      foreachWithIndex(tp.paramTypes) { (paramType, idx) =>
-        val sym = paramType.typeSymbol
-        def paramPos = nthParamPos(idx)
-
-        if (sym.isAbstractType) {
-          if (!sym.hasTransOwner(meth.owner))
-            failStruct(paramPos, "an abstract type defined outside that refinement")
-          else if (!sym.hasTransOwner(meth))
-            failStruct(paramPos, "a type member of that refinement")
+      def parentString = meth.owner.parentSymbols filterNot (_ == ObjectClass) match {
+        case Nil => ""
+        case xs  => xs.map(_.nameString).mkString(" (of ", " with ", ")")
+      }
+      def fail(pos: Position, msg: String): Boolean = {
+        unit.error(pos, msg)
+        false
+      }
+      /** Have to examine all parameters in all lists.
+       */
+      def paramssTypes(tp: Type): List[List[Type]] = tp match {
+        case mt @ MethodType(_, restpe) => mt.paramTypes :: paramssTypes(restpe)
+        case PolyType(_, restpe)        => paramssTypes(restpe)
+        case _                          => Nil
+      }
+      def resultType = meth.tpe.finalResultType
+      def nthParamPos(n1: Int, n2: Int) =
+        try ddef.vparamss(n1)(n2).pos catch { case _: IndexOutOfBoundsException => meth.pos }
+
+      def failStruct(pos: Position, what: String, where: String = "Parameter type") =
+        fail(pos, s"$where in structural refinement may not refer to $what")
+
+      foreachWithIndex(paramssTypes(meth.tpe)) { (paramList, listIdx) =>
+        foreachWithIndex(paramList) { (paramType, paramIdx) =>
+          val sym = paramType.typeSymbol
+          def paramPos = nthParamPos(listIdx, paramIdx)
+
+          /** Not enough to look for abstract types; have to recursively check the bounds
+           *  of each abstract type for more abstract types. Almost certainly there are other
+           *  exploitable type soundness bugs which can be seen by bounding a type parameter
+           *  by an abstract type which itself is bounded by an abstract type.
+           */
+          def checkAbstract(tp0: Type, what: String): Boolean = {
+            def check(sym: Symbol): Boolean = !sym.isAbstractType || {
+              log(s"""checking $tp0 in refinement$parentString at ${meth.owner.owner.fullLocationString}""")
+              (    (!sym.hasTransOwner(meth.owner) && failStruct(paramPos, "an abstract type defined outside that refinement", what))
+                || (!sym.hasTransOwner(meth) && failStruct(paramPos, "a type member of that refinement", what))
+                || checkAbstract(sym.info.bounds.hi, "Type bound")
+              )
+            }
+            tp0.dealiasWidenChain forall (t => check(t.typeSymbol))
+          }
+          checkAbstract(paramType, "Parameter type")
+
+          if (sym.isDerivedValueClass)
+            failStruct(paramPos, "a user-defined value class")
+          if (paramType.isInstanceOf[ThisType] && sym == meth.owner)
+            failStruct(paramPos, "the type of that refinement (self type)")
         }
-        if (sym.isDerivedValueClass)
-          failStruct(paramPos, "a user-defined value class")
-        if (paramType.isInstanceOf[ThisType] && sym == meth.owner)
-          failStruct(paramPos, "the type of that refinement (self type)")
       }
-      if (tp.resultType.typeSymbol.isDerivedValueClass)
-        failStruct(ddef.tpt.pos, "a user-defined value class", where = "Result")
+      if (resultType.typeSymbol.isDerivedValueClass)
+        failStruct(ddef.tpt.pos, "a user-defined value class", where = "Result type")
     }
 
     def typedUseCase(useCase: UseCase) {
diff --git a/test/files/neg/t5378.check b/test/files/neg/t5378.check
new file mode 100644
index 0000000000..c1460083f6
--- /dev/null
+++ b/test/files/neg/t5378.check
@@ -0,0 +1,31 @@
+t5378.scala:7: error: Type bound in structural refinement may not refer to an abstract type defined outside that refinement
+  def contains = new { def apply[T1 <: T](value: T1) = ??? }
+                                          ^
+t5378.scala:8: error: Type bound in structural refinement may not refer to an abstract type defined outside that refinement
+  def contains1 = new { def apply[T1 <: A1](value: T1) = ??? }
+                                            ^
+t5378.scala:9: error: Type bound in structural refinement may not refer to an abstract type defined outside that refinement
+  def contains2 = new { def apply[T1 <: A2](value: T1) = ??? }
+                                            ^
+t5378.scala:15: error: Type bound in structural refinement may not refer to an abstract type defined outside that refinement
+    new Bippy { def apply[T1 <: T](value: T1) = ??? }
+                                   ^
+t5378.scala:16: error: Type bound in structural refinement may not refer to an abstract type defined outside that refinement
+    new Bippy { def apply[T1 <: B1](value: T1) = ??? }
+                                    ^
+t5378.scala:17: error: Type bound in structural refinement may not refer to an abstract type defined outside that refinement
+    new Bippy { def apply[T1 <: B2](value: T1) = ??? }
+                                    ^
+t5378.scala:21: error: Type bound in structural refinement may not refer to an abstract type defined outside that refinement
+      def apply1[T1 <: B3](value: T1) = ???
+                           ^
+t5378.scala:23: error: Parameter type in structural refinement may not refer to an abstract type defined outside that refinement
+      def apply3(value: B3) = ???
+                 ^
+t5378.scala:28: error: Parameter type in structural refinement may not refer to an abstract type defined outside that refinement
+    def apply1(s: String)(x: Int)(value: T) = ???
+                                  ^
+t5378.scala:29: error: Type bound in structural refinement may not refer to an abstract type defined outside that refinement
+    def apply2[T1 <: T](s: String)(x: Int)(value: T1) = ???
+                                           ^
+10 errors found
diff --git a/test/files/neg/t5378.scala b/test/files/neg/t5378.scala
new file mode 100644
index 0000000000..fa6afa02be
--- /dev/null
+++ b/test/files/neg/t5378.scala
@@ -0,0 +1,54 @@
+import scala.language.reflectiveCalls
+
+class Coll[+T] {
+  type A1 <: T
+  type A2 <: A1
+
+  def contains = new { def apply[T1 <: T](value: T1) = ??? }
+  def contains1 = new { def apply[T1 <: A1](value: T1) = ??? }
+  def contains2 = new { def apply[T1 <: A2](value: T1) = ??? }
+  def contains3 = {
+    trait Bippy {
+      type B1 <: T
+      type B2 <: B1
+    }
+    new Bippy { def apply[T1 <: T](value: T1) = ??? }
+    new Bippy { def apply[T1 <: B1](value: T1) = ??? }
+    new Bippy { def apply[T1 <: B2](value: T1) = ??? }
+    new Bippy {
+      type B3 = B2
+      type B4 = List[B2]
+      def apply1[T1 <: B3](value: T1) = ???
+      def apply2[T1 <: B4](value: T1) = ???
+      def apply3(value: B3) = ???
+      def apply4(value: B4) = value.head
+    }
+  }
+  def contains4 = new {
+    def apply1(s: String)(x: Int)(value: T) = ???
+    def apply2[T1 <: T](s: String)(x: Int)(value: T1) = ???
+  }
+  def containsOk = {
+    trait Bippy {
+      type B1 <: AnyRef
+      type B2 <: B1
+    }
+    new Bippy { def apply[T1 <: AnyRef](value: T1) = ??? }
+    new Bippy { type B1 = String ; def apply[T1 <: B1](value: T1) = ??? }
+    new Bippy { type B2 = String ; def apply[T1 <: B2](value: T1) = ??? }
+  }
+}
+
+object Test {
+  def main(args: Array[String]): Unit = {
+    val xs = new Coll[List[String]]
+    val ys: Coll[Traversable[String]] = xs
+
+    println(ys contains Nil)
+    // java.lang.NoSuchMethodException: Coll$$anon$1.apply(scala.collection.Traversable)
+    //  at java.lang.Class.getMethod(Class.java:1605)
+    //  at Test$.reflMethod$Method1(a.scala:14)
+    //  at Test$.main(a.scala:14)
+    //  at Test.main(a.scala)
+  }
+}
diff --git a/test/pending/neg/t5378.scala b/test/pending/neg/t5378.scala
deleted file mode 100644
index cada29b0a0..0000000000
--- a/test/pending/neg/t5378.scala
+++ /dev/null
@@ -1,19 +0,0 @@
-import language.reflectiveCalls
-
-class Coll[+T] {
-  def contains = new { def apply[T1 <: T](value: T1) = ??? }
-}
-
-object Test {
-  def main(args: Array[String]): Unit = {
-    val xs = new Coll[List[String]]
-    val ys: Coll[Traversable[String]] = xs
-    
-    println(ys contains Nil)
-    // java.lang.NoSuchMethodException: Coll$$anon$1.apply(scala.collection.Traversable)
-    //  at java.lang.Class.getMethod(Class.java:1605)
-    //  at Test$.reflMethod$Method1(a.scala:14)
-    //  at Test$.main(a.scala:14)
-    //  at Test.main(a.scala)
-  }
-}