Backported fix for SI-7753 to 2.10.x.

5 files changed, 123 insertions, 37 deletions

diff --git a/src/reflect/scala/reflect/internal/Types.scala b/src/reflect/scala/reflect/internal/Types.scala
index 2f49995030..15f62bca30 100644
--- a/src/reflect/scala/reflect/internal/Types.scala
+++ b/src/reflect/scala/reflect/internal/Types.scala
@@ -4818,37 +4818,30 @@ trait Types extends api.Types { self: SymbolTable =>
   }
 
   /** Note: This map is needed even for non-dependent method types, despite what the name might imply.
-   */
+    */
   class InstantiateDependentMap(params: List[Symbol], actuals0: List[Type]) extends TypeMap with KeepOnlyTypeConstraints {
     private val actuals      = actuals0.toIndexedSeq
     private val existentials = new Array[Symbol](actuals.size)
-    def existentialsNeeded: List[Symbol] = existentials.filter(_ ne null).toList
-
-    private object StableArg {
-      def unapply(param: Symbol) = Arg unapply param map actuals filter (tp =>
-        tp.isStable && (tp.typeSymbol != NothingClass)
-      )
-    }
-    private object Arg {
-      def unapply(param: Symbol) = Some(params indexOf param) filter (_ >= 0)
-    }
-
-    def apply(tp: Type): Type = mapOver(tp) match {
-      // unsound to replace args by unstable actual #3873
-      case SingleType(NoPrefix, StableArg(arg)) => arg
-      // (soundly) expand type alias selections on implicit arguments,
-      // see depmet_implicit_oopsla* test cases -- typically, `param.isImplicit`
-      case tp1 @ TypeRef(SingleType(NoPrefix, Arg(pid)), sym, targs) =>
-        val arg = actuals(pid)
-        val res = typeRef(arg, sym, targs)
-        if (res.typeSymbolDirect.isAliasType) res.dealias else tp1
-      // don't return the original `tp`, which may be different from `tp1`,
-      // due to dropping annotations
-      case tp1 => tp1
+    def existentialsNeeded: List[Symbol] = existentials.iterator.filter(_ ne null).toList
+
+    private object StableArgTp {
+      // type of actual arg corresponding to param -- if the type is stable
+      def unapply(param: Symbol): Option[Type] = (params indexOf param) match {
+        case -1  => None
+        case pid =>
+          val tp = actuals(pid)
+          if (tp.isStable && (tp.typeSymbol != NothingClass)) Some(tp)
+          else None
+      }
     }
 
-    /* Return the type symbol for referencing a parameter inside the existential quantifier.
-     * (Only needed if the actual is unstable.)
+    /** Return the type symbol for referencing a parameter that's instantiated to an unstable actual argument.
+     *
+     * To soundly abstract over an unstable value (x: T) while retaining the most type information,
+     * use `x.type forSome { type x.type <: T with Singleton}`
+     * `typeOf[T].narrowExistentially(symbolOf[x])`.
+     *
+     * See also: captureThis in AsSeenFromMap.
      */
     private def existentialFor(pid: Int) = {
       if (existentials(pid) eq null) {
@@ -4856,11 +4849,43 @@ trait Types extends api.Types { self: SymbolTable =>
         existentials(pid) = (
           param.owner.newExistential(param.name.toTypeName append nme.SINGLETON_SUFFIX, param.pos, param.flags)
             setInfo singletonBounds(actuals(pid))
-        )
+          )
       }
       existentials(pid)
     }
 
+    private object UnstableArgTp {
+      // existential quantifier and type of corresponding actual arg with unstable type
+      def unapply(param: Symbol): Option[(Symbol, Type)] = (params indexOf param) match {
+        case -1  => None
+        case pid =>
+          val sym = existentialFor(pid)
+          Some((sym, sym.tpe)) // refers to an actual value, must be kind-*
+      }
+    }
+
+    private object StabilizedArgTp {
+      def unapply(param: Symbol): Option[Type] =
+        param match {
+          case StableArgTp(tp)      => Some(tp)  // (1)
+          case UnstableArgTp(_, tp) => Some(tp)  // (2)
+          case _ => None
+        }
+    }
+
+    /** instantiate `param.type` to the (sound approximation of the) type `T`
+     * of the actual argument `arg` that was passed in for `param`
+     *
+     * (1) If `T` is stable, we can just use that.
+     *
+     * (2) SI-3873: it'd be unsound to instantiate `param.type` to an unstable `T`,
+     * so we approximate to `X forSome {type X <: T with Singleton}` -- we can't soundly say more.
+     */
+    def apply(tp: Type): Type = tp match {
+      case SingleType(NoPrefix, StabilizedArgTp(tp)) => tp
+      case _                                         => mapOver(tp)
+    }
+
     //AM propagate more info to annotations -- this seems a bit ad-hoc... (based on code by spoon)
     override def mapOver(arg: Tree, giveup: ()=>Nothing): Tree = {
       // TODO: this should be simplified; in the stable case, one can
@@ -4883,13 +4908,9 @@ trait Types extends api.Types { self: SymbolTable =>
       // Both examples are from run/constrained-types.scala.
       object treeTrans extends Transformer {
         override def transform(tree: Tree): Tree = tree.symbol match {
-          case StableArg(actual) =>
-            gen.mkAttributedQualifier(actual, tree.symbol)
-          case Arg(pid) =>
-            val sym = existentialFor(pid)
-            Ident(sym) copyAttrs tree setType typeRef(NoPrefix, sym, Nil)
-          case _ =>
-            super.transform(tree)
+          case StableArgTp(tp)          => gen.mkAttributedQualifier(tp, tree.symbol)
+          case UnstableArgTp(quant, tp) => Ident(quant) copyAttrs tree setType tp
+          case _                        => super.transform(tree)
         }
       }
       treeTrans transform arg
diff --git a/test/files/neg/t3873.check b/test/files/neg/t3873.check
index 54d6abdf63..f9f413aeaf 100644
--- a/test/files/neg/t3873.check
+++ b/test/files/neg/t3873.check
@@ -1,6 +1,6 @@
 t3873.scala:11: error: type mismatch;
  found   : Test.a.B
- required: a.B
-  wrongf(new A)(a.b) // should not compile -- TODO: improve error message? the "a" is ambiguous
+ required: a.B where val a: A
+  wrongf(new A)(a.b) // should not compile
                   ^
 one error found
diff --git a/test/files/neg/t3873.scala b/test/files/neg/t3873.scala
index e7815f0937..b27b4e9c9d 100644
--- a/test/files/neg/t3873.scala
+++ b/test/files/neg/t3873.scala
@@ -8,5 +8,5 @@ object Test {
 
   val a = new A
   wrongf(a)(a.b)
-  wrongf(new A)(a.b) // should not compile -- TODO: improve error message? the "a" is ambiguous
+  wrongf(new A)(a.b) // should not compile
 }
\ No newline at end of file
diff --git a/test/files/pos/t7753.scala b/test/files/pos/t7753.scala
new file mode 100644
index 0000000000..93ad23f114
--- /dev/null
+++ b/test/files/pos/t7753.scala
@@ -0,0 +1,36 @@
+import scala.language.{ higherKinds, implicitConversions }
+
+trait Foo { type Out }
+
+trait SI {
+  val instance: Foo
+  type Out
+}
+
+object Test {
+  def test {
+    def indirect(si: SI)(v: si.instance.Out) = v
+
+    val foo: Foo { type Out = Int } = ???
+    def conv(i: Foo): SI { type Out = i.Out; val instance: i.type } = ???
+
+    val converted = conv(foo)
+
+    val v1: Int = indirect(converted)(23)  // Okay (after refining the return type `instance` in the return type of `conv`)
+    /*
+    indirect(converted){(v: converted.instance.Out)converted.instance.Out}(
+      23{Int(23)}
+    ){converted.instance.Out};
+    */
+
+    val v2: Int = indirect(conv(foo))(23)  // Used to fail as follows:
+    /*
+    indirect(
+        conv(foo){si.SI{type Out = foo.Out; val instance: si.Test.<refinement>.type}}
+    ){(v: si.instance.Out)si.instance.Out}(
+      23{<error>}
+    ){<error>};
+    */
+
+  }
+}
diff --git a/test/files/pos/t8223.scala b/test/files/pos/t8223.scala
new file mode 100644
index 0000000000..52d6b0098e
--- /dev/null
+++ b/test/files/pos/t8223.scala
@@ -0,0 +1,29 @@
+package p {
+  class ViewEnv[AIn] {
+    type A = AIn
+    class SubView { def has(x: A): Boolean = ??? }
+    def get: SubView = new SubView
+  }
+
+  trait HasA { type A }
+  trait Indexable[R] extends HasA
+  class ArrayTC[AIn] extends Indexable[Array[AIn]] { type A = AIn }
+}
+
+package object p {
+  implicit def arrayTypeClass[A] : ArrayTC[A] = new ArrayTC[A]
+  object intArrayTC extends ArrayTC[Int]
+
+  type EnvAlias[W <: HasA] = ViewEnv[W#A]
+  type SubAlias[W <: HasA] = ViewEnv[W#A]#SubView
+
+  def f0[R](xs: R)(implicit tc: Indexable[R]): ViewEnv[tc.A]#SubView     = new ViewEnv[tc.A]() get
+  def f1[R](xs: R)(implicit tc: Indexable[R]): EnvAlias[tc.type]#SubView = new ViewEnv[tc.A]() get
+  def f2[R](xs: R)(implicit tc: Indexable[R]): SubAlias[tc.type]         = new ViewEnv[tc.A]() get
+
+  def g0 = f0(Array(1)) has 2                   // ok
+  def g1 = f1(Array(1)) has 2                   // ok
+  def g2 = f2(Array(1)) has 2                   // "found: Int(2), required: tc.A"
+  def g3 = f2(Array(1))(new ArrayTC[Int]) has 2 // "found: Int(2), required: tc.A"
+  def g4 = f2(Array(1))(intArrayTC) has 2       // ok
+}