Merge pull request #1402 from dotty-staging/fix-wildcard-protos

Fix wildcard protos

Author: smarter

src/dotty/tools/dotc/printing/RefinedPrinter.scala

@@ -96,15 +96,15 @@ class RefinedPrinter(_ctx: Context) extends PlainPrinter(_ctx) {
 
   override def toText(tp: Type): Text = controlled {
     def toTextTuple(args: List[Type]): Text =
-      "(" ~ toTextGlobal(args, ", ") ~ ")"
+      "(" ~ Text(args.map(argText), ", ") ~ ")"
     def toTextFunction(args: List[Type]): Text =
       changePrec(GlobalPrec) {
         val argStr: Text =
           if (args.length == 2 && !defn.isTupleType(args.head))
-            atPrec(InfixPrec) { toText(args.head) }
+            atPrec(InfixPrec) { argText(args.head) }
           else
             toTextTuple(args.init)
-        argStr ~ " => " ~ toText(args.last)
+        argStr ~ " => " ~ argText(args.last)
       }
     homogenize(tp) match {
       case AppliedType(tycon, args) =>

src/dotty/tools/dotc/typer/Typer.scala

@@ -582,7 +582,10 @@ class Typer extends Namer with TypeAssigner with Applications with Implicits wit
 
   private def decomposeProtoFunction(pt: Type, defaultArity: Int)(implicit ctx: Context): (List[Type], Type) = pt match {
     case _ if defn.isFunctionType(pt) =>
-      (pt.dealias.argInfos.init, pt.dealias.argInfos.last)
+      // if expected parameter type(s) are wildcards, approximate from below.
+      // if expected result type is a wildcard, approximate from above.
+      // this can type the greatest set of admissible closures.
+      (pt.dealias.argTypesLo.init, pt.dealias.argTypesHi.last)
     case SAMType(meth) =>
       val mt @ MethodType(_, paramTypes) = meth.info
       (paramTypes, mt.resultType)

tests/pos/conformsWild.scala

@@ -0,0 +1,11 @@
+object Test {
+
+  val x: Function1[_, _] = (x: String) => 1
+
+  val y: Function1[_, _] = x => 1
+  val y0: Function1[_, _] = x => x
+  val y1: Function1[_, Nothing] = x => x
+
+  val z: (_, _) = (1, 2)
+
+}