Adress reviewers comments

Author: odersky

src/dotty/tools/dotc/ast/TreeInfo.scala

@@ -280,7 +280,7 @@ trait TreeInfo[T >: Untyped <: Type] { self: Trees.Instance[T] =>
 trait UntypedTreeInfo extends TreeInfo[Untyped] { self: Trees.Instance[Untyped] =>
   import TreeInfo._
 
-  def isFunctionWithImplicitParamType(tree: Tree) = tree match {
+  def isFunctionWithUnknownParamType(tree: Tree) = tree match {
     case untpd.Function(args, _) =>
       args.exists {
         case ValDef(_, tpt, _) => tpt.isEmpty

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

@@ -554,12 +554,11 @@ trait Applications extends Compatibility { self: Typer with Dynamic =>
       if (proto.isTupled) proto = proto.tupled
 
       // If some of the application's arguments are function literals without explicitly declared
-      // parameter types, and the expected type is a value type, relate the
-      // normalized result type of the application with the expected type through `<:<`.
-      // This can add more constraints which help sharpen the inferred parameter
-      // types for the argument function literal(s).
-      // This tweak is needed to make i1348 compile.
-      if (tree.args.exists(untpd.isFunctionWithImplicitParamType(_)))
+      // parameter types, relate the normalized result type of the application with the
+      // expected type through `constrainResult`. This can add more constraints which
+      // help sharpen the inferred parameter types for the argument function literal(s).
+      // This tweak is needed to make i1378 compile.
+      if (tree.args.exists(untpd.isFunctionWithUnknownParamType(_)))
         if (!constrainResult(fun1.tpe.widen, proto.derivedFunProto(resultType = pt)))
           typr.println(i"result failure for $tree with type ${fun1.tpe.widen}, expected = $pt")
 

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

@@ -599,7 +599,10 @@ class Typer extends Namer with TypeAssigner with Applications with Implicits wit
       val params = args.asInstanceOf[List[untpd.ValDef]]
 
       pt match {
-        case pt: TypeVar if untpd.isFunctionWithImplicitParamType(tree) =>
+        case pt: TypeVar if untpd.isFunctionWithUnknownParamType(tree) =>
+          // try to instantiate `pt` if this is possible. If it does not
+          // work the error will be reported later in `inferredParam`,
+          // when we try to infer the parameter type.
           isFullyDefined(pt, ForceDegree.noBottom)
         case _ =>
       }