Allow implicit-by-name parameters

Author: odersky

compiler/src/dotty/tools/dotc/parsing/Parsers.scala

@@ -1765,12 +1765,8 @@ object Parsers {
               TypeTree()  // XX-METHOD-INFER
             } else {
               accept(COLON)
-              if (in.token == ARROW) {
-                if (owner.isTypeName && !(mods is Local))
-                  syntaxError(s"${if (mods is Mutable) "`var'" else "`val'"} parameters may not be call-by-name")
-                else if (imods.hasFlags)
-                  syntaxError("implicit parameters may not be call-by-name")
-              }
+              if (in.token == ARROW && owner.isTypeName && !(mods is Local))
+                syntaxError(s"${if (mods is Mutable) "`var'" else "`val'"} parameters may not be call-by-name")
               paramType()
             }
           val default =

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

@@ -1880,7 +1880,8 @@ class Typer extends Namer with TypeAssigner with Applications with Implicits wit
           val args = (wtp.paramNames, wtp.paramTypes).zipped map { (pname, formal) =>
             def implicitArgError(msg: String => String) =
               errors += (() => msg(em"parameter $pname of $methodStr"))
-            inferImplicitArg(formal, implicitArgError, tree.pos.endPos)
+            if (errors.nonEmpty) EmptyTree
+            else inferImplicitArg(formal.widenExpr, implicitArgError, tree.pos.endPos)
           }
           if (errors.nonEmpty) {
             // If there are several arguments, some arguments might already