Fix #1784: allow to omit types for local implicit vals

Author: odersky

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

@@ -998,11 +998,17 @@ class Namer { typer: Typer =>
           lhsType // keep constant types that fill in for a non-constant (to be revised when inline has landed).
         else inherited
       else {
-        if (sym is Implicit) {
-          val resStr = if (mdef.isInstanceOf[DefDef]) "result " else ""
-          ctx.error(s"${resStr}type of implicit definition needs to be given explicitly", mdef.pos)
+        def missingType(modifier: String) = {
+          ctx.error(s"${modifier}type of implicit definition needs to be given explicitly", mdef.pos)
           sym.resetFlag(Implicit)
+
         }
+        if (sym is Implicit)
+          mdef match {
+            case _: DefDef => missingType("result")
+            case _: ValDef if sym.owner.isType => missingType("")
+            case _ =>
+          }
         lhsType orElse WildcardType
       }
     }

tests/pos/implicits.scala

@@ -6,4 +6,9 @@ object Test {
 
   val x: X = Byte.MinValue
 
+  def foo() = {
+    implicit val x = "abc"
+    implicitly[String]
+  }
+
 }