Merge pull request #2523 from biboudis/fix-2512

Fix #2512: Implicit keyword not allowed on return types

Author: felixmulder

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

@@ -774,7 +774,10 @@ object Parsers {
       in.token match {
         case ARROW => functionRest(t :: Nil)
         case FORSOME => syntaxError(ExistentialTypesNoLongerSupported()); t
-        case _ => t
+        case _ =>
+          if (isImplicit && !t.isInstanceOf[ImplicitFunction])
+            syntaxError("Types with implicit keyword can only be function types", Position(start, start + nme.IMPLICITkw.asSimpleName.length))
+          t
       }
     }
 

tests/neg/i2512.scala

@@ -0,0 +1,10 @@
+
+object Test {
+
+  def foo0(): implicit Int => Int = ???
+  val foo01: implicit (String, Int) => Int = ???
+
+  def foo1(f: Int => implicit Int): Int = ??? // error
+  def foo2(): implicit Int = ??? // error
+  def foo3(): Int => implicit Int = ??? // error
+}