Merge pull request #1630 from m-sp/master

Add error message Parsers.scala:1620 missing type keyword

Author: felixmulder

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

@@ -1623,7 +1623,7 @@ object Parsers {
                 val mod = atPos(in.skipToken()) { Mod.Type() }
                 (mods | Param | ParamAccessor).withAddedMod(mod)
               } else {
-                if (mods.hasFlags) syntaxError("`type' expected")
+                if (mods.hasFlags) syntaxError(TypeParamsTypeExpected(mods, ident()))
                 mods | Param | PrivateLocal
               }
             }

src/dotty/tools/dotc/reporting/diagnostic/messages.scala

@@ -677,5 +677,18 @@ object messages {
            |
            |$fixedVarInAlternative""".stripMargin
     }
+  }  
+    
+  case class TypeParamsTypeExpected(mods: Modifiers, identifier: TermName)(implicit ctx: Context) extends Message(24) {
+    val kind = "Syntax"
+    
+    val msg = hl"""Expected ${"type"} keyword for type parameter $identifier"""
+
+    val explanation = hl"""|This happens when you add modifiers like ${"private"} or ${"protected"}
+                           |to your type parameter definition without adding the ${"type"} keyword.
+                           |
+                           |Add ${"type"} to your code, e.g.:
+                           |${s"trait A[${mods.flags} type $identifier]"}
+                           |""".stripMargin
   }
 }