Fix varargs in methods and constructors (#2135)

* Fix varargs in methods (Issue: #1625)
* Fix minor comments
* Change varargs parameter message
* Fix failed test, fix case for constructor

2 files changed, 33 insertions, 1 deletions

diff --git a/compiler/src/dotty/tools/dotc/parsing/Parsers.scala b/compiler/src/dotty/tools/dotc/parsing/Parsers.scala
index 65c7a290d..b644c94cc 100644
--- a/compiler/src/dotty/tools/dotc/parsing/Parsers.scala
+++ b/compiler/src/dotty/tools/dotc/parsing/Parsers.scala
@@ -12,7 +12,7 @@ import core._
 import Flags._
 import Contexts._
 import Names._
-import ast.Positioned
+import ast.{Positioned, Trees, untpd}
 import ast.Trees._
 import Decorators._
 import StdNames._
@@ -20,6 +20,7 @@ import util.Positions._
 import Constants._
 import ScriptParsers._
 import Comments._
+
 import scala.annotation.{tailrec, switch}
 import util.DotClass
 import rewrite.Rewrites.patch
@@ -1800,6 +1801,10 @@ object Parsers {
           case _          => syntaxError(AuxConstructorNeedsNonImplicitParameter(), start)
         }
       }
+      val listOfErrors = checkVarArgsRules(result)
+      listOfErrors.foreach { vparam =>
+        syntaxError(VarArgsParamMustComeLast(), vparam.tpt.pos)
+      }
       result
     }
 
@@ -1921,6 +1926,21 @@ object Parsers {
       }
     }
 
+
+
+    private def checkVarArgsRules(vparamss: List[List[untpd.ValDef]]): List[untpd.ValDef] = {
+      def isVarArgs(tpt: Trees.Tree[Untyped]): Boolean = tpt match {
+        case PostfixOp(_, op) if op.name == nme.raw.STAR => true
+        case _ => false
+      }
+
+      vparamss.flatMap { params =>
+        if (params.nonEmpty) {
+          params.init.filter(valDef => isVarArgs(valDef.tpt))
+        } else List()
+      }
+    }
+
     /** DefDef ::= DefSig (`:' Type [`=' Expr] | "=" Expr)
      *           | this ParamClause ParamClauses `=' ConstrExpr
      *  DefDcl ::= DefSig `:' Type
diff --git a/compiler/src/dotty/tools/dotc/reporting/diagnostic/messages.scala b/compiler/src/dotty/tools/dotc/reporting/diagnostic/messages.scala
index 6fa056646..57365658e 100644
--- a/compiler/src/dotty/tools/dotc/reporting/diagnostic/messages.scala
+++ b/compiler/src/dotty/tools/dotc/reporting/diagnostic/messages.scala
@@ -1209,4 +1209,16 @@ object messages {
            |${parents.mkString("  - ", "\n  - ", "")}
            |""".stripMargin
   }
+
+  case class VarArgsParamMustComeLast()(implicit ctx: Context)
+    extends Message(IncorrectRepeatedParameterSyntaxID) {
+    override def msg: String = "varargs parameter must come last"
+
+    override def kind: String = "Syntax"
+
+    override def explanation: String =
+      hl"""|The varargs field must be the last field in the method signature.
+           |Attempting to define a field in a method signature after a varargs field is an error.
+           |""".stripMargin
+  }
 }