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

Author: mielientiev

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

@@ -12,14 +12,15 @@ import core._
 import Flags._
 import Contexts._
 import Names._
-import ast.Positioned
+import ast.{Positioned, Trees, untpd}
 import ast.Trees._
 import Decorators._
 import StdNames._
 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

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
+  }
 }

compiler/test/dotc/tests.scala

@@ -153,6 +153,7 @@ class tests extends CompilerTest {
   @Test def pos_anonClassSubtyping = compileFile(posDir, "anonClassSubtyping", twice)
   @Test def pos_extmethods = compileFile(posDir, "extmethods", twice)
   @Test def pos_companions = compileFile(posDir, "companions", twice)
+  @Test def posVarargsT1625 = compileFiles(posDir + "varargsInMethodsT1625/")
 
   @Test def pos_all = compileFiles(posDir) // twice omitted to make tests run faster
 
@@ -177,6 +178,8 @@ class tests extends CompilerTest {
   @Test def neg_all = compileFiles(negDir, verbose = true, compileSubDirs = false)
   @Test def neg_typedIdents() = compileDir(negDir, "typedIdents")
 
+  @Test def negVarargsT1625 = compileFiles(negDir + "varargsInMethodsT1625/")
+
   val negCustomArgs = negDir + "customArgs/"
 
   @Test def neg_typers() = compileFile(negCustomArgs, "typers")(allowDoubleBindings)

tests/neg/varargsInMethodsT1625/allParamsAreVarArgs.scala

@@ -0,0 +1,3 @@
+trait T3 {
+  def foo(x: String*, y: String*, c: String*): Int // error // error: varargs parameter must come last
+}

tests/neg/varargsInMethodsT1625/caseClassConstructorVarArgs.scala

@@ -0,0 +1,3 @@
+object T5 {
+  case class Abc(x: String*, c: String*) // error //error: varargs parameter must come last AND found: String* required: String
+}

tests/neg/varargsInMethodsT1625/classConstructorVarArgs.scala

@@ -0,0 +1,3 @@
+class Abc(val x: String*, val c: String*) { // error: varargs parameter must come last
+  def test = ???
+}

tests/neg/varargsInMethodsT1625/curriedNegExample.scala

@@ -0,0 +1,3 @@
+trait T2 {
+  def foo(x: String*, y: String*)(z: Boolean*)(u: Int*, l: Int*): Int // error // error: varargs parameter must come last
+}

tests/neg/varargsInMethodsT1625/firstParamIsVarArgs.scala

@@ -0,0 +1,3 @@
+trait T1 {
+  def foo(x: String*, y: String): Int // error: varargs parameter must come last
+}

tests/pos/varargsInMethodsT1625/curriedPosExample.scala

@@ -0,0 +1,3 @@
+trait T2 {
+  def foo(x: String, y: String*)(z: Boolean*)(u: Int, l: Int*): Int
+}

tests/pos/varargsInMethodsT1625/onlyOneVarArgs.scala

@@ -0,0 +1,3 @@
+trait T1 {
+  def foo(x: String*): Int
+}