Fix #1444: Add implicit arguments to supertraits

If a super trait is given as a type (i.e. no argument list), implicit args were
not passed. This is fixed now. Also, we now check for parameterized traits lacking
type arguments in Typer instead of in Mixin.

Fixes #1444.

Author: odersky

src/dotty/tools/dotc/transform/Mixin.scala

@@ -189,16 +189,17 @@ class Mixin extends MiniPhaseTransform with SymTransformer { thisTransform =>
       var argNum = 0
       def nextArgument() = initArgs.get(mixin) match {
         case Some(arguments) =>
-          try arguments(argNum) finally argNum += 1
+          val result = arguments(argNum)
+          argNum += 1
+          result
         case None =>
-          val (msg, pos) = impl.parents.find(_.tpe.typeSymbol == mixin) match {
-            case Some(parent) => ("lacks argument list", parent.pos)
-            case None =>
-              ("""is indirectly implemented,
-                 |needs to be implemented directly so that arguments can be passed""".stripMargin,
-               cls.pos)
-          }
-          ctx.error(i"parameterized $mixin $msg", pos)
+          assert(
+              impl.parents.forall(_.tpe.typeSymbol != mixin),
+              i"missing parameters for $mixin from $impl should have been caught in typer")
+          ctx.error(
+              em"""parameterized $mixin is indirectly implemented,
+                  |needs to be implemented directly so that arguments can be passed""",
+              cls.pos)
           EmptyTree
       }
 

src/dotty/tools/dotc/typer/Typer.scala

@@ -1132,8 +1132,43 @@ class Typer extends Namer with TypeAssigner with Applications with Implicits wit
   def typedClassDef(cdef: untpd.TypeDef, cls: ClassSymbol)(implicit ctx: Context) = track("typedClassDef") {
     val TypeDef(name, impl @ Template(constr, parents, self, _)) = cdef
     val superCtx = ctx.superCallContext
+
+    /** If `ref` is an implicitly parameterized trait, pass an implicit argument list.
+     *  Otherwise, if `ref` is a parameterized trait, error.
+     *  Note: Traits and classes currently always have at least an empty parameter list ()
+     *        before the implicit parameters (this is inserted if not given in source).
+     *        We skip this parameter list when deciding whether a trait is parameterless or not.
+     *  @param ref   The tree referring to the (parent) trait
+     *  @param psym  Its type symbol
+     *  @param cinfo The info of its constructor
+     */
+    def maybeCall(ref: Tree, psym: Symbol, cinfo: Type): Tree = cinfo match {
+      case cinfo: PolyType =>
+        maybeCall(ref, psym, cinfo.resultType)
+      case cinfo @ MethodType(Nil, _) if cinfo.resultType.isInstanceOf[ImplicitMethodType] =>
+        val icall = New(ref).select(nme.CONSTRUCTOR).appliedToNone
+        typedExpr(untpd.TypedSplice(icall))(superCtx)
+      case cinfo @ MethodType(Nil, _) if !cinfo.resultType.isInstanceOf[MethodType] =>
+        ref
+      case cinfo: MethodType =>
+        if (!ctx.erasedTypes) { // after constructors arguments are passed in super call.
+          typr.println(i"constr type: $cinfo")
+          ctx.error(em"parameterized $psym lacks argument list", ref.pos)
+        }
+        ref
+      case _ =>
+        ref
+    }
+
     def typedParent(tree: untpd.Tree): Tree =
-      if (tree.isType) typedType(tree)(superCtx)
+      if (tree.isType) {
+        val result = typedType(tree)(superCtx)
+        val psym = result.tpe.typeSymbol
+        if (psym.is(Trait) && !cls.is(Trait) && !cls.superClass.isSubClass(psym))
+          maybeCall(result, psym, psym.primaryConstructor.info)
+        else
+          result
+      }
       else {
         val result = typedExpr(tree)(superCtx)
         checkParentCall(result, cls)

tests/neg/i1263.scala

@@ -0,0 +1,33 @@
+object Test {
+  trait Foo(val s: String)
+
+  val foo1 = new Foo("bar") {}
+  val foo2 = new Foo { override val s = "bar" } // error: parameterized trait lacks argument list
+  def main(args: Array[String]): Unit = {
+    assert(foo1.s == "bar")
+    assert(foo2.s == "bar")
+  }
+}
+object Test1 {
+  trait Foo(private val s0: String) {
+    def s = s0
+  }
+
+  val foo1 = new Foo("bar") {}
+  def main(args: Array[String]): Unit = {
+    assert(foo1.s == "bar")
+  }
+}
+object Test2 {
+  trait Foo(protected val s: String)
+
+  val foo1 = new Foo("bar") {}
+}
+object Test3 {
+  trait Foo(final val s: String)
+
+  val foo1 = new Foo("bar") {}
+  def main(args: Array[String]): Unit = {
+    assert(foo1.s == "bar")
+  }
+}

tests/neg/traitParamsMixin.scala

@@ -2,8 +2,6 @@ trait T(x: Int) {
   def f = x
 }
 
-class C extends T  // error
-
 trait U extends T
 
 class D extends U {  // error

tests/neg/traitParamsTyper.scala

@@ -2,6 +2,8 @@ trait T(x: Int) {
   def f = x
 }
 
+class C extends T // error
+
 class C(x: Int) extends T() // error
 
 trait U extends C with T

tests/pos/i1444.scala

@@ -0,0 +1,14 @@
+object Test {
+
+class Cls(implicit x:X)
+class ClsImpl extends Cls //this works
+
+trait Tr1(implicit x:X)
+class TrtImpl extends Tr1 //Compiler: Error: parameterized trait Tr1 lacks argument list
+
+trait Tr2()(implicit x:X)
+class Tr2Impl extends Tr2() //this works
+
+trait X
+implicit object AnX extends X
+}

tests/run/i1263.scala

@@ -2,10 +2,8 @@ object Test {
   trait Foo(val s: String)
 
   val foo1 = new Foo("bar") {}
-  val foo2 = new Foo { override val s = "bar" }
   def main(args: Array[String]): Unit = {
     assert(foo1.s == "bar")
-    assert(foo2.s == "bar")
   }
 }
 object Test1 {
@@ -22,7 +20,6 @@ object Test2 {
   trait Foo(protected val s: String)
 
   val foo1 = new Foo("bar") {}
-  val foo2 = new Foo { override val s = "bar" }
 }
 object Test3 {
   trait Foo(final val s: String)