Added auto-tupling.

Auto-tupling should satisfy the following spec.

1. An application `f(args)` where `f` is a non-overloaded method which has a single, non-repeated parameter as its
first parameter list and where args consists of two or more arguments is expanded to `f((args))`.

2. A constructor pattern `C(args)` where `C.unapply` is a non-overloaded method which has a single, non-repeated parameter as its first parameter list and where args consists of two or more arguments is expanded to `C((args))`.

Auto-tupling can be disabled by language feature "noAutoTupling".

Conflicts:
	test/dotc/tests.scala

6 files changed, 51 insertions, 5 deletions

diff --git a/src/dotty/tools/dotc/core/Definitions.scala b/src/dotty/tools/dotc/core/Definitions.scala
index 5c2890f29..bcf2bb74c 100644
--- a/src/dotty/tools/dotc/core/Definitions.scala
+++ b/src/dotty/tools/dotc/core/Definitions.scala
@@ -215,7 +215,7 @@ class Definitions {
   lazy val JavaSerializableClass        = ctx.requiredClass("java.lang.Serializable")
   lazy val ComparableClass              = ctx.requiredClass("java.lang.Comparable")
   lazy val ProductClass                 = ctx.requiredClass("scala.Product")
-  lazy val LanguageModuleClass          = ctx.requiredModule("dotty.language").moduleClass
+  lazy val LanguageModuleClass          = ctx.requiredModule("dotty.language").moduleClass.asClass
 
   // Annotation base classes
   lazy val AnnotationClass              = ctx.requiredClass("scala.annotation.Annotation")
diff --git a/src/dotty/tools/dotc/core/TypeOps.scala b/src/dotty/tools/dotc/core/TypeOps.scala
index 4ace0bebe..22a86766b 100644
--- a/src/dotty/tools/dotc/core/TypeOps.scala
+++ b/src/dotty/tools/dotc/core/TypeOps.scala
@@ -5,6 +5,7 @@ import Contexts._, Types._, Symbols._, Names._, Flags._, Scopes._
 import SymDenotations._
 import config.Printers._
 import Decorators._
+import StdNames._
 import util.SimpleMap
 
 trait TypeOps { this: Context =>
@@ -300,6 +301,10 @@ trait TypeOps { this: Context =>
     def hasOption = ctx.base.settings.language.value exists (s => s == featureName || s == "_")
     hasImport || hasOption
   }
+
+  /** Is auto-tupling enabled? */
+  def canAutoTuple =
+    !featureEnabled(defn.LanguageModuleClass, nme.noAutoTupling)
 }
 
 object TypeOps {
diff --git a/src/dotty/tools/dotc/core/Types.scala b/src/dotty/tools/dotc/core/Types.scala
index 6dda937d2..a0293d50a 100644
--- a/src/dotty/tools/dotc/core/Types.scala
+++ b/src/dotty/tools/dotc/core/Types.scala
@@ -685,6 +685,13 @@ object Types {
       case _ => Nil
     }
 
+    /** The parameter types in the first parameter section of a PolyType or MethodType, Empty list for others */
+    final def firstParamTypes: List[Type] = this match {
+      case mt: MethodType => mt.paramTypes
+      case pt: PolyType => pt.resultType.firstParamTypes
+      case _ => Nil
+    }
+
     /** Is this either not a method at all, or a parameterless method? */
     final def isParameterless: Boolean = this match {
       case mt: MethodType => false
diff --git a/src/dotty/tools/dotc/typer/Applications.scala b/src/dotty/tools/dotc/typer/Applications.scala
index feaf678a2..4d26532d6 100644
--- a/src/dotty/tools/dotc/typer/Applications.scala
+++ b/src/dotty/tools/dotc/typer/Applications.scala
@@ -434,8 +434,17 @@ trait Applications extends Compatibility { self: Typer =>
   def typedApply(tree: untpd.Apply, pt: Type)(implicit ctx: Context): Tree = {
 
     def realApply(implicit ctx: Context): Tree = track("realApply") {
-      val proto = new FunProto(tree.args, pt, this)
+      var proto = new FunProto(tree.args, pt, this)
       val fun1 = typedExpr(tree.fun, proto)
+
+      // Warning: The following line is dirty and fragile. We record that auto-tupling was demanded as
+      // a side effect in adapt. If it was, we assume the tupled proto-type in the rest of the application.
+      // This crucially relies on he fact that `proto` is used only in a single call of `adapt`,
+      // otherwise we would get possible cross-talk between different `adapt` calls using the same
+      // prototype. A cleaner alternative would be to return a modified prototype from `adapt` together with
+      // a modified tree but this would be more convoluted and less efficient.
+      if (proto.isTupled) proto = proto.tupled
+
       methPart(fun1).tpe match {
         case funRef: TermRef =>
           tryEither { implicit ctx =>
@@ -676,7 +685,10 @@ trait Applications extends Compatibility { self: Typer =>
         var argTypes = unapplyArgs(unapplyApp.tpe)
         for (argType <- argTypes) assert(!argType.isInstanceOf[TypeBounds], unapplyApp.tpe.show)
         val bunchedArgs = argTypes match {
-          case argType :: Nil if argType.isRepeatedParam => untpd.SeqLiteral(args) :: Nil
+          case argType :: Nil =>
+            if (argType.isRepeatedParam) untpd.SeqLiteral(args) :: Nil
+            else if (args.lengthCompare(1) > 0 && ctx.canAutoTuple) untpd.Tuple(args) :: Nil
+            else args
           case _ => args
         }
         if (argTypes.length != bunchedArgs.length) {
diff --git a/src/dotty/tools/dotc/typer/ProtoTypes.scala b/src/dotty/tools/dotc/typer/ProtoTypes.scala
index b4068408b..74be3f4cd 100644
--- a/src/dotty/tools/dotc/typer/ProtoTypes.scala
+++ b/src/dotty/tools/dotc/typer/ProtoTypes.scala
@@ -187,6 +187,20 @@ object ProtoTypes {
       typer.adapt(targ, formal)
     }
 
+    private var myTupled: Type = NoType
+
+    /** The same proto-type but with all arguments combined in a single tuple */
+    def tupled: FunProto = myTupled match {
+      case pt: FunProto =>
+        pt
+      case _ =>
+        myTupled = new FunProto(untpd.Tuple(args) :: Nil, resultType, typer)
+        tupled
+    }
+
+    /** Somebody called the `tupled` method of this prototype */
+    def isTupled: Boolean = myTupled.isInstanceOf[FunProto]
+
     override def toString = s"FunProto(${args mkString ","} => $resultType)"
 
     def map(tm: TypeMap)(implicit ctx: Context): FunProto =
diff --git a/src/dotty/tools/dotc/typer/Typer.scala b/src/dotty/tools/dotc/typer/Typer.scala
index 17c77be89..f961a4544 100644
--- a/src/dotty/tools/dotc/typer/Typer.scala
+++ b/src/dotty/tools/dotc/typer/Typer.scala
@@ -1072,8 +1072,16 @@ class Typer extends Namer with TypeAssigner with Applications with Implicits wit
       }
     }
 
-    def adaptToArgs(wtp: Type, pt: FunProto) = wtp match {
-      case _: MethodType | _: PolyType => tree
+    def adaptToArgs(wtp: Type, pt: FunProto): Tree = wtp match {
+      case _: MethodType | _: PolyType =>
+        def isUnary = wtp.firstParamTypes match {
+          case ptype :: Nil => !ptype.isRepeatedParam
+          case _ => false
+        }
+        if (pt.args.lengthCompare(1) > 0 && isUnary && ctx.canAutoTuple)
+          adaptToArgs(wtp, pt.tupled)
+        else
+          tree
       case _ => tryInsertApply(tree, pt) {
         val more = tree match {
           case Apply(_, _) => " more"