Roll Uncurry into Erasure

Making cpy recompute types uncovered errors in uncurry. In a nutshell,
the intermediate Apply nodes of a curried function were ill-typed, which
caused errors produced by TypeAssigner. These nodes were eliminated down the
road, but the errors are already issued.

I did not find a good way to treat uncurry as a treetransform. Since it is rather
trivial, it did not seem warranted to make it a full transformer either. So in
the end the uncurry functionality became part of erasure.

Author: odersky

src/dotty/tools/dotc/Compiler.scala

@@ -32,9 +32,7 @@ class Compiler {
            new TypeTestsCasts,
            new InterceptedMethods,
            new Literalize),
-      List(new Erasure)//,
-      //List(new UncurryTreeTransform
-      //  /* , new Constructors */)
+      List(new Erasure)
     )
 
   var runId = 1

src/dotty/tools/dotc/core/transform/Erasure.scala

@@ -107,7 +107,8 @@ class Erasure(isJava: Boolean, isSemi: Boolean, isConstructor: Boolean, wildcard
    *   - For T1 & T2, erasure(T1)  (??)
    *   - For T1 | T2, the first base class in the linearization of T which is also a base class of T2
    *   - For a method type (Fs)scala.Unit, (|Fs|)scala.Unit.
-   *   - For any other method type (Fs)T, (|Fs|)|T|.
+   *   - For any other uncurried method type (Fs)T, (|Fs|)|T|.
+   *   - For a curried method type (Fs1)(Fs2)T, (|Fs1|,Es2)ET where (Es2)ET = |(Fs2)T|.
    *   - For a polymorphic type, the erasure of its result type.
    *   - For the class info type of java.lang.Object, the same type without any parents.
    *   - For a class info type of a value class, the same type without any parents.
@@ -140,8 +141,13 @@ class Erasure(isJava: Boolean, isSemi: Boolean, isConstructor: Boolean, wildcard
       this(tp.baseTypeRef(lubClass(tp1, tp2)))
     case tp: MethodType =>
       val paramErasure = erasureFn(tp.isJava, isSemi, isConstructor, wildcardOK)(_)
-      tp.derivedMethodType(
-        tp.paramNames, tp.paramTypes.mapConserve(paramErasure), eraseResult(tp.resultType))
+      val formals = tp.paramTypes.mapConserve(paramErasure)
+      eraseResult(tp.resultType) match {
+        case rt: MethodType =>
+          tp.derivedMethodType(tp.paramNames ++ rt.paramNames, formals ++ rt.paramTypes, rt.resultType)
+        case rt =>
+          tp.derivedMethodType(tp.paramNames, formals, rt)
+      }
     case tp: PolyType =>
       this(tp.resultType)
     case tp @ ClassInfo(pre, cls, classParents, decls, _) =>

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

@@ -264,13 +264,28 @@ object Erasure {
 
     override def typedApply(tree: untpd.Apply, pt: Type)(implicit ctx: Context): Tree = {
       val Apply(fun, args) = tree
-      val fun1 = typedExpr(fun, WildcardType)
-      fun1.tpe.widen match {
-        case mt: MethodType =>
-          val args1 = args.zipWithConserve(mt.paramTypes)(typedExpr)
-          untpd.cpy.Apply(tree)(fun1, args1) withType mt.resultType
+      fun match {
+        case fun: Apply =>
+          typedApply(fun, pt)(ctx.fresh.setTree(tree))
         case _ =>
-          throw new MatchError(i"tree $tree has uxpected type of function ${fun1.tpe.widen}, was ${fun.typeOpt.widen}")
+          def nextOuter(ctx: Context): Context =
+            if (ctx.outer.tree eq tree) nextOuter(ctx.outer) else ctx.outer
+          def contextArgs(tree: untpd.Apply)(implicit ctx: Context): List[untpd.Tree] =
+            ctx.tree match {
+              case enclApp @ Apply(enclFun, enclArgs) if enclFun eq tree =>
+                enclArgs ++ contextArgs(enclApp)(nextOuter(ctx))
+              case _ =>
+                Nil
+            }
+          val allArgs = args ++ contextArgs(tree)
+          val fun1 = typedExpr(fun, WildcardType)
+          fun1.tpe.widen match {
+            case mt: MethodType =>
+              val allArgs1 = allArgs.zipWithConserve(mt.paramTypes)(typedExpr)
+              untpd.cpy.Apply(tree)(fun1, allArgs1) withType mt.resultType
+            case _ =>
+              throw new MatchError(i"tree $tree has unexpected type of function ${fun1.tpe.widen}, was ${fun.typeOpt.widen}")
+          }
       }
     }