SI-9540 typedFunction is erasure aware

When typer is running during erasure, must assign erased FunctionType
in typedFunction. This removes a bunch of unneeded casts now we no longer
assign a half-erased FunctionType.

I poked around a bit, and it looks like erasure doesn't want typer
to erase built-in types (like Unit/Any/Nothing).
They are already treated specially during erasure.

3 files changed, 13 insertions, 7 deletions

diff --git a/src/compiler/scala/tools/nsc/transform/Delambdafy.scala b/src/compiler/scala/tools/nsc/transform/Delambdafy.scala
index f15d05f7df..f7ec9391a7 100644
--- a/src/compiler/scala/tools/nsc/transform/Delambdafy.scala
+++ b/src/compiler/scala/tools/nsc/transform/Delambdafy.scala
@@ -127,9 +127,8 @@ abstract class Delambdafy extends Transform with TypingTransformers with ast.Tre
 
     // turns a lambda into a new class def, a New expression instantiating that class
     private def transformFunction(originalFunction: Function): TransformedFunction = {
-      val functionTpe = originalFunction.tpe
-      val targs = functionTpe.typeArgs
-      val formals :+ restpe = targs
+      val formals  = originalFunction.vparams.map(_.tpe)
+      val restpe   = originalFunction.body.tpe.deconst
       val oldClass = originalFunction.symbol.enclClass
 
       // find which variables are free in the lambda because those are captures that need to be
diff --git a/src/compiler/scala/tools/nsc/typechecker/Typers.scala b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
index 3a8edafd58..783db65b33 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Typers.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
@@ -128,6 +128,13 @@ trait Typers extends Adaptations with Tags with TypersTracking with PatternTyper
     def canTranslateEmptyListToNil    = true
     def missingSelectErrorTree(tree: Tree, qual: Tree, name: Name): Tree = tree
 
+    // when type checking during erasure, generate erased types in spots that aren't transformed by erasure
+    // (it erases in TypeTrees, but not in, e.g., the type a Function node)
+    def phasedAppliedType(sym: Symbol, args: List[Type]) = {
+      val tp = appliedType(sym, args)
+      if (phase.erasedTypes) erasure.specialScalaErasure(tp) else tp
+    }
+
     def typedDocDef(docDef: DocDef, mode: Mode, pt: Type): Tree =
       typed(docDef.definition, mode, pt)
 
@@ -2983,7 +2990,7 @@ trait Typers extends Adaptations with Tags with TypersTracking with PatternTyper
             val formals = vparamSyms map (_.tpe)
             val body1 = typed(fun.body, respt)
             val restpe = packedType(body1, fun.symbol).deconst.resultType
-            val funtpe  = appliedType(FunctionSymbol, formals :+ restpe: _*)
+            val funtpe  = phasedAppliedType(FunctionSymbol, formals :+ restpe)
 
             treeCopy.Function(fun, vparams, body1) setType funtpe
         }
@@ -3215,7 +3222,7 @@ trait Typers extends Adaptations with Tags with TypersTracking with PatternTyper
           // less expensive than including them in inferMethodAlternative (see below).
           def shapeType(arg: Tree): Type = arg match {
             case Function(vparams, body) =>
-              functionType(vparams map (_ => AnyTpe), shapeType(body))
+              functionType(vparams map (_ => AnyTpe), shapeType(body)) // TODO: should this be erased when retyping during erasure?
             case AssignOrNamedArg(Ident(name), rhs) =>
               NamedType(name, shapeType(rhs))
             case _ =>
diff --git a/test/files/run/delambdafy_t6028.check b/test/files/run/delambdafy_t6028.check
index c8c4b1cb4c..b5a6e4b64e 100644
--- a/test/files/run/delambdafy_t6028.check
+++ b/test/files/run/delambdafy_t6028.check
@@ -11,7 +11,7 @@ package <empty> {
     def foo(methodParam: String): Function0 = {
       val methodLocal: String = "";
       {
-        (() => T.this.$anonfun$1(methodParam, methodLocal)).$asInstanceOf[Function0]()
+        (() => T.this.$anonfun$1(methodParam, methodLocal))
       }
     };
     def bar(barParam: String): Object = {
@@ -21,7 +21,7 @@ package <empty> {
     def tryy(tryyParam: String): Function0 = {
       var tryyLocal: runtime.ObjectRef = scala.runtime.ObjectRef.create("");
       {
-        (() => T.this.$anonfun$2(tryyParam, tryyLocal)).$asInstanceOf[Function0]()
+        (() => T.this.$anonfun$2(tryyParam, tryyLocal))
       }
     };
     final <artifact> private[this] def $anonfun$1(methodParam$1: String, methodLocal$1: String): String = T.this.classParam.+(T.this.field()).+(methodParam$1).+(methodLocal$1);