SIP 61 - remove tasty hack by not "telescoping" forwarders

Now, all forwarders directly call the unrolled method.
This means that there is no need to resolve an invisible method,
so the "hack" using TERMREFdirect is no longer needed.

This increases bytecode size but reduces stack depth.

Also removed scala.annotation.internal.UnrolledForwarder,
as it is only needed for the TASTy hack.

Author: bishabosha

compiler/src/dotty/tools/dotc/core/Definitions.scala

@@ -1040,7 +1040,6 @@ class Definitions {
   @tu lazy val NowarnAnnot: ClassSymbol = requiredClass("scala.annotation.nowarn")
   @tu lazy val UnusedAnnot: ClassSymbol = requiredClass("scala.annotation.unused")
   @tu lazy val UnrollAnnot: ClassSymbol = requiredClass("scala.annotation.unroll")
-  @tu lazy val UnrollForwarderAnnot: ClassSymbol = requiredClass("scala.annotation.internal.UnrollForwarder")
   @tu lazy val TransparentTraitAnnot: ClassSymbol = requiredClass("scala.annotation.transparentTrait")
   @tu lazy val NativeAnnot: ClassSymbol = requiredClass("scala.native")
   @tu lazy val RepeatedAnnot: ClassSymbol = requiredClass("scala.annotation.internal.Repeated")

compiler/src/dotty/tools/dotc/core/tasty/TreePickler.scala

@@ -490,9 +490,6 @@ class TreePickler(pickler: TastyPickler, attributes: Attributes) {
                   writeByte(if name.isTypeName then SELECTtpt else SELECT)
                   pickleNameAndSig(name, sig, ename)
                   pickleTree(qual)
-                else if sym.is(Invisible) && qual.isInstanceOf[This] && sym.hasAnnotation(defn.UnrollForwarderAnnot) then
-                  writeByte(TERMREFdirect)
-                  pickleSymRef(sym) // SIP-61 HACK: resolution from Signature filters out Invisible symbols
                 else // select from owner
                   writeByte(SELECTin)
                   withLength {

compiler/src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala

@@ -1259,12 +1259,7 @@ class TreeUnpickler(reader: TastyReader,
         goto(start)
         readType() match {
           case path: TypeRef => TypeTree(path)
-          case path: TermRef =>
-            val sym = path.symbol
-            if sym.is(Invisible) && sym.hasAnnotation(defn.UnrollForwarderAnnot) then
-              This(sym.owner.asClass).select(sym)
-            else
-              ref(path)
+          case path: TermRef => ref(path)
           case path: ThisType => untpd.This(untpd.EmptyTypeIdent).withType(path)
           case path: ConstantType => Literal(path.value)
           case path: ErrorType if isBestEffortTasty => TypeTree(path)

compiler/src/dotty/tools/dotc/transform/UnrollDefinitions.scala

@@ -116,6 +116,7 @@ class UnrollDefinitions extends MacroTransform, IdentityDenotTransformer {
   def generateSingleForwarder(defdef: DefDef,
                               prevMethodType: Type,
                               paramIndex: Int,
+                              paramCount: Int,
                               nextParamIndex: Int,
                               nextSymbol: Symbol,
                               annotatedParamListIndex: Int,
@@ -125,18 +126,12 @@ class UnrollDefinitions extends MacroTransform, IdentityDenotTransformer {
       val forwarderDefSymbol0 = Symbols.newSymbol(
         defdef.symbol.owner,
         defdef.name,
-        (defdef.symbol.flags &~
-        HasDefaultParams &~
-        (if nextParamIndex == -1 then EmptyFlags else Deferred)) |
+        defdef.symbol.flags &~ HasDefaultParams |
         Invisible | Synthetic,
         NoType, // fill in later
         coord = nextSymbol.span.shift(1) // shift by 1 to avoid "secondary constructor must call preceding" error
       ).entered
 
-      // we need this such that when unpickling a TERMREFdirect, if we see this annotation,
-      // we restore the tree to a Select
-      forwarderDefSymbol0.addAnnotation(defn.UnrollForwarderAnnot)
-
       val newParamSymMappings = extractParamSymss(copyParamSym(_, forwarderDefSymbol0))
       val (oldParams, newParams) = newParamSymMappings.flatten.unzip
 
@@ -170,7 +165,7 @@ class UnrollDefinitions extends MacroTransform, IdentityDenotTransformer {
         .map(_.size)
         .sum
 
-      val defaultCalls = Range(paramIndex, nextParamIndex).map(n =>
+      val defaultCalls = Range(paramIndex, paramCount).map(n =>
 
         def makeSelect(refTree: Tree, name: TermName): Tree =
           val sym = refTree.symbol
@@ -204,7 +199,8 @@ class UnrollDefinitions extends MacroTransform, IdentityDenotTransformer {
             else Apply(lhs, newParams)
       )
 
-      val forwarderInner: Tree = This(defdef.symbol.owner.asClass).select(nextSymbol)
+      val forwarderInner: Tree =
+        This(defdef.symbol.owner.asClass).select(defdef.symbol)
 
       val forwarderCallArgs =
         newParamSymLists.zipWithIndex.map{case (ps, i) =>
@@ -226,8 +222,7 @@ class UnrollDefinitions extends MacroTransform, IdentityDenotTransformer {
     }
 
     val forwarderDef =
-      tpd.DefDef(forwarderDefSymbol,
-        rhs = if nextParamIndex == -1 then EmptyTree else forwarderRhs())
+      tpd.DefDef(forwarderDefSymbol, rhs = forwarderRhs())
 
     forwarderDef.withSpan(nextSymbol.span.shift(1))
   }
@@ -297,6 +292,7 @@ class UnrollDefinitions extends MacroTransform, IdentityDenotTransformer {
                     defdef,
                     defdef.symbol.info,
                     paramIndex,
+                    paramCount,
                     nextParamIndex,
                     nextSymbol,
                     paramClauseIndex,

library/src/scala/annotation/internal/UnrollForwarder.scala

@@ -0,0 +1,72 @@
+//> using options -experimental
+
+import scala.annotation.unroll
+import scala.deriving.Mirror
+
+class Unrolled {
+  final def foo(
+    s: String,
+    @unroll y: Boolean = true,
+    @unroll i: Int = 0,
+    @unroll c: Char = '?'): String = s + y + i + c
+}
+
+class Outer {
+  class Unrolled {
+    final def bar(
+      s: String,
+      @unroll y: Boolean = true,
+      @unroll i: Int = 0,
+      @unroll c: Char = '?'): String = s + y + i + c
+  }
+
+  case class UnrolledCase(
+    s: String,
+    @unroll y: Boolean = true,
+    @unroll i: Int = 0,
+    @unroll c: Char = '?') {
+    def baz: String = s + y + i + c
+  }
+
+  class UnrolledSecondary {
+    private var msg = ""
+
+    def qux: String = msg
+
+    def this(
+      s: String,
+      @unroll y: Boolean = true,
+      @unroll i: Int = 0,
+      @unroll c: Char = '?') = {
+      this()
+      msg = s + y + i + c
+    }
+  }
+}
+
+@main def Test: Unit =
+  assert(Unrolled().foo("foo") == "footrue0?")
+  assert(Unrolled().foo("foo", false) == "foofalse0?")
+  assert(Unrolled().foo("foo", false, 1) == "foofalse1?")
+  assert(Unrolled().foo("foo", false, 1, '@') == "foofalse1@")
+  val outer = new Outer()
+  assert(new outer.Unrolled().bar("bar") == "bartrue0?")
+  assert(new outer.Unrolled().bar("bar", false) == "barfalse0?")
+  assert(new outer.Unrolled().bar("bar", false, 1) == "barfalse1?")
+  assert(new outer.Unrolled().bar("bar", false, 1, '@') == "barfalse1@")
+  assert(outer.UnrolledCase.apply("baz").baz == "baztrue0?")
+  assert(outer.UnrolledCase.apply("baz", false).baz == "bazfalse0?")
+  assert(outer.UnrolledCase.apply("baz", false, 1).baz == "bazfalse1?")
+  assert(outer.UnrolledCase.apply("baz", false, 1, '@').baz == "bazfalse1@")
+  assert((new outer.UnrolledCase("baz")).baz == "baztrue0?")
+  assert((new outer.UnrolledCase("baz", false)).baz == "bazfalse0?")
+  assert((new outer.UnrolledCase("baz", false, 1)).baz == "bazfalse1?")
+  assert((new outer.UnrolledCase("baz", false, 1, '@')).baz == "bazfalse1@")
+  assert(summon[Mirror.Of[outer.UnrolledCase]].fromProduct(Tuple("baz")).baz == "baztrue0?")
+  assert(summon[Mirror.Of[outer.UnrolledCase]].fromProduct(("baz", false)).baz == "bazfalse0?")
+  assert(summon[Mirror.Of[outer.UnrolledCase]].fromProduct(("baz", false, 1)).baz == "bazfalse1?")
+  assert(summon[Mirror.Of[outer.UnrolledCase]].fromProduct(("baz", false, 1, '@')).baz == "bazfalse1@")
+  assert(new outer.UnrolledSecondary("qux").qux == "quxtrue0?")
+  assert(new outer.UnrolledSecondary("qux", false).qux == "quxfalse0?")
+  assert(new outer.UnrolledSecondary("qux", false, 1).qux == "quxfalse1?")
+  assert(new outer.UnrolledSecondary("qux", false, 1, '@').qux == "quxfalse1@")