Run ExtensionMethods after TailRec

Author: allanrenucci

compiler/src/dotty/tools/dotc/Compiler.scala

@@ -65,10 +65,10 @@ class Compiler {
     List(new CheckStatic,            // Check restrictions that apply to @static members
          new ElimRepeated,           // Rewrite vararg parameters and arguments
          new NormalizeFlags,         // Rewrite some definition flags
-         new ExtensionMethods,       // Expand methods of value classes with extension methods
          new ExpandSAMs,             // Expand single abstract method closures to anonymous classes
          new ShortcutImplicits,      // Allow implicit functions without creating closures
          new TailRec,                // Rewrite tail recursion to loops
+         new ExtensionMethods,       // Expand methods of value classes with extension methods
          new ByNameClosures,         // Expand arguments to by-name parameters to closures
          new LiftTry,                // Put try expressions that might execute on non-empty stacks into their own methods
          new HoistSuperArgs,         // Hoist complex arguments of supercalls to enclosing scope

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

@@ -34,7 +34,7 @@ import SymUtils._
  * This is different from the implementation of value classes in Scala 2
  * (see SIP-15) which uses `asInstanceOf` which does not typecheck.
  *
- * Finally, if the constructor of a value class is private pr protected
+ * Finally, if the constructor of a value class is private or protected
  * it is widened to public.
  */
 class ExtensionMethods extends MiniPhase with DenotTransformer with FullParameterization { thisPhase =>
@@ -47,6 +47,7 @@ class ExtensionMethods extends MiniPhase with DenotTransformer with FullParamete
 
   override def runsAfter = Set(
     ElimRepeated.name,
+    TailRec.name,            // if ran before, tailrec reports spurious errors (original method is not tailrec anymore)
     ProtectedAccessors.name  // protected accessors cannot handle code that is moved from class to companion object
   )
 
@@ -111,12 +112,7 @@ class ExtensionMethods extends MiniPhase with DenotTransformer with FullParamete
           moduleClassSym
       }
     case ref: SymDenotation =>
-      if (isMethodWithExtension(ref.symbol) && ref.hasAnnotation(defn.TailrecAnnot)) {
-        val ref1 = ref.copySymDenotation()
-        ref1.removeAnnotation(defn.TailrecAnnot)
-        ref1
-      }
-      else if (ref.isConstructor && isDerivedValueClass(ref.owner) && ref.is(AccessFlags)) {
+      if (ref.isConstructor && isDerivedValueClass(ref.owner) && ref.is(AccessFlags)) {
         val ref1 = ref.copySymDenotation()
         ref1.resetFlag(AccessFlags)
         ref1
@@ -137,8 +133,7 @@ class ExtensionMethods extends MiniPhase with DenotTransformer with FullParamete
       (imeth.flags | Final) &~ (Override | Protected | AbsOverride),
       fullyParameterizedType(imeth.info, imeth.owner.asClass),
       privateWithin = imeth.privateWithin, coord = imeth.coord)
-    extensionMeth.addAnnotations(imeth.annotations)(ctx.withPhase(thisPhase))
-      // need to change phase to add tailrec annotation which gets removed from original method in the same phase.
+    extensionMeth.addAnnotations(imeth.annotations)
     extensionMeth
   }
 

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

@@ -68,7 +68,9 @@ class TailRec extends MiniPhase with FullParameterization {
 
   override def phaseName: String = TailRec.name
 
-  override def runsAfter = Set(ShortcutImplicits.name) // Replaces non-tail calls by tail calls
+  override def runsAfter = Set(
+    ShortcutImplicits.name // Replaces non-tail calls by tail calls
+  )
 
   final val labelFlags = Flags.Synthetic | Flags.Label
 
@@ -144,7 +146,8 @@ class TailRec extends MiniPhase with FullParameterization {
                   else ref(label).appliedToTypes(dd.tparams.map(_.tpe))
                 ).appliedToArgss(vparamss0.map(_.map(x=> ref(x.symbol))))
               Block(List(labelDef), callIntoLabel)
-          }} else {
+            }
+          } else {
             if (mandatory) ctx.error(
               "TailRec optimisation not applicable, method not tail recursive",
               // FIXME: want to report this error on `dd.namePos`, but

tests/run/value-classes-tailrec.scala

@@ -0,0 +1,11 @@
+class VCInt(val v: Int) extends AnyVal {
+  @annotation.tailrec final def tailCall: Boolean =
+    if (v > 0) new VCInt(v - 1).tailCall
+    else true
+}
+
+object Test {
+  def main(args: Array[String]): Unit = {
+    assert(new VCInt(10).tailCall)
+  }
+}