Fix #5924: don't move static fields to interfaces

Author: liufengyun

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

@@ -36,8 +36,6 @@ class LazyVals extends MiniPhase with IdentityDenotTransformer {
 
   override def changesMembers: Boolean = true  // the phase adds lazy val accessors
 
-  def transformer: LazyVals = new LazyVals
-
   val containerFlags: FlagSet = Synthetic | Mutable | Lazy
   val initFlags: FlagSet      = Synthetic | Method
 

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

@@ -24,7 +24,8 @@ class MoveStatics extends MiniPhase with SymTransformer {
   override def phaseName: String = MoveStatics.name
 
   def transformSym(sym: SymDenotation)(implicit ctx: Context): SymDenotation = {
-    if (sym.hasAnnotation(defn.ScalaStaticAnnot) && sym.owner.is(Flags.Module) && sym.owner.companionClass.exists) {
+    if (sym.hasAnnotation(defn.ScalaStaticAnnot) && sym.owner.is(Flags.Module) &&
+        sym.owner.companionClass.exists && !sym.owner.companionClass.is(Flags.Trait)) {
       sym.owner.asClass.delete(sym.symbol)
       sym.owner.companionClass.asClass.enter(sym.symbol)
       val flags = if (sym.is(Flags.Method)) sym.flags else sym.flags | Flags.Mutable
@@ -60,9 +61,10 @@ class MoveStatics extends MiniPhase with SymTransformer {
       def move(module: TypeDef, companion: TypeDef): List[Tree] = {
         assert(companion ne module)
         if (!module.symbol.is(Flags.Module)) move(companion, module)
+        else if (companion != null && companion.symbol.is(Flags.Trait)) List(module, companion)
         else {
           val allMembers =
-            (if(companion ne null) {companion.rhs.asInstanceOf[Template].body} else Nil) ++
+            (if(companion != null) {companion.rhs.asInstanceOf[Template].body} else Nil) ++
             module.rhs.asInstanceOf[Template].body
           val (newModuleBody, newCompanionBody) = allMembers.partition(x => {assert(x.symbol.exists); x.symbol.owner == module.symbol})
           Trees.flatten(rebuild(companion, newCompanionBody) :: rebuild(module, newModuleBody) :: Nil)

tests/run/i5924.scala

@@ -0,0 +1,9 @@
+trait Matchers {
+  object Helper
+}
+
+object Matchers extends Matchers
+
+object Test {
+  def main(args: Array[String]): Unit = Matchers
+}