Handle outers of trait as the same in concrete semantics

For traits, its outers will be proxy methods of the class that extends
the trait. As the prefix is stable and is a valid value before any
super constructor calls. Therefore, we may think the outers for traits
are immediately set following the class parameters.

Also, when trying promotion of warm values, we never try warm values
whose fields are not fully filled -- which corresponds to promote
ThisRef with non-initialized fields, and errors will be reported when
the class is checked separately.

Author: liufengyun

compiler/src/dotty/tools/dotc/transform/init/Objects.scala

@@ -135,12 +135,13 @@ class Objects {
     def instantiate(klass: ClassSymbol, ctor: Symbol, args: List[Value], source: Tree): Contextual[Result] =
       value.instantiate(klass, ctor, args, source) ++ errors
 
-    def ensureAccess(klass: ClassSymbol, source: Tree): Contextual[Result] =
+    def ensureAccess(klass: ClassSymbol, source: Tree): Contextual[Result] = log("ensure access " + value.show, printer) {
       value match
       case obj: ObjectRef =>
         if obj.klass == klass then this
         else obj.access(source) ++ errors
       case _ => this
+    }
   }
 
   /** The state that threads through the interpreter */
@@ -233,7 +234,7 @@ class Objects {
             eval(rhs, addr, target.owner.asClass, cacheResult = true)
           else
             given Trace = trace1
-            val obj = if heap.contains(addr) then heap(addr) else Objekt(addr.klass, mutable.Map.empty, mutable.Map.empty)
+            val obj = heap(addr)
             if obj.fields.contains(target) then
               Result(obj.fields(target), Nil)
             else if target.is(Flags.ParamAccessor) then
@@ -658,7 +659,7 @@ class Objects {
   }
 
   /** Resolve C.this that appear in `klass` */
-  def resolveThis(target: ClassSymbol, thisV: Value, klass: ClassSymbol, source: Tree, elideObjectAccess: Boolean = false): Contextual[Result] = log("resolving " + target.show + ", this = " + thisV.show + " in " + klass.show, printer, res => res.asInstanceOf[Value].show) {
+  def resolveThis(target: ClassSymbol, thisV: Value, klass: ClassSymbol, source: Tree, elideObjectAccess: Boolean = false): Contextual[Result] = log("resolving " + target.show + ", this = " + thisV.show + " in " + klass.show, printer, res => res.asInstanceOf[Result].show) {
     if target == klass then Result(thisV, Nil)
     else if target.is(Flags.Package) then Result(Bottom, Nil)
     else if target.isStaticObjectRef then
@@ -699,7 +700,8 @@ class Objects {
 
     val paramsMap = tpl.constr.termParamss.flatten.map(vdef => vdef.name -> vdef.symbol).toMap
 
-    def superCall(tref: TypeRef, ctor: Symbol, args: List[Value], source: Tree): Unit =
+    type Handler = (() => Unit) => Unit
+    def superCall(tref: TypeRef, ctor: Symbol, args: List[Value], source: Tree, handler: Handler): Unit =
       val cls = tref.classSymbol.asClass
       // update outer for super class
       val res = outerValue(tref, thisV, klass, source)
@@ -708,53 +710,57 @@ class Objects {
 
       // follow constructor
       if cls.hasSource then
-        use(trace.add(source)) {
-          val res2 = thisV.call(ctor, args, superType = NoType, source)
-          errorBuffer ++= res2.errors
+        handler { () =>
+          use(trace.add(source)) {
+            val res2 = thisV.call(ctor, args, superType = NoType, source)
+            errorBuffer ++= res2.errors
+          }
         }
+      else
+        handler { () => () }
 
     // parents
-    def initParent(parent: Tree) = parent match {
+    def initParent(parent: Tree, handler: Handler) = parent match {
       case tree @ Block(stats, NewExpr(tref, New(tpt), ctor, argss)) =>  // can happen
         eval(stats, thisV, klass).foreach { res => errorBuffer ++= res.errors }
         val resArgs = evalArgs(argss.flatten, thisV, klass)
         val argsValues = resArgs.map(_.value)
         val argsErrors = resArgs.flatMap(_.errors)
 
         errorBuffer ++= argsErrors
-        superCall(tref, ctor, argsValues, tree)
+        superCall(tref, ctor, argsValues, tree, handler)
 
       case tree @ NewExpr(tref, New(tpt), ctor, argss) =>       // extends A(args)
         val resArgs = evalArgs(argss.flatten, thisV, klass)
         val argsValues = resArgs.map(_.value)
         val argsErrors = resArgs.flatMap(_.errors)
 
         errorBuffer ++= argsErrors
-        superCall(tref, ctor, argsValues, tree)
+        superCall(tref, ctor, argsValues, tree, handler)
 
       case _ =>   // extends A or extends A[T]
         val tref = typeRefOf(parent.tpe)
-        superCall(tref, tref.classSymbol.primaryConstructor, Nil, parent)
+        superCall(tref, tref.classSymbol.primaryConstructor, Nil, parent, handler)
     }
 
     // see spec 5.1 about "Template Evaluation".
     // https://www.scala-lang.org/files/archive/spec/2.13/05-classes-and-objects.html
     if !klass.is(Flags.Trait) then
+      // outers are set first
+      val tasks = new mutable.ArrayBuffer[() => Unit]
+      val handler: Handler = task => tasks.append(task)
+
       // 1. first init parent class recursively
       // 2. initialize traits according to linearization order
       val superParent = tpl.parents.head
       val superCls = superParent.tpe.classSymbol.asClass
-      initParent(superParent)
-
-      // Access to the object possible after this point
-      if klass.isStaticOwner then
-        thisV.updateField(klass, thisV)
+      initParent(superParent, handler)
 
       val parents = tpl.parents.tail
       val mixins = klass.baseClasses.tail.takeWhile(_ != superCls)
       mixins.reverse.foreach { mixin =>
         parents.find(_.tpe.classSymbol == mixin) match
-        case Some(parent) => initParent(parent)
+        case Some(parent) => initParent(parent, handler)
         case None =>
           // According to the language spec, if the mixin trait requires
           // arguments, then the class must provide arguments to it explicitly
@@ -765,9 +771,21 @@ class Objects {
           // term arguments to B. That can only be done in a concrete class.
           val tref = typeRefOf(klass.typeRef.baseType(mixin).typeConstructor)
           val ctor = tref.classSymbol.primaryConstructor
-          if ctor.exists then superCall(tref, ctor, Nil, superParent)
+          if ctor.exists then superCall(tref, ctor, Nil, superParent, handler)
       }
 
+      // initialize super classes after outers are set
+      // 1. first call super class constructor
+      // 2. make the object accessible
+      // 3. call mixin initializations
+      tasks.head()
+
+      // Access to the object possible after this point
+      if klass.isStaticOwner then
+        thisV.updateField(klass, thisV)
+
+      tasks.tail.foreach(task => task())
+
 
     // class body
     tpl.body.foreach {