Check of cyclic object initialization v4

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

@@ -71,7 +71,7 @@ class TreeChecker extends Phase with SymTransformer {
 
     if (sym.isClass && !sym.isAbsent()) {
       val validSuperclass = sym.isPrimitiveValueClass || defn.syntheticCoreClasses.contains(sym) ||
-        (sym eq defn.ObjectClass) || sym.isOneOf(NoSuperClassFlags) || (sym.asClass.superClass.exists) ||
+        (sym eq defn.ObjectClass) || sym.isOneOf(NoSuperClassFlags) || (!sym.isCompleted || sym.asClass.superClass.exists) ||
         sym.isRefinementClass
 
       assert(validSuperclass, i"$sym has no superclass set")

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

@@ -24,6 +24,7 @@ class Checker extends MiniPhase {
   val phaseName = "initChecker"
 
   private val semantic = new Semantic
+  private val objects = new Objects
 
   override val runsAfter = Set(Pickler.name)
 
@@ -55,6 +56,9 @@ class Checker extends MiniPhase {
       heap.update(thisRef, obj)
       val res = eval(tpl, thisRef, cls)
       res.errors.foreach(_.issue)
+
+      if objects.isStaticObjectRef(cls) then
+        objects.check(cls)
     }
 
     tree

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

@@ -84,7 +84,7 @@ object Errors {
 
   case class CallUnknown(meth: Symbol, source: Tree, trace: Seq[Tree]) extends Error {
     def show(using Context): String =
-      val prefix = if meth.is(Flags.Method) then "Calling the external method " else "Accessing the external field"
+      val prefix = if meth.is(Flags.Method) then "Calling the external " else "Accessing the external "
       prefix + meth.show + " may cause initialization errors" + "."
   }
 
@@ -105,4 +105,21 @@ object Errors {
         }.mkString)
     }
   }
+
+  case class CyclicObjectInit(objs: Seq[Symbol], trace: Seq[Tree]) extends Error {
+    def source: Tree = trace.last
+    def show(using Context): String =
+      "Cyclic object initialization for " + objs.map(_.show).mkString(", ") + "."
+
+    override def issue(using Context): Unit =
+      report.warning(show + stacktrace, objs.head.srcPos)
+  }
+
+  case class ObjectNotInit(obj: Symbol, trace: Seq[Tree]) extends Error {
+    def source: Tree = trace.last
+    def show(using Context): String = obj.show + " not yet initialized " + "."
+
+    override def issue(using Context): Unit =
+      report.warning(show + stacktrace, obj.srcPos)
+  }
 }