Address comments and add tests

Author: EnzeXing

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

@@ -151,7 +151,7 @@ class Objects(using Context @constructorOnly):
     def hasVar(sym: Symbol)(using Heap.MutableData): Boolean = Heap.containsVal(this, sym)
 
     def initVal(field: Symbol, value: Value)(using Context, Heap.MutableData) = log("Initialize " + field.show + " = " + value + " for " + this, printer) {
-      assert(field.is(Flags.Param) || !field.is(Flags.Mutable), "Field is mutable: " + field.show)
+      assert((field.is(Flags.Param) && field.is(Flags.JavaDefined)) || !field.is(Flags.Mutable), "Field is mutable: " + field.show + ", class = " + klass)
       Heap.writeJoinVal(this, field, value)
     }
 
@@ -421,7 +421,7 @@ class Objects(using Context @constructorOnly):
       def hasVar(sym: Symbol)(using EnvMap.EnvMapMutableData): Boolean = EnvMap.containsVal(this, sym)
 
       def initVal(field: Symbol, value: Value)(using Context, EnvMap.EnvMapMutableData) = log("Initialize " + field.show + " = " + value + " for " + this, printer) {
-        assert(field.is(Flags.Param) || !field.is(Flags.Mutable), "Field is mutable: " + field.show)
+        assert((field.is(Flags.Param) && field.is(Flags.JavaDefined)) || !field.is(Flags.Mutable), "Field is mutable: " + field.show)
         EnvMap.writeJoinVal(this, field, value)
       }
 
@@ -1804,7 +1804,7 @@ class Objects(using Context @constructorOnly):
             val seqPats = pats.drop(selectors.length - 1)
             val toSeqRes = call(resToMatch, selectors.last, Nil, resultTp, superType = NoType, needResolve = true)
             val toSeqResTp = resultTp.memberInfo(selectors.last).finalResultType
-            evalSeqPatterns(toSeqRes, toSeqResTp, elemTp, seqPats)
+            evalSeqPatterns(toSeqRes, toSeqResTp, elemTp, seqPats) // passing elemTp to evalSeqPatterns that does not exist?
           end if
 
         else

tests/init-global/pos/unapplySeq.scala

@@ -0,0 +1,29 @@
+trait Node {
+  val prefix = 5
+  val child = Array(3)
+}
+
+class SpecialNode extends Node
+
+class Group extends Node
+
+class C extends Node
+
+object Elem {
+  def apply(prefix: Int, children: Int*) = new C
+  def unapplySeq(n: Node) = n match {
+    case _: SpecialNode | _: Group => None
+    case _                         => Some((n.prefix, n.child.toSeq))
+  }
+}
+
+object O {
+  def updateNode(node: Node): Node =
+    node match {
+      case Elem(prefix, children @ _*) =>
+        Elem(prefix, children: _*)
+      case other => other
+    }
+
+  val a = updateNode(new Group)
+}