Experiment with declaration site tracked

compiler/src/dotty/tools/dotc/ast/Desugar.scala

@@ -1577,6 +1577,8 @@ object desugar {
     case valdef @ ValDef(_, _, _) =>
       val sym = valdef.symbol
       !ctx.owner.exists || ctx.owner.isClass || ctx.owner.is(Case) || ctx.owner.isConstructor || valdef.mods.is(Param) || valdef.mods.is(ParamAccessor)
+    case typeDef: TypeDef if typeDef.isClassDef =>
+      true
   }
 
   def checkOpaqueAlias(tree: MemberDef)(using Context): MemberDef =

compiler/src/dotty/tools/dotc/typer/Namer.scala

@@ -2073,7 +2073,7 @@ class Namer { typer: Typer =>
     val sym = symbolOfTree(param)
     sym.maybeOwner.maybeOwner.infoOrCompleter match
       case info: ClassInfo
-        if !sym.is(Tracked) && isContextBoundWitnessWithAbstractMembers(sym, param, sym.maybeOwner.maybeOwner) =>
+        if !sym.is(Tracked) && (sym.info.widen.typeSymbol.is(Tracked) || isContextBoundWitnessWithAbstractMembers(sym, param, sym.maybeOwner.maybeOwner)) =>
         typr.println(i"set tracked $param, $sym: ${sym.info} containing ${sym.info.memberNames(abstractTypeNameFilter).toList}")
         setParamTrackedWithAccessors(sym, info)
       case _ =>

tests/neg/abstract-tracked.check

@@ -1,15 +1,7 @@
--- [E156] Syntax Error: tests/neg/abstract-tracked.scala:4:14 ----------------------------------------------------------
-4 |tracked trait F // error
-  |^^^^^^^^^^^^^^^
-  |Modifier tracked is not allowed for this definition
 -- [E156] Syntax Error: tests/neg/abstract-tracked.scala:9:15 ----------------------------------------------------------
 9 |tracked object O // error
   |^^^^^^^^^^^^^^^^
   |Modifier tracked is not allowed for this definition
--- [E156] Syntax Error: tests/neg/abstract-tracked.scala:11:14 ---------------------------------------------------------
-11 |tracked class C // error
-   |^^^^^^^^^^^^^^^
-   |Modifier tracked is not allowed for this definition
 -- [E156] Syntax Error: tests/neg/abstract-tracked.scala:7:14 ----------------------------------------------------------
 7 |  tracked def f: F // error
   |  ^^^^^^^^^^^^^^^^

tests/neg/abstract-tracked.scala

@@ -1,14 +1,14 @@
 import scala.language.experimental.modularity
 import scala.language.future
 
-tracked trait F // error
+tracked trait F
 
 trait G:
   tracked def f: F // error
 
 tracked object O // error
 
-tracked class C // error
+tracked class C
 
 def f =
   tracked val x = 1 // error

tests/neg/tracked.check

@@ -22,10 +22,6 @@
 11 |  tracked object Foo // error
    |  ^^^^^^^^^^^^^^^^^^
    |  Modifier tracked is not allowed for this definition
--- [E156] Syntax Error: tests/neg/tracked.scala:14:16 ------------------------------------------------------------------
-14 |  tracked class D // error
-   |  ^^^^^^^^^^^^^^^
-   |  Modifier tracked is not allowed for this definition
 -- [E156] Syntax Error: tests/neg/tracked.scala:17:15 ------------------------------------------------------------------
 17 |  tracked type T = Int // error
    |  ^^^^^^^^^^^^^^^^^^^^

tests/neg/tracked.scala

@@ -11,7 +11,7 @@ object B:
   tracked object Foo // error
 
 object C:
-  tracked class D // error
+  tracked class D
 
 object D:
   tracked type T = Int // error

tests/pos/definition-site-tracked.scala

@@ -0,0 +1,25 @@
+import scala.language.experimental.modularity
+
+tracked trait Show[Self]:
+  type Out
+  def show(self: Self): Out
+
+given ShowPerson: Show[Person] with
+  type Out = Int
+  def show(self: Person): Int = self.name.length
+
+class Person(val name: String)(val showW: Show[Person]):
+  def show = showW.show(this)
+
+given ShowString: Show[String] with
+  type Out = Double
+  def show(self: String): Double = self.length.toDouble
+
+class Person1[S <: Show[String]](val name: String)(val showW: S):
+  def show = showW.show(name)
+
+def Test =
+  val kasia = Person("Kasia")(ShowPerson)
+  val _: Int = kasia.show
+  val kasia1 = Person1("Kasia")(ShowString)
+  val _: Double = kasia1.show