Make some context bound evidence params tracked

Make context bound evidence params tracked if they have types with abstract type members.

Author: odersky

compiler/src/dotty/tools/dotc/core/Symbols.scala

@@ -312,7 +312,6 @@ object Symbols extends SymUtils {
      *  With the given setup, all such calls will give implicit-not found errors
      */
     final def symbol(implicit ev: DontUseSymbolOnSymbol): Nothing = unsupported("symbol")
-    type DontUseSymbolOnSymbol
 
     final def source(using Context): SourceFile = {
       def valid(src: SourceFile): SourceFile =
@@ -402,13 +401,12 @@ object Symbols extends SymUtils {
         flags: FlagSet = this.flags,
         info: Type = this.info,
         privateWithin: Symbol = this.privateWithin,
-        coord: Coord = NoCoord, // Can be `= owner.coord` once we bootstrap
-        compUnitInfo: CompilationUnitInfo | Null = null // Can be `= owner.associatedFile` once we bootstrap
+        coord: Coord = NoCoord, // Can be `= owner.coord` once we have new default args
+        compUnitInfo: CompilationUnitInfo | Null = null // Can be `= owner.compilationUnitInfo` once we have new default args
     ): Symbol = {
       val coord1 = if (coord == NoCoord) owner.coord else coord
       val compilationUnitInfo1 = if (compilationUnitInfo == null) owner.compilationUnitInfo else compilationUnitInfo
 
-
       if isClass then
         newClassSymbol(owner, name.asTypeName, flags, _ => info, privateWithin, coord1, compilationUnitInfo1)
       else
@@ -936,6 +934,8 @@ object Symbols extends SymUtils {
       case (x: Symbol) :: _ if x.isType => Some(xs.asInstanceOf[List[TypeSymbol]])
       case _ => None
 
+  type DontUseSymbolOnSymbol
+
 // ----- Locating predefined symbols ----------------------------------------
 
   def requiredPackage(path: PreName)(using Context): TermSymbol = {

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

@@ -1885,6 +1885,28 @@ class Namer { typer: Typer =>
     ddef.trailingParamss.foreach(completeParams)
     val paramSymss = normalizeIfConstructor(ddef.paramss.nestedMap(symbolOfTree), isConstructor)
     sym.setParamss(paramSymss)
+
+    /** We add `tracked` to context bound witnesses that have abstract type members */
+    def needsTracked(sym: Symbol, param: ValDef)(using Context) =
+      !sym.is(Tracked)
+      && param.hasAttachment(ContextBoundParam)
+      && sym.info.memberNames(abstractTypeNameFilter).nonEmpty
+
+    /** Set every context bound evidence parameter of a class to be tracked,
+     *  provided it has a type that has an abstract type member. Reset private and local flags
+     *  so that the parameter becomes a `val`.
+     */
+    def setTracked(param: ValDef): Unit =
+      val sym = symbolOfTree(param)
+      sym.maybeOwner.maybeOwner.infoOrCompleter match
+        case info: TempClassInfo if needsTracked(sym, param) =>
+          typr.println(i"set tracked $param, $sym: ${sym.info} containing ${sym.info.memberNames(abstractTypeNameFilter).toList}")
+          for acc <- info.decls.lookupAll(sym.name) if acc.is(ParamAccessor) do
+            acc.resetFlag(PrivateLocal)
+            acc.setFlag(Tracked)
+            sym.setFlag(Tracked)
+        case _ =>
+
     def wrapMethType(restpe: Type): Type =
       instantiateDependent(restpe, paramSymss)
       methodType(paramSymss, restpe, ddef.mods.is(JavaDefined))
@@ -1893,10 +1915,18 @@ class Namer { typer: Typer =>
       wrapMethType(addParamRefinements(restpe, paramSymss))
 
     if isConstructor then
+      if sym.isPrimaryConstructor && Feature.enabled(modularity) then
+        ddef.termParamss.foreach(_.foreach(setTracked))
       // set result type tree to unit, but take the current class as result type of the symbol
       typedAheadType(ddef.tpt, defn.UnitType)
       wrapMethType(effectiveResultType(sym, paramSymss))
     else if sym.isAllOf(Given | Method) && Feature.enabled(modularity) then
+      // set every context bound evidence parameter of a given companion method
+      // to be tracked, provided it has a type that has an abstract type member.
+      // Add refinements for all tracked parameters to the result type.
+      for params <- ddef.termParamss; param <- params do
+        val psym = symbolOfTree(param)
+        if needsTracked(psym, param) then psym.setFlag(Tracked)
       valOrDefDefSig(ddef, sym, paramSymss, wrapRefinedMethType)
     else
       valOrDefDefSig(ddef, sym, paramSymss, wrapMethType)

tests/pos/hylolib-cb/AnyCollection.scala

@@ -14,7 +14,7 @@ final class AnyCollection[Element] private (
 object AnyCollection {
 
   /** Creates an instance forwarding its operations to `base`. */
-  def apply[Base](using b: Collection[Base])(base: Base): AnyCollection[b.Element] =
+  def apply[Base: Collection as b](base: Base): AnyCollection[b.Element] =
     // NOTE: This evidence is redefined so the compiler won't report ambiguity between `intIsValue`
     // and `anyValueIsValue` when the method is called on a collection of `Int`s. None of these
     // choices is even correct! Note also that the ambiguity is suppressed if the constructor of
@@ -42,7 +42,7 @@ object AnyCollection {
 
 }
 
-given anyCollectionIsCollection[T](using tIsValue: Value[T]): Collection[AnyCollection[T]] with {
+given anyCollectionIsCollection[T: Value]: Collection[AnyCollection[T]] with {
 
   type Element = T
   type Position = AnyValue

tests/pos/hylolib-cb/Collection.scala

@@ -89,7 +89,7 @@ trait Collection[Self] {
 
 }
 
-extension [Self](self: Self)(using s: Collection[Self]) {
+extension [Self: Collection as s](self: Self) {
 
   /** Returns the first element of `self` along with a slice containing the suffix after this
     * element, or `None` if `self` is empty.
@@ -148,7 +148,7 @@ extension [Self](self: Self)(using s: Collection[Self]) {
     * @complexity
     *   O(n) where n is the number of elements in `self`.
     */
-  def map[T](using Value[T])(transform: (s.Element) => T): HyArray[T] =
+  def map[T: Value](transform: (s.Element) => T): HyArray[T] =
     self.reduce(
       HyArray[T](),
       (r, e) => r.append(transform(e), assumeUniqueness = true)
@@ -257,9 +257,8 @@ extension [Self](self: Self)(using s: Collection[Self]) {
 
 }
 
-extension [Self](self: Self)(using
-    s: Collection[Self],
-    e: Value[s.Element]
+extension [Self: Collection as s](self: Self)(using
+    Value[s.Element]
 ) {
 
   /** Returns `true` if `self` contains the same elements as `other`, in the same order. */

tests/pos/hylolib-cb/HyArray.scala

@@ -1,12 +1,11 @@
+//> using options -language:experimental.modularity -source future
 package hylo
 
 import java.util.Arrays
 import scala.collection.mutable
 
 /** An ordered, random-access collection. */
-final class HyArray[Element] private (using
-    elementIsValue: Value[Element]
-)(
+final class HyArray[Element: Value as elementIsCValue](
     private var _storage: scala.Array[AnyRef | Null] | Null,
     private var _count: Int // NOTE: where do I document private fields
 ) {
@@ -155,14 +154,14 @@ final class HyArray[Element] private (using
 object HyArray {
 
   /** Creates an array with the given `elements`. */
-  def apply[T](using t: Value[T])(elements: T*): HyArray[T] =
+  def apply[T: Value](elements: T*): HyArray[T] =
     var a = new HyArray[T](null, 0)
     for (e <- elements) a = a.append(e, assumeUniqueness = true)
     a
 
 }
 
-given hyArrayIsValue[T](using tIsValue: Value[T]): Value[HyArray[T]] with {
+given [T: Value] => Value[HyArray[T]] with {
 
   extension (self: HyArray[T]) {
 
@@ -179,7 +178,7 @@ given hyArrayIsValue[T](using tIsValue: Value[T]): Value[HyArray[T]] with {
 
 }
 
-given hyArrayIsCollection[T](using tIsValue: Value[T]): Collection[HyArray[T]] with {
+given [T: Value] => Collection[HyArray[T]] with {
 
   type Element = T
   type Position = Int

tests/pos/hylolib-cb/Slice.scala

@@ -1,9 +1,7 @@
 package hylo
 
 /** A view into a collection. */
-final class Slice[Base](using
-    val b: Collection[Base]
-)(
+final class Slice[Base: Collection as b](
     val base: Base,
     val bounds: Range[b.Position]
 ) {
@@ -26,7 +24,7 @@ final class Slice[Base](using
 
 }
 
-given sliceIsCollection[T](using c: Collection[T]): Collection[Slice[T]] with {
+given sliceIsCollection[T: Collection as c]: Collection[Slice[T]] with {
 
   type Element = c.Element
   type Position = c.Position