Represent all retains annotations as CompactAnnotations

Author: odersky

compiler/src/dotty/tools/dotc/cc/CaptureOps.scala

@@ -14,7 +14,7 @@ import Annotations.Annotation
 import CaptureSet.VarState
 import Capabilities.*
 import Mutability.isStatefulType
-import StdNames.nme
+import StdNames.{nme, tpnme}
 import config.Feature
 import NameKinds.TryOwnerName
 import typer.ProtoTypes.WildcardSelectionProto
@@ -545,13 +545,23 @@ extension (cls: ClassSymbol)
 
 extension (sym: Symbol)
 
-  /** This symbol is one of `retains` or `retainsCap` */
+  private def inScalaAnnotation(using Context): Boolean =
+    sym.maybeOwner.name == tpnme.annotation
+    && sym.owner.owner == defn.ScalaPackageClass
+
+  /** Is this symbol one of `retains` or `retainsCap`?
+   *  Try to avoid cycles by not forcing definition symbols except scala package.
+   */
   def isRetains(using Context): Boolean =
-    sym == defn.RetainsAnnot || sym == defn.RetainsCapAnnot
+    (sym.name == tpnme.retains || sym.name == tpnme.retainsCap)
+    && inScalaAnnotation
 
-  /** This symbol is one of `retains`, `retainsCap`, or`retainsByName` */
+  /** Is this symbol one of `retains`, `retainsCap`, or`retainsByName`?
+   *  Try to avoid cycles by not forcing definition symbols except scala package.
+   */
   def isRetainsLike(using Context): Boolean =
-    isRetains || sym == defn.RetainsByNameAnnot
+    (sym.name == tpnme.retains || sym.name == tpnme.retainsCap || sym.name == tpnme.retainsByName)
+    && inScalaAnnotation
 
   /** A class is pure if:
    *   - one its base types has an explicitly declared self type with an empty capture set
@@ -658,7 +668,8 @@ class PathSelectionProto(val select: Select, val pt: Type) extends typer.ProtoTy
   def selector(using Context): Symbol = select.symbol
 
 /** Drop retains annotations in the inferred type if CC is not enabled
- *  or transform them into RetainingTypes if CC is enabled.
+ *  or transform them into RetainingTypes with Nothing as argument if CC is enabled
+ *  (we need to do that to keep by-name status).
  */
 class CleanupRetains(using Context) extends TypeMap:
   def apply(tp: Type): Type = tp match

compiler/src/dotty/tools/dotc/cc/CaptureSet.scala

@@ -536,10 +536,6 @@ sealed abstract class CaptureSet extends Showable:
   /** More info enabled by -Y flags */
   def optionalInfo(using Context): String = ""
 
-  /** A regular @retains or @retainsByName annotation with the elements of this set as arguments. */
-  def toRegularAnnotation(cls: Symbol)(using Context): Annotation =
-    Annotation(CaptureAnnotation(this, boxed = false)(cls).tree)
-
   override def toText(printer: Printer): Text =
     printer.toTextCaptureSet(this) ~~ description
 

compiler/src/dotty/tools/dotc/cc/RetainingType.scala

@@ -5,7 +5,7 @@ package cc
 import core.*
 import Types.*, Symbols.*, Contexts.*
 import ast.tpd.*
-import Annotations.Annotation
+import Annotations.CompactAnnotation
 import Decorators.i
 
 /** A builder and extractor for annotated types with @retains or @retainsByName annotations
@@ -15,8 +15,7 @@ object RetainingType:
 
   def apply(tp: Type, typeElems: Type, byName: Boolean = false)(using Context): Type =
     val annotCls = if byName then defn.RetainsByNameAnnot else defn.RetainsAnnot
-    val annotTree = New(AppliedType(annotCls.typeRef, typeElems :: Nil), Nil)
-    AnnotatedType(tp, Annotation(annotTree))
+    AnnotatedType(tp, CompactAnnotation(annotCls.typeRef.appliedTo(typeElems)))
 
   def unapply(tp: AnnotatedType)(using Context): Option[(Type, Type)] =
     val sym = tp.annot.symbol

compiler/src/dotty/tools/dotc/cc/ccConfig.scala

@@ -59,7 +59,7 @@ object ccConfig:
 
   /** Not used currently. Handy for trying out new features */
   def newScheme(using ctx: Context): Boolean =
-    Feature.sourceVersion.stable.isAtLeast(SourceVersion.`3.9`)
+    Feature.sourceVersion.stable.isAtLeast(SourceVersion.`3.7`)
 
   def allowUse(using Context): Boolean =
     Feature.sourceVersion.stable.isAtMost(SourceVersion.`3.7`)

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

@@ -66,32 +66,8 @@ object Annotations {
     def mapWith(tm: TypeMap)(using Context): Annotation =
       tpd.allArguments(tree) match
         case Nil => this
-
         case arg :: Nil if symbol.isRetainsLike =>
-          // Use a more efficient scheme to map retains and retainsByName annotations:
-          //  1. Map the type argument to a simple TypeTree instead of tree-mapping
-          //     the original tree. TODO Try to use this scheme for other annotations that
-          //     take only type arguments as well. We should wait until after 3.9 LTS to
-          //     do this, though.
-          //  2. Sanitize the arguments to prevent compilation time blowup.
-          //  3. Drop the annotation entirely if CC is not enabled somewhere.
-
-          def rebuild(tree: Tree, mappedType: Type): Tree = tree match
-            case Apply(fn, Nil) => cpy.Apply(tree)(rebuild(fn, mappedType), Nil)
-            case TypeApply(fn, arg :: Nil) => cpy.TypeApply(tree)(fn, TypeTree(mappedType) :: Nil)
-            case Block(Nil, expr) => rebuild(expr, mappedType)
-
-          if !Feature.ccEnabledSomewhere then
-            EmptyAnnotation // strip retains-like annotations unless capture checking is enabled
-          else
-            val mappedType = sanitize(tm(arg.tpe))
-            if mappedType `eql` arg.tpe then
-              this
-            else if cc.ccConfig.newScheme then
-              CompactAnnotation(symbol.typeRef.appliedTo(mappedType))
-            else
-              derivedAnnotation(rebuild(tree, mappedType))
-
+          assert(false, s"unexpected symbol $symbol for ConcreteAnnotation $this in ${ctx.source}, this should be a CompactAnnotation")
         case args =>
           // Checks if `tm` would result in any change by applying it to types
           // inside the annotations' arguments and checking if the resulting types
@@ -184,17 +160,35 @@ object Annotations {
         case ConstantType(c) => Some(c)
         case _ => None
 
+    /** Sanitize @retains arguments to approximate illegal types that could cause a compilation
+     *  time blowup before they are dropped ot detected. This means mapping all all skolems
+     *  (?n: T) to (?n: Any), and mapping all recursive captures that are not on CapSet to `^`.
+     *  Skolems and capturing types on types other than CapSet are not allowed in a
+     *  @retains annotation anyway, so the underlying type does not matter as long as it is also
+     *  illegal. See i24556.scala and i24556a.scala.
+     */
+    private def sanitize(tp: Type)(using Context): Type = tp match
+      case SkolemType(_) =>
+        SkolemType(defn.AnyType)
+      case tp @ AnnotatedType(parent, ann)
+      if ann.symbol.isRetainsLike && parent.typeSymbol != defn.Caps_CapSet =>
+        tp.derivedAnnotatedType(parent, ann.derivedClassAnnotation(defn.RetainsCapAnnot))
+      case tp @ OrType(tp1, tp2) =>
+        tp.derivedOrType(sanitize(tp1), sanitize(tp2))
+      case _ =>
+        tp
+
     override def mapWith(tm: TypeMap)(using Context): Annotation =
-      def derived(tp: Type) =
-        if tm.isRange(tp) then EmptyAnnotation else derivedAnnotation(tp)
-      def sanitizeArg(tp: Type) = tp match
-        case tp @ AppliedType(tycon, args) =>
-          tp.derivedAppliedType(tycon, args.mapConserve(sanitize))
+      val isRetains = symbol.isRetainsLike
+      if isRetains && !Feature.ccEnabledSomewhere then EmptyAnnotation
+      else tm(tp) match
+        case tp1 @ AppliedType(tycon, args) =>
+          val args1 = if isRetains then args.mapConserve(sanitize) else args
+          derivedAnnotation(tp1.derivedAppliedType(tycon, args1))
+        case tp1: TypeRef =>
+          derivedAnnotation(tp1)
         case _ =>
-          tp
-      if !symbol.isRetainsLike then derived(tm(tp))
-      else if Feature.ccEnabledSomewhere then derived(sanitizeArg(tm(tp)))
-      else EmptyAnnotation // strip retains-like annotations unless capture checking is enabled
+          EmptyAnnotation
 
     override def refersToParamOf(tl: TermLambda)(using Context): Boolean =
       refersToLambdaParam(tp, tl)
@@ -203,25 +197,13 @@ object Annotations {
     override def eql(that: Annotation) = that match
       case that: CompactAnnotation => this.tp `eql` that.tp
       case _ => false
-  end CompactAnnotation
 
-  /** Sanitize @retains arguments to approximate illegal types that could cause a compilation
-   *  time blowup before they are dropped ot detected. This means mapping all all skolems
-   *  (?n: T) to (?n: Any), and mapping all recursive captures that are not on CapSet to `^`.
-   *  Skolems and capturing types on types other than CapSet are not allowed in a
-   *  @retains annotation anyway, so the underlying type does not matter as long as it is also
-   *  illegal. See i24556.scala and i24556a.scala.
-   */
-  private def sanitize(tp: Type)(using Context): Type = tp match
-    case SkolemType(_) =>
-      SkolemType(defn.AnyType)
-    case tp @ AnnotatedType(parent, ann)
-    if ann.symbol.isRetainsLike && parent.typeSymbol != defn.Caps_CapSet =>
-      tp.derivedAnnotatedType(parent, ann.derivedClassAnnotation(defn.RetainsCapAnnot))
-    case tp @ OrType(tp1, tp2) =>
-      tp.derivedOrType(sanitize(tp1), sanitize(tp2))
-    case _ =>
-      tp
+  object CompactAnnotation:
+    def apply(tree: Tree)(using Context): CompactAnnotation =
+      val argTypes = tpd.allArguments(tree).map(_.tpe)
+      apply(annotClass(tree).typeRef.appliedTo(argTypes))
+
+  end CompactAnnotation
 
   private def isLambdaParam(t: Type, tl: TermLambda): Boolean = t match
     case TermParamRef(tl1, _) => tl eq tl1
@@ -311,9 +293,12 @@ object Annotations {
 
   object Annotation {
 
-    def apply(tree: Tree): Annotation = tree match
-      case tree: TypeTree => CompactAnnotation(tree.tpe)
-      case _ => ConcreteAnnotation(tree)
+    def apply(tree: Tree)(using Context): Annotation = tree match
+      case tree: TypeTree =>
+        CompactAnnotation(tree.tpe)
+      case _ =>
+        if annotClass(tree).isRetainsLike then CompactAnnotation(tree)
+        else ConcreteAnnotation(tree)
 
     def apply(cls: ClassSymbol, span: Span)(using Context): Annotation =
       apply(cls, Nil, span)
@@ -328,7 +313,9 @@ object Annotations {
       apply(atp, arg :: Nil, span)
 
     def apply(atp: Type, args: List[Tree], span: Span)(using Context): Annotation =
-      apply(New(atp, args).withSpan(span))
+      if atp.typeSymbol.isRetainsLike && args.isEmpty
+      then CompactAnnotation(atp)
+      else apply(New(atp, args).withSpan(span))
 
     /** Create an annotation where the tree is computed lazily. */
     def deferred(sym: Symbol)(treeFn: Context ?=> Tree): Annotation =
@@ -370,7 +357,7 @@ object Annotations {
    *  to indicate that the resulting typemap should drop the annotation
    *  (in derivedAnnotatedType).
    */
-  @sharable val EmptyAnnotation = Annotation(EmptyTree)
+  @sharable val EmptyAnnotation = ConcreteAnnotation(EmptyTree)
 
   def ThrowsAnnotation(cls: ClassSymbol)(using Context): Annotation = {
     val tref = cls.typeRef

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

@@ -4227,8 +4227,10 @@ object Types extends TypeUtils {
               val parent1 = mapOver(parent)
               if ann.symbol.isRetainsLike then
                 range(
-                  AnnotatedType(parent1, CaptureSet.empty.toRegularAnnotation(ann.symbol)),
-                  AnnotatedType(parent1, CaptureSet.universal.toRegularAnnotation(ann.symbol)))
+                  AnnotatedType(parent1,
+                    CompactAnnotation(defn.RetainsAnnot.typeRef.appliedTo(defn.NothingType))),
+                  AnnotatedType(parent1,
+                    CompactAnnotation(defn.RetainsCapAnnot.appliedRef)))
               else
                 parent1
             case _ => mapOver(tp)

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

@@ -201,8 +201,10 @@ class PostTyper extends MacroTransform with InfoTransformer { thisPhase =>
       inJavaAnnot = annot.symbol.is(JavaDefined)
       if (inJavaAnnot) checkValidJavaAnnotation(annot)
       try
-        val annotCtx = if annot.hasAttachment(untpd.RetainsAnnot)
-          then ctx.addMode(Mode.InCaptureSet) else ctx
+        val annotCtx =
+          if annot.hasAttachment(untpd.RetainsAnnot)
+          then ctx.addMode(Mode.InCaptureSet)
+          else ctx
         transform(annot)(using annotCtx)
       finally inJavaAnnot = saved
     }

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

@@ -11,7 +11,6 @@ import NameOps.*
 import collection.mutable
 import reporting.*
 import Checking.{checkNoPrivateLeaks, checkNoWildcard}
-import cc.CaptureSet
 import util.Property
 import transform.Splicer
 
@@ -570,10 +569,14 @@ trait TypeAssigner {
   def assignType(tree: untpd.Export)(using Context): Export =
     tree.withType(defn.UnitType)
 
-  def assignType(tree: untpd.Annotated, arg: Tree, annot: Tree)(using Context): Annotated = {
+  def assignType(tree: untpd.Annotated, arg: Tree, annotTree: Tree)(using Context): Annotated =
     assert(tree.isType) // annotating a term is done via a Typed node, can't use Annotate directly
-    tree.withType(AnnotatedType(arg.tpe, Annotation(annot)))
-  }
+    if annotClass(annotTree).exists then
+      tree.withType(AnnotatedType(arg.tpe, Annotation(annotTree)))
+    else
+      // this can happen if cyclic reference errors occurred when typing the annotation
+      tree.withType(
+        errorType(em"Malformed annotation $tree, will be ignored", annotTree.srcPos))
 
   def assignType(tree: untpd.PackageDef, pid: Tree)(using Context): PackageDef =
     tree.withType(pid.symbol.termRef)

tests/neg-custom-args/captures/lazyvals.check

@@ -16,7 +16,7 @@
    |                              Note that capability console is not included in capture set {x}.
    |
    | longer explanation available when compiling with `-explain`
--- Error: tests/neg-custom-args/captures/lazyvals.scala:16:18 ----------------------------------------------------------
+-- Error: tests/neg-custom-args/captures/lazyvals.scala:16:12 ----------------------------------------------------------
 16 |  val fun3: () ->{x} String = () => x() // error // error
-   |                  ^
-   |                  (x : () -> String) cannot be tracked since its capture set is empty
+   |            ^^^^^^^^^^^^^^^
+   |            (x : () -> String) cannot be tracked since its capture set is empty

tests/neg-custom-args/captures/spread-problem.check

@@ -7,6 +7,8 @@
 11 |  race(src1, src2) // error
    |       ^^^^^^^^^^
    |       Found:    (Source[T]^, Source[T]^)
-   |       Required: Seq[Source[T]^]
+   |       Required: Seq[Source[T]^{C}]
+   |
+   |       where:    C is a type variable with constraint >: scala.caps.CapSet and <: scala.caps.CapSet^
    |
    | longer explanation available when compiling with `-explain`