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Drop reach capabilities #26246

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42690ec
Change or disable reach capability tests
odersky Jun 6, 2026
c4c816d
Drop deprecated features of caps
odersky Jun 6, 2026
1d75476
Don't produce reach captures
odersky Jun 7, 2026
22534ac
Disable parsing reach capabilities
odersky Jun 8, 2026
f861212
Drop internal reach capability definitions
odersky Jun 8, 2026
fd576ca
Update syntax.md
odersky Jun 8, 2026
af2a1e7
Drop `@use` annotation handling
odersky Jun 8, 2026
8354768
Simplify isUseParam logic
odersky Jun 8, 2026
11c5b92
Drop remaining references to `use`.
odersky Jun 8, 2026
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3 changes: 0 additions & 3 deletions compiler/src/dotty/tools/dotc/ast/untpd.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -573,9 +573,6 @@ object untpd extends Trees.Instance[Untyped] with UntypedTreeInfo {
case _ =>
false

def makeReachAnnot()(using Context): Tree =
New(scalaAnnotationInternalDot(tpnme.reachCapability), Nil :: Nil)

def makeReadOnlyAnnot()(using Context): Tree =
New(scalaAnnotationInternalDot(tpnme.readOnlyCapability), Nil :: Nil)

Expand Down
100 changes: 25 additions & 75 deletions compiler/src/dotty/tools/dotc/cc/Capability.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -39,8 +39,7 @@ import collection.immutable
* | +-- SetCapability -----+-- TypeRef
* | +-- TypeParamRef
* |
* +-- DerivedCapability -+-- Reach
* +-- Only
* +-- DerivedCapability -+-- Only
* +-- ReadOnly
* +-- Maybe
*
Expand Down Expand Up @@ -106,41 +105,23 @@ object Capabilities:

/** The readonly capability `x.rd`. We have {x.rd} <: {x}.
*
* Read-only capabilities cannot wrap maybe capabilities
* but they can wrap reach capabilities. We have
* (x?).readOnly = (x.rd)?
* Read-only capabilities cannot wrap maybe capabilities.
*/
case class ReadOnly(underlying: CoreCapability | RootCapability | Reach | Restricted)
case class ReadOnly(underlying: CoreCapability | RootCapability | Restricted)
extends DerivedCapability:
def newLikeThis(c: Capability) = ReadOnly(c.asInstanceOf)

/** The restricted capability `x.only[C]`. We have {x.only[C]} <: {x}.
*
* Restricted capabilities cannot wrap maybe capabilities or read-only capabilities
* but they can wrap reach capabilities. We have
* Restricted capabilities cannot wrap maybe capabilities or read-only capabilities.
* We have
* (x?).restrict[T] = (x.restrict[T])?
* (x.rd).restrict[T] = (x.restrict[T]).rd
*/
case class Restricted(underlying: CoreCapability | RootCapability | Reach, cls: ClassSymbol)
case class Restricted(underlying: CoreCapability | RootCapability, cls: ClassSymbol)
extends DerivedCapability:
def newLikeThis(c: Capability) = Restricted(c.asInstanceOf, cls)

/** If `x` is a capability, its reach capability `x*`. `x*` stands for all
* capabilities reachable through `x`.
* We have `{x} <: {x*} <: dcs(x)}` where the deep capture set `dcs(x)` of `x`
* is the union of all capture sets that appear in covariant position in the
* type of `x`. If `x` and `y` are different variables then `{x*}` and `{y*}`
* are unrelated.
*
* Reach capabilities cannot wrap read-only capabilities or maybe capabilities.
* We have
* (x?).reach = (x.reach)?
* (x.rd).reach = (x.reach).rd
* (x.only[T]).reach = (x*).only[T]
*/
case class Reach(underlying: ObjectCapability) extends DerivedCapability:
def newLikeThis(c: Capability) = Reach(c.asInstanceOf)

/** A class for the global root capabilities referenced as `caps.any` and `caps.fresh`.
* They do not subsume other capabilities, except in arguments of `withCapAsRoot` calls.
*/
Expand All @@ -149,7 +130,6 @@ object Capabilities:
override val maybe = Maybe(this)
override val readOnly = ReadOnly(this)
override def restrict(cls: ClassSymbol)(using Context) = Restricted(this, cls)
override def reach = unsupported("caps.any.reach")
override def singletonCaptureSet(using Context) = CaptureSet.universal
override def captureSetOfInfo(using Context) = singletonCaptureSet
override def cached[C <: DerivedCapability](newRef: C): C = unsupported("cached")
Expand Down Expand Up @@ -334,7 +314,7 @@ object Capabilities:
end ResultCap

/** A trait for references in CaptureSets. These can be NamedTypes, ThisTypes or ParamRefs,
* as well as three kinds of AnnotatedTypes representing readOnly, reach, and maybe capabilities.
* as well as three kinds of AnnotatedTypes representing readOnly, only, and maybe capabilities.
* If there are several annotations they come with an order:
* `*` first, `.only` next, `.rd` next, `?` last.
*/
Expand Down Expand Up @@ -371,7 +351,7 @@ object Capabilities:
def readOnly: ReadOnly | Maybe = this match
case Maybe(ref1) => Maybe(ref1.readOnly)
case self: ReadOnly => self
case self: (CoreCapability | RootCapability | Reach | Restricted) => cached(ReadOnly(self))
case self: (CoreCapability | RootCapability | Restricted) => cached(ReadOnly(self))

def restrict(cls: ClassSymbol)(using Context): Restricted | ReadOnly | Maybe = this match
case Maybe(ref1) => Maybe(ref1.restrict(cls))
Expand All @@ -380,14 +360,7 @@ object Capabilities:
val combinedCls = leastClassifier(prevCls, cls)
if combinedCls == prevCls then self
else cached(Restricted(ref1, combinedCls))
case self: (CoreCapability | RootCapability | Reach) => cached(Restricted(self, cls))

def reach: Reach | Restricted | ReadOnly | Maybe = this match
case Maybe(ref1) => Maybe(ref1.reach)
case ReadOnly(ref1) => ReadOnly(ref1.reach.asInstanceOf[Reach | Restricted])
case Restricted(ref1, cls) => Restricted(ref1.reach.asInstanceOf[Reach], cls)
case self: Reach => self
case self: ObjectCapability => cached(Reach(self))
case self: (CoreCapability | RootCapability) => cached(Restricted(self, cls))

/** Is this a maybe reference of the form `x?`? */
final def isMaybe(using Context): Boolean = this ne stripMaybe
Expand All @@ -411,11 +384,6 @@ object Capabilities:
case self: ResultCap => self.origin.classifier
case _ => NoSymbol

/** Is this a reach reference of the form `x*` or a readOnly or maybe variant
* of a reach reference?
*/
final def isReach(using Context): Boolean = this ne stripReach

final def stripMaybe(using Context): Capability = this match
case Maybe(ref1) => ref1
case _ => this
Expand All @@ -435,13 +403,6 @@ object Capabilities:
final def stripRestricted(using Context): Capability =
stripRestricted(defn.NothingClass)

final def stripReach(using Context): Capability = this match
case Reach(ref1) => ref1
case ReadOnly(ref1) => ref1.stripReach.readOnly
case Restricted(ref1, cls) => ref1.stripReach.restrict(cls)
case Maybe(ref1) => ref1.stripReach.maybe
case _ => this

/** Is this reference a root capability or a derived version of one?
* These capabilities have themselves as their captureSetOfInfo.
*/
Expand Down Expand Up @@ -594,7 +555,6 @@ object Capabilities:

/** Tests whether the capability derives from capability class `cls`. */
def derivesFromCapTrait(cls: ClassSymbol)(using Context): Boolean = this match
case Reach(ref1) => ref1.widen.derivesFromCapTraitDeeply(cls)
case self: DerivedCapability => self.underlying.derivesFromCapTrait(cls)
case self: CoreCapability => self.superType.derivesFromCapTrait(cls)
case _ => false
Expand Down Expand Up @@ -660,8 +620,6 @@ object Capabilities:
ref1.transClassifiers
case Maybe(ref1) =>
ref1.transClassifiers
case Reach(_) =>
captureSetOfInfo.transClassifiers
case self: CoreCapability =>
if self.derivesFromCapability then toClassifiers(self.inheritedClassifier)
else captureSetOfInfo.transClassifiers
Expand All @@ -685,8 +643,6 @@ object Capabilities:
ref1.tryClassifyAs(cls)
case Maybe(ref1) =>
ref1.tryClassifyAs(cls)
case Reach(_) =>
captureSetOfInfo.tryClassifyAs(cls)
case self: CoreCapability =>
if self.derivesFromCapability then self.derivesFrom(cls)
else captureSetOfInfo.tryClassifyAs(cls)
Expand Down Expand Up @@ -784,7 +740,6 @@ object Capabilities:
this.subsumes(y.cls.sourceModule.termRef)
case _ => false
|| this.match
case Reach(x1) => x1.subsumes(y.stripReach)
case Restricted(x1, cls) => y.isKnownClassifiedAs(cls) && x1.subsumes(y)
case x: TermRef => viaInfo(x.info)(subsumingRefs(_, y))
case x: TypeRef if assumedContainsOf(x).contains(y) => true
Expand Down Expand Up @@ -886,10 +841,6 @@ object Capabilities:
|| y.match
case y @ TermRef(ypre: Capability, _) =>
recur(x, ypre)
case Reach(y1) =>
x match
case Reach(x1) => recur(x1, y1)
case _ => false
case Maybe(y1) =>
x match
case Maybe(x1) => recur(x1, y1)
Expand Down Expand Up @@ -947,7 +898,6 @@ object Capabilities:
c match
case _: ReadOnly => ReadOnlyCapability(c1)
case Restricted(_, cls) => OnlyCapability(c1, cls)
case _: Reach => ReachCapability(c1)
case _: Maybe => MaybeCapability(c1)
case _ => c1

Expand Down Expand Up @@ -1117,9 +1067,9 @@ object Capabilities:
case _ =>
mapFollowingAliases(t)

override def mapCapability(c: Capability, deep: Boolean): Capability = c match
override def mapCapability(c: Capability): Capability = c match
case GlobalAny => LocalCap(origin)
case _ => super.mapCapability(c, deep)
case _ => super.mapCapability(c)

override def fuse(next: BiTypeMap)(using Context) = next match
case next: Inverse => assert(false); Some(IdentityTypeMap)
Expand All @@ -1132,9 +1082,9 @@ object Capabilities:
case t @ CapturingType(_, refs) => mapOver(t)
case _ => mapFollowingAliases(t)

override def mapCapability(c: Capability, deep: Boolean): Capability = c match
override def mapCapability(c: Capability): Capability = c match
case _: LocalCap => GlobalAny
case _ => super.mapCapability(c, deep)
case _ => super.mapCapability(c)

def inverse = thisMap
override def toString = thisMap.toString + ".inverse"
Expand Down Expand Up @@ -1181,7 +1131,7 @@ object Capabilities:
if t.binder == this.binder then paramSyms(t.paramNum).termRef else t
case _ => mapOver(t)

override def mapCapability(c: Capability, deep: Boolean): Capability = c match
override def mapCapability(c: Capability): Capability = c match
case r: ResultCap if r.binder == this.binder =>
resultToAny.get(r) match
case Some(f) => f
Expand All @@ -1191,7 +1141,7 @@ object Capabilities:
anyToResult(f) = r
f
case _ =>
super.mapCapability(c, deep)
super.mapCapability(c)

class Inverse extends BiTypeMap:
def apply(t: Type): Type =
Expand All @@ -1201,7 +1151,7 @@ object Capabilities:
binder.paramRefs(paramSyms.indexOf(t.symbol))
case _ => mapOver(t)

override def mapCapability(c: Capability, deep: Boolean): Capability = c match
override def mapCapability(c: Capability): Capability = c match
case f: LocalCap if f.owner == sym =>
anyToResult.get(f) match
case Some(r) => r
Expand All @@ -1210,7 +1160,7 @@ object Capabilities:
resultToAny(r) = f
anyToResult(f) = r
r
case _ => super.mapCapability(c, deep)
case _ => super.mapCapability(c)

def inverse = thisMap
override def toString = thisMap.toString + ".inverse"
Expand Down Expand Up @@ -1239,7 +1189,7 @@ object Capabilities:
case _ =>
mapOver(t)

override def mapCapability(c: Capability, deep: Boolean) = c match
override def mapCapability(c: Capability) = c match
case c @ ResultCap(binder) =>
if localBinders.contains(binder) then c // keep bound references
else
Expand All @@ -1249,7 +1199,7 @@ object Capabilities:
lc.hiddenSet.markSolved(provisional = false)
lc
seen.getOrElseUpdate(c, localCapSkolem) // map free references to LocalCap
case _ => super.mapCapability(c, deep)
case _ => super.mapCapability(c)
end subst

subst(tp)
Expand All @@ -1268,7 +1218,7 @@ object Capabilities:

def apply(t: Type) = mapOver(t)

override def mapCapability(c: Capability, deep: Boolean) = c match
override def mapCapability(c: Capability) = c match
case c: LocalCap =>
if variance >= 0 then
if sym.exists && !c.ccOwner.isContainedIn(sym) then
Expand All @@ -1282,15 +1232,15 @@ object Capabilities:
case GlobalFresh =>
ResultCap(mt) // if variance <= 0 we leave the fresh to be flagged later
case _ =>
super.mapCapability(c, deep)
super.mapCapability(c)

//.showing(i"mapcap $t = $result")
override def toString = "toVar"

object inverse extends BiTypeMap:
def apply(t: Type) = mapOver(t)

override def mapCapability(c: Capability, deep: Boolean) = c match
override def mapCapability(c: Capability) = c match
case c @ ResultCap(`mt`) =>
val primary = c.primaryResultCap
primary.origin match
Expand All @@ -1301,7 +1251,7 @@ object Capabilities:
case origin: LocalCap =>
origin
case _ =>
super.mapCapability(c, deep)
super.mapCapability(c)

def inverse = ToResult.this
override def toString = "toVar.inverse"
Expand All @@ -1313,12 +1263,12 @@ object Capabilities:
*/
class RetractResult(rcs: SimpleIdentitySet[ResultCap])(using Context) extends TypeMap:
def apply(t: Type) = mapOver(t)
override def mapCapability(c: Capability, deep: Boolean) = c match
override def mapCapability(c: Capability) = c match
case c: ResultCap if rcs.exists(_.primaryResultCap == c.primaryResultCap) =>
c.primaryResultCap.origin match
case origin: LocalCap => origin
case _ => c
case _ => super.mapCapability(c, deep)
case _ => super.mapCapability(c)

/** Replace all occurrences of `caps.any` or LocalCap in parts of this type by an existentially bound
* variable bound by `mt`. Stop at function or method types since these have been mapped before.
Expand Down
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