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Reject capture sets in context bounds #26724

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Reject capture sets in context bounds #26724

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50c749b
Reject capture sets in context bounds
natsukagami Aug 6, 2026
3c88cc8
Add test
natsukagami Aug 6, 2026
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11 changes: 8 additions & 3 deletions compiler/src/dotty/tools/dotc/typer/Typer.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -48,7 +48,7 @@ import staging.StagingLevel
import reporting.*
import Nullables.*
import NullOpsDecorator.*
import cc.{Setup, CheckCaptures, isRetainsLike, derivesFromCapSet}
import cc.{Setup, CheckCaptures, isRetainsLike, derivesFromCapSet, RetainingAnnotation}
import config.MigrationVersion
import dotty.tools.dotc.core.Mode.Interactive
import transform.CheckUnused.withOriginalName
Expand Down Expand Up @@ -2690,8 +2690,13 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
val tycon = typedType(tree.tycon)
def spliced(tree: Tree) = untpd.TypedSplice(tree)
val tparam = untpd.Ident(tree.paramName).withSpan(tree.span.withEnd(tree.span.point))
if Feature.ccEnabled && typed(tparam).tpe.derivesFromCapSet then
report.error(em"Capture variable `${tree.paramName}` cannot have a context bound.", tycon.srcPos)
if Feature.ccEnabled then
if typed(tparam).tpe.derivesFromCapSet then
report.error(em"Capture variable `${tree.paramName}` cannot have a context bound.", tycon.srcPos)
tycon.tpe match
case AnnotatedType(_, _ : RetainingAnnotation) =>
report.error(em"Context bound `${tree.tycon}` cannot have a capture set.", tycon.srcPos)
case _ =>
if tycon.tpe.typeParams.nonEmpty then
val tycon0 = tycon.withType(tycon.tpe.etaCollapse)
typed(untpd.AppliedTypeTree(spliced(tycon0), tparam :: Nil))
Expand Down
11 changes: 11 additions & 0 deletions tests/neg-custom-args/captures/in-context-bounds.scala
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Original file line number Diff line number Diff line change
@@ -0,0 +1,11 @@
package e

import caps.*

trait A[T]
trait B[T] extends caps.SharedCapability

def wantsA1[C^, T: (A^{C})](x: T): A[T] = summon[A[T]] // error
def wantsA2[T: (A^)](x: T): A[T] = summon[A[T]] // error
def wantsA3[T: B](x: T): B[T] = summon[B[T]] // ok

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