Fix #21868, #21869, and #21870: handle CapsOf in more places #21875
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| @@ -198,7 +198,7 @@ extension (tp: Type) | |||
| || tp.isRootCapability | |||
| ) && !tp.symbol.isOneOf(UnstableValueFlags) | |||
| case tp: TypeRef => | |||
| tp.symbol.isAbstractOrParamType && tp.derivesFrom(defn.Caps_CapSet) | |||
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@odersky Do you remember why we require the arguments of CapsOf to be abstract before? I think any type derived from CapSet should work.
noti0na1
changed the title
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Strange, we're consistently getting a CI failure |
bracevac
changed the title
If we do not strip the capture set at this point, then the type will be transformed twice and we'll get the same error message twice.
| def boom(): Unit^{C^} // error | ||
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| trait Abstract: | ||
| type C <: CapSet^ |
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Idealy, we'd like to retrict the capture parameter and member bounded by >: CapSet^{} <: CapSet^, which can forbid instantiating to meaningless types, like Nothing.
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That's certainly cleaner. The question is how far we want to take it for now. A fully general solution would also have to deal with the presence of explicit lower bounds, which could be themselves type variables, etc.
trait Abstract[L >: CapSet^{}]:
type T >: L <: CapSet^Maybe let's track this in a separate issue? The point of the current fix is to prevent the uncaught exception and compiler crash.
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I don't think this is an issue, as long as L is also bounded by CapSet.
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As the below examples show, there's a still a few quirks. I'm also somewhat uneasy with automatically presuming that the lower bound of a CapSet^-bounded type variable is CapSet^{}. E.g., should this always be the case, or only with cc enabled?
Since the specific issues are resolved, let's merge this and have a separate issue to make capture set intervals and subtyping airtight.
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At some point, we should probably make intersection and unions work as well: class Concrete2 extends Abstract:
type C = CapSet^{} & CapSet^{}
def boom() = () // error
class Concrete3 extends Abstract:
type C = CapSet^{} | CapSet^{}
def boom() = () // errorIt's not unreasonable to expect |
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OK, so this is weird: import language.experimental.captureChecking
import caps.*
trait Abstract[X >: Nothing]: // Concrete2 and 3 fail with this lower bound, but work with X >: CapSet^{}
type C >: X <: CapSet^
def boom(): Unit^{C^}
class Concrete extends Abstract[CapSet^{}]:
type C = CapSet^{}
def boom() = () // ok
class Concrete2 extends Abstract[CapSet^{}]:
type C = CapSet^{} & CapSet^{}
def boom() = () // error
class Concrete3 extends Abstract[CapSet^{}]:
type C = CapSet^{} | CapSet^{}
def boom() = () // errorWe get (now properly reported as an error) "Illegal capture reference ..." as long as |
bracevac
added
cc-experiment
Fix #21868, #21869, and #21870