Explain unresolvable references better #20477
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odersky
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@jchyb I had to add another test to the BestEffortCompilation blacklist. Here the compiler survives a MissingType exception in Typer but continuing leads to the same exception being thrown without a handler that reports an error. |
smarter
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May 28, 2024
We run into problems when referring to a member of a self type of a class
that it not also a member of the class from outside via an asSeenFrom.
One example is in 11226.scala where we see:
```scala
trait ManagedActorClassification { this: ActorEventBus =>
def unsubscribe(subscriber: Subscriber): Unit
}
class Unsubscriber(bus: ManagedActorClassification) {
def test(a: ActorRef): Unit = bus.unsubscribe(a) // error
}
```
The problem is that `unsubscribe` refers to the type `Subscriber` which
is not resolvable as a member of `bus`. one idea could be to rule out
type signatures like `unsubscribe`, similar how we rule out public signatures
referring to private members. But this could rule out existing valid programs.
For instance, the `unsubscribe` signature is unproblematic if it gets only
called with prefixes that inherit `ActorEventBus`. You could say that the
problem was instead that the type of `bus` was not specific enough.
In the long term, maybe restructing the signature is the right move. But for
now, we just try to give better error messages in the case of existing failures.
Fixes scala#11226
Co-authored-by: Guillaume Martres <[email protected]>
WojciechMazur
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Jul 9, 2024
Backports #20477 to the LTS branch. PR submitted by the release tooling. [skip ci]
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We run into problems when referring to a member of a self type of a class that it not also a member of the class from outside via an asSeenFrom.
One example is in 11226.scala where we see:
The problem is that
unsubscriberefers to the typeSubscriberwhich is not resolvable as a member ofbus. one idea could be to rule out type signatures likeunsubscribe, similar how we rule out public signatures referring to private members. But this could rule out existing valid programs. For instance, theunsubscribesignature is unproblematic if it gets only called with prefixes that inheritActorEventBus. You could say that the problem was instead that the type ofbuswas not specific enough.In the long term, maybe restricting the signature is the right move. But for now, we just try to give better error messages in the case of existing failures.
Fixes #11226