A field is promotable if it is private and final, and there is no
non-final field or concrete getter with the same name in the same
library. This is the rule the language team has chosen to adopt for
which fields are promotable, because it's sufficient to ensure that
the promotion is sound, and straightforward to specify. A more
complex rule could principle identify more fields that are soundly
promotable.
The rule has a hidden complexity, though: in circumstances where a
concrete class overrides noSuchMethod and implements an interface, if
the interface contains a private getter (or field) and the concrete
class doesn't provide an implementation for it, the compiler will
create a synthetic noSuchMethod forwarder; for soundness, this needs
to block promotion as well.
So the analyzer needs to partially replicate the logic the compiler
uses to determine whether a noSuchMethod forwarder is needed. This is
handled by a new file, field_promotability.dart, which walks the class
hierarchy to determine which private fields and getters are in the
interface of any given class but not in its implementation.
Field promotion is not yet enabled by default; to use it you need to
enable the experiment "inference-update-2".
Bug: https://github.com/dart-lang/language/issues/2020
Change-Id: I5f4ebb6b19626961b9b4c904d69670212668552b
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/262865
Reviewed-by: Samuel Rawlins <srawlins@google.com>
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>
Konstantin Shcheglov
56dcbe8c8e