Paul Berry
97edad1568
Whenever a pattern performs an implicit `is` test, flow analysis attempts to determine whether the `is` test is guaranteed to succeed; if it is, then flow analysis considers the code path in which the `is` test fails to be unreachable. This allows flow analysis to recognize switch statements that are trivially exhaustive (because one of the cases is guaranteed to match), avoiding spurious errors such as "variable must be assigned before use" or "missing return statement". This change upgrades the logic for computing when an `is` test is guaranteed to succeed, so that it accounts for type erasure of extension types. This brings flow analysis's treatment of switch statements into closer alignment with the exhaustiveness checker, which should reduce the risk of confusing error messages. For more information see https://github.com/dart-lang/language/issues/3534#issuecomment-1885839268. Fixes https://github.com/dart-lang/language/issues/3534. Bug: https://github.com/dart-lang/language/issues/3534 Change-Id: Ib73d191e04e7fa8c0e6888c2733dae73d8f389da Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/345822 Reviewed-by: Chloe Stefantsova <cstefantsova@google.com> Commit-Queue: Paul Berry <paulberry@google.com>