This enables the front end to skip the old-style (enum-based)
exhaustiveness checking algorithm when pattern support is enabled,
because with pattern support enabled, switches on enums are required
to be exhaustive (this will be checked by the new exhaustiveness
checking algorithm).
That in turn means that in the future, when we remove support for
language versions that lack patterns support, we will be able to
remove the old-style exhaustiveness checking algorithm.
This change has a small effect on code generated by the WASM back-end
(the only back-end that uses `isExplicitlyExhaustive`): for a switch
statement that is exhaustive *and* has an unreachable `default`
clause, after testing all the cases, the WASM back-end will generate a
branch to the `default` case. Previously it would instead generate an
`unreachable` instruction. There should be no behavioural difference
because the instruction in question is unreachable in both cases.
Also, there should be negligible code size difference because the body
of the `default` case is being emitted either way.
Bug: https://github.com/dart-lang/sdk/issues/50419
Change-Id: Id6bd7d9a540cb1b4d9c3624db8ff494438276bea
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/274924
Reviewed-by: Aske Simon Christensen <askesc@google.com>
Commit-Queue: Paul Berry <paulberry@google.com>
Reviewed-by: Johnni Winther <johnniwinther@google.com>
Paul Berry
9b294b846b