commit c430a3b4aa05843f7b9693d6078f63d0dbbf3023
author Paul Berry <paulberry@google.com> Tue Dec 13 14:36:57 2022 +0000
committer Commit Queue <dart-scoped@luci-project-accounts.iam.gserviceaccount.com> Tue Dec 13 14:36:57 2022 +0000
tree 16c713549eeef232ca96f66ed71e41277ebe144b
parent 9169abc8f4607b4e250b501cfac989dc052cb509

Patterns flow analysis: fix handling of empty exhaustive switch statements.

I previously thought that the only possible situation where a switch
statement over a valid type could be exhaustive without containing any
cases was if the scrutinee type was the empty record type (`()`).  But
that isn't true at all:

- The empty record type is inhabited by empty record objects, so such
  a switch statement would not be exhaustive after all.

- It is possible for the user to create a type that can be
  exhaustively switched over with zero cases: by creating an abstract
  sealed class without any subclasses.

In the latter case, I think it makes the most sense to treat the code
after the switch as unreachable, because that's the normal behaviour
of a switch over an exhaustive type with no `break`s.  It is sound to
do so because the type is uninhabited, therefore the body of the
switch statement itself will never be reached.

Bug: https://github.com/dart-lang/sdk/issues/50419
Change-Id: Ibc0a21226f25ae155db994343874354d5b8e4f7d
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/274621
Reviewed-by: Johnni Winther <johnniwinther@google.com>
Commit-Queue: Paul Berry <paulberry@google.com>