When determining whether a switch statement is exhaustive, it's
important for the exhaustiveness algorithm to ignore cases containing
`when` clauses, since a `when` clause creates the possiblity that the
case won't match.
Previously, the way this was done in the analyzer was for the
`SpaceCreator.createRootSpace` method to create an unknown space for
cases containing `when` clauses. This approach produced the correct
behavior when determining whether the switch statement as a whole was
exhaustive, but since it discarded information about the pattern being
matched, it limited the ability to determine whether an individual
case was reachable, leading to
https://github.com/dart-lang/sdk/issues/56710.
To fix this, `SpaceCreator.createRootSpace` is changed so that it
always produces a space that describes the case pattern, regardless of
whether a `when` clause is present, and instead,
`computeExhaustiveness` is responsible for ensuring that the case is
properly excluded from the determination of whether the switch is
exhaustive. This allows `computeExhaustiveness` to properly computate
whether each individual case is reachable, even for cases that have
`when` clauses.
This change in approach produced some minor differences in the test
cases in `pkg/_fe_analyzer_shared/test/exhaustiveness/data`, but these
differences are not user-observable.
Fixes https://github.com/dart-lang/sdk/issues/56710.
Change-Id: I36629a77c4c1832fb1b8abb6ea7b109e0ca14373
Bug: https://github.com/dart-lang/sdk/issues/56710
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/384326
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Reviewed-by: Johnni Winther <johnniwinther@google.com>
Commit-Queue: Paul Berry <paulberry@google.com>
Paul Berry
a3c696fa58