commit 98f585d092f3fe9306c7b913ae8aa914d2ac20c7
author Paul Berry <paulberry@google.com> Fri Feb 10 15:24:08 2023 +0000
committer Commit Queue <dart-scoped@luci-project-accounts.iam.gserviceaccount.com> Fri Feb 10 15:24:08 2023 +0000
tree 7b6499d0d4f5ef4a70a8f1d6d153c09eeba85d74
parent 0bdaafe39593f7b55849515973f1e3bace3c01d7

Flow analysis: fix improper handling of scrutinee EqualityInfo.

Previously, we stored an EqualityInfo object representing the
scrutinee at the time of entry to the top level of the pattern; then
when handling, for example, a relational pattern using `==`, we used
that EqualityInfo object to decide how to handle the equality check,
*even if we were no longer at the top level of the pattern*.  As a
result, we would sometimes come to incorrect conclusions about
relational patterns inside subpatterns.  For example, we would fail to
see that `if ((null,) case (== null,))` is a guaranteed match, because
when processing the `== null` pattern, we would erroneously use the
EqualityInfo for `(null,)` (which is *not* `null`).

To solve this, we only store the scrutinee *reference* at the top
level of the pattern (this is sufficient to allow us to decide whether
or not to promote the scrutinee).  When we encounter a pattern like
`== null`, we compute the appropriate EqualityInfo directly based on
the ExpressionInfo, type, and reference that are appropriate to the
current pattern level.

Bug: https://github.com/dart-lang/sdk/issues/50419
Change-Id: I4d1bc34fcb2d238e7b69e1b88df50b389410963c
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/282162
Reviewed-by: Johnni Winther <johnniwinther@google.com>
Commit-Queue: Paul Berry <paulberry@google.com>