Prior to this change, the first phase of flow analysis, in which flow
analysis "looks ahead" to see which variables are potentially assigned
in each code block, was failing to properly account for variables that
are assigned by pattern assignment expressions. This "look ahead"
information is used by flow analysis to determine the effects of
nonlinear control flow (e.g. to figure out which variables to demote
at the top of a loop, or to figure out which variables are potentially
assigned inside a closure). As a result, it was possible to construct
correct code that would be rejected by the analyzer and compiler, as
well as incorrect code that would (unsoundly) be accepted.
The fix is to call `AssignedVariables.write` from the analyzer's
`FlowAnalysisVisitor`, and from the CFE's `BodyBuilder`, to let flow
analysis know about variable assignments that occur inside pattern
assignment expressions.
Fixes#52745.
Change-Id: I0e6f426a5c5c36f214d5a206aaf5a2de0bfdaac1
Bug: https://github.com/dart-lang/sdk/issues/52745
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/310502
Auto-Submit: Paul Berry <paulberry@google.com>
Reviewed-by: Johnni Winther <johnniwinther@google.com>
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>
Paul Berry
2ca7380ab0