The way this is accomplished is that in
`_FlowAnalysisImpl.nullAwareAccess_rightBegin`, any expression
reference associated with the target of the null-aware access is
restored, and the corresponding SSA node is associated with the guard
variable (if any). These changes ensure that if the null-aware access
is a property get, the subsequent call to `propertyGet` will pick up
the appropriate SSA node, so it will be able to locate the promotion
key for the property.
This functionality is only enabled when the language feature
`sound-flow-analysis` is enabled.
To prevent test regressions, a few related changes need to be made at
the same time:
- `_FlowAnalysisImpl.nullAwareAccess_end` is changed so that it clears
any expression info or expression reference that was associated with
the null-aware access expression. This prevents flow analysis
information from being erroneously propagated out of a null-aware
expression, which would have led to assertion failures when
analyzing null-aware expressions inside of conditional
expressions. This wasn't previously a problem because the expression
reference used to be consumed by
`_FlowAnalysisImpl.nullAwareAccess_rightBegin`, preventing further
expression references and expression infos from being recorded
further along in the null-aware access.
- The test framework in `mini_ast.dart` is fixed so that `!` is
considered to participate in null shorting. This was a bug in the
test framework that wasn't previously caught because it happened not
to produce any test failures.
- The analyzer's method `PostfixExpressionResolver._resolveNullCheck`
is changed so that it calls `nonNullAssert_end` before terminating
null-aware access. Previously, the order was swapped, causing
`nullAwareAccess_end` to be called before `nonNullAssert_end` when
analyzing expressions like `a?.b!`. This used to be benign, but now
that non-cascaded field accesses participate in field promotion,
flow analysis needs the methods to be called in the correct order.
Fixes https://github.com/dart-lang/language/issues/4344.
Bug: https://github.com/dart-lang/language/issues/4344
Change-Id: I523be1b4be1af3f68654a745187a546728c878fe
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/427820
Commit-Queue: Paul Berry <paulberry@google.com>
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Paul Berry
7436b97ba4