This change updates the flow analysis support for field promotion
(which is not yet switched on by default) so that it supports field
accesses inside cascade expressions. The key moving parts are:
- The type hierarchy `PropertyTarget` (which is used by the client to
tell flow analysis whether the target of a property access is
`this`, `super`, or an ordinary expression) now has a new class,
`CascadePropertyTarget`, to represent the situation where the target
of the property access is an implicit reference to the target of the
innermost enclosing cascade expression.
- Flow analysis has two new methods on its API:
`cascadeExpression_afterTarget` and `cascadeExpression_end`, so that
the client can inform flow analysis when a cascade expression is
being analyzed.
- Flow analysis uses its `_makeTemporaryReference` method to track the
implicit temporary variable that stores the target of cascade
expressions. (This method was developed as part of flow analysis
support for patterns, where it creates the data structures necessary
to track the implicit variables that are created as part of pattern
desugaring).
- The "mini-AST" pseudo-language used by flow analysis unit tests now
has a way to represent cascade expressions and method invocations.
- In addition to unit tests for `_fe_analyzer_shared`, `analyzer`, and
`front_end`, there are new language tests in
`tests/language/inference_update_2` to test cascaded field
promotions in end-to-end fashion.
Bug: https://github.com/dart-lang/language/issues/2020
Change-Id: I21353bbc884ed599cb1739cecfb68ad1d975d18b
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/309220
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Reviewed-by: Johnni Winther <johnniwinther@google.com>
Commit-Queue: Paul Berry <paulberry@google.com>
