When casting a getter return value that requires a covariance check, the
CFE inserts an AsExpression where both the operand type and
tested-against type are statically identical (the instantiated member
return type, e.g. Callable<void Function(num)>).
The types.dart optimizer previously assumed that because the static
types matched, the runtime type arguments must also match, and optimized
away the type-argument checks. However, in a covariance check, the
dynamic value returned is a supertype (e.g. Callable<void
Function(int)>) due to class parameter covariance.
This change safely rewrites the static operand type of a covariance check
by preserving the InterfaceType structure but using calculateBounds to
rewrite its type arguments to their upper bounds (falling back to Object?
or Object for non-interface types). This allows us to keep class-check
optimizations active while remaining sound.
TEST=tests/language/covariant/callable_class_field_getter_test.dart
Fixes https://github.com/dart-lang/sdk/issues/53091
Change-Id: Ia64ea90b1bad2f7c1dab81cc3385103507b97b3e
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/508425
Reviewed-by: Martin Kustermann <kustermann@google.com>
Auto-Submit: Kevin Moore <kevmoo@google.com>
Commit-Queue: Kevin Moore <kevmoo@google.com>
Kevin Moore
23a289417d