This fixes an assertion getting triggered in dart2wasm when compiling
ACX gallery. The bad state is an InstanceInvocation where the receiver
is a type with no instantiable subtypes. Dart2wasm expects TFA to tree
shake such unreachable calls.
The issue arises when an awaited expression includes a call where the
receiver is promoted to an uninstantiable type. Dart2wasm does a modular
transform to hoist the awaited expression to its own statement:
https://github.com/dart-lang/sdk/blob/main/pkg/dart2wasm/lib/await_transformer.dart#L12
This hoisting takes the expression out of the promotion context and TFA
is then unable to mark the call as unreachable (given the unpromoted
type *is* instantiable).
The CFE includes the promoted type on the VariableGet which gets copied
over in the hoist transform. So a solution here is to narrow the
inferred type with the promoted static type when available.
An alternative solution here is to hoist *after* TFA. But that doesn't
protect other transforms that could trigger this same issue.
Change-Id: I903bdde53f57a007568cd47a20cbac986c42d18d
Tested: Test cases added
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/456900
Reviewed-by: Alexander Markov <alexmarkov@google.com>
Reviewed-by: Martin Kustermann <kustermann@google.com>
Nate Biggs
885c6e22dd