We produce a diagnostic under the following conditions:
- For compound assignments, if the type read from the LHS is nullable
(this is illegal after NNBD, and requires user intervention to fix).
- For compound assignments, if the type returned from the combiner is
not assignable to the LHS (this was required prior to NNBD, but it
is a stricter condition after migration, both because the LHS might
have a non-nullable type, and because implicit downcasts are not
allowed).
- For null-aware assignments, if the type read from the LHS is
non-nullable (this indicates that once strong mode is enabled, the
assignment will be dead code).
Bug: https://github.com/dart-lang/sdk/issues/38676
Change-Id: Icb242ba36437e38364ada069880831eb05e3a513
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/145664
Reviewed-by: Mike Fairhurst <mfairhurst@google.com>
Paul Berry
bf56b2ca2c