Several unusual constructs that lead to unreachable code are now
recognized by flow analysis:
- Control flow after an expression of the form `e ?? other` or `e ??=
other`, where `e` has static type `Null` and `other` has static type
`Never`, is considered unreachable.
- Control flow predicated on an expression of the form `e is Never`
evaluating to `true` is considered unreachable.
- Control flow predicated on an expression of the form `e is! Never`
evaluating to `false` is considered unreachable.
- Control flow on the RHS of a null-aware access such as
`e?.property...`, `e?.property = ...` or `e?.method(...)`, where `e`
has static type `Null`, is considered unreachable (Note: this can
arise in the presence of extension methods).
Previously, these behaviors only took effect if `e` was a reference to
a local variable.
Note: the change to `regress/issue_31180` is because I’ve corrected
the behavior of implicit temporary variables to not undergo a type
change from `Null` to `dynamic`, so the dead code part of `null?[1]`
is now erroneous. (I had to make this change in order for the last
bullet above to work properly; without it, the type change to
`dynamic` prevents flow analysis from recognizing that the code to the
right of `?.` is unreachable.) There's no behavioral change to
correct code, but I've captured the behavioral change to incorrect
code in
`tests/language_2/null_aware/null_aware_index_on_null_error_test.dart`.
Bug: https://github.com/dart-lang/sdk/issues/49635
Change-Id: I8b24b3b040a34f897c0b61dcb9bd105be6d0af6d
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/251280
Commit-Queue: Paul Berry <paulberry@google.com>
Reviewed-by: Bob Nystrom <rnystrom@google.com>
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
This currently fails for the CFE with:
static error failures:
- Unexpected error at line 137, column 14: A value of type 'int?' can't be assigned to a variable of type 'int' because 'int?' is nullable and 'int' isn't.
- Unexpected error at line 137, column 25: Operand of null-aware operation '!' has type 'int' which excludes null.
Bug: https://github.com/dart-lang/sdk/issues/47338
Change-Id: Ia55e19a0bf296a8427f6510d6ddda5016acdecea
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/215101
Reviewed-by: Johnni Winther <johnniwinther@google.com>
Commit-Queue: Jake Macdonald <jakemac@google.com>
This changes the span reported from the _receiver_ to
the _use_ (method name, property name, operator token).
I think this change is overall an improvement.
Specifically, its a great improvement for cmdline
output, where the receiver and the "use" are on
different lines.
One possibly weird change is that if the operator is `[]`,
then I only highlight the `[` character. I don't know if
there is a better place, and I think this is fine.
Fixes https://github.com/dart-lang/sdk/issues/43708
Change-Id: Ie66ddf04b4904a367575193106385dd63ee39985
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/188680
Commit-Queue: Samuel Rawlins <srawlins@google.com>
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Paul Berry