Migration tool sometimes suggests `.whereOrNull` where it shouldn't

[stereotype441]

Consider the following code:

f<U>(Iterable<U> it) => it.where((s) => s != null);

The migration tool changes this to:

import 'package:collection/collection.dart' show IterableNullableExtension;

f<U>(Iterable<U> it) => it.whereNotNull();

However, this doesn't work because the signature of whereNotNull is:

extension IterableNullableExtension<T extends Object> on Iterable<T?> {
  Iterable<T> whereNotNull() => ...;
}

When the type system tries to solve for a substitution T=... that makes the extension apply, it gets T=U, but that doesn't work because U is not a subtype of Object.

So the migration tool shouldn't change the where to whereNotNull in this case.

[stereotype441]

As of 1c7fe71, the null safety migration tool has been removed from active development and retired. No further work on the tool is planned.

If you still need help, or you believe this issue has been closed in error, please feel free to reopen.