utf8.encode should return Uint8List

[Hixie]

...for similar reasons as described in #31547, #27818, and #31784.

For now I'm just going to assume it returns a Uint8List and cast the return value, but that's dubious at best.

[lrhn]

That would be a reasonable change.
It's technically breaking since someone might implement Utf8Codec, but they really shouldn't.

[tvolkert]

The APIs make this difficult because to do this, you'd have to change Encoding to extend Codec<String, Uint8List>, which would in turn mean that you'd be forcing callers of utf8.decode() (and similar for ASCII, Latin1, etc) to pass in Uint8List. Conceptually, that seems like an equally logical change to make, but it's also not backwards compatible and much more likely to break callers.

It may still be worth it - it just requires more care.

[lrhn]

We can change Utf8Codec.encode and Utf8Encoder.convert to return Uint8List without changing the API for Encoding. A Uint8List is-a List<int> so it satisfies the Codec/Converter<String,List<int>> interface.

[tvolkert]

https://dart-review.googlesource.com/c/sdk/+/101742

[tvolkert]

Breaking change request: #36900

[tvolkert]

This is done now.