UnmodifiableMapMixin and others aren't Dart3-ready

[oprypin]

UnmodifiableMapMixin should become a mixin or mixin class. Otherwise it is not ready for use with Dart 3 / prefer_mixin.
All usages of it are expected to be within a with clause.

Others that I noticed are NonGrowableListMixin, UnmodifiableSetMixin

[lrhn]

https://dart-review.googlesource.com/c/sdk/+/288240 should hopefully land soon-ish.

[oprypin]

Is that related? This is about 'package:collection'

[lrhn]

(Already updated the URL, pasted the wrong one originally.)

[oprypin]

🙂 I think it's still different - 'dart:collection' vs 'package:collection'

[lrhn]

Argh. My bad. Wrong issue tracker entirely. (Naming footgun!)

Yes, yes they should.

[oprypin]

Ping on this issue. I think this is high priority to resolve and make a release of this library ahead of Dart 3.

Also cc @mit-mit @devoncarew

[lrhn]

There is technically no reason to eagerly change anything, since pre-3.0 code classes can still be used as mixins without the mixin modifier. As long as this package's min-SDK is 2.18.0, mixin in should keep workin.

It's only an issue if someone tries to interpret the pre-3.0 code as post-3.0 code, ignoring the languge-version of the pubspec, which is not a safe thing to do since 3.0 is a breaking change for the language.
(And I believe the case where that was happening is no longer an issue, so we're not in any rush to release a 3.0 version.)

It's another issue that migrating the package to 3.0 properly should, rightfully, mean a major version increment.
Those are harder to release.