[analyzer_plugin] `FooMixin` classes are not mixins

[FMorschel]

I was looking at the analyzer_plugin API, and I see that AssistContributorMixin and DartAssistsMixin, for example, are not mixins but the docs say we should only use them as mixins and not extend or implement them.

But we can't mixin them because we get the class_used_as_mixin diagnostic. Since they don't have the mixin modifier. I'm not sure what we should do here, @srawlins.

[TejasSojitra12]

Patch your own mixin: Create a proper mixin that wraps or delegates to the original class:

mixin MyAssistContributorMixin on AssistContributorMixin {}

Then use with MyAssistContributorMixin. This satisfies the compiler.

[FMorschel]

Sure, that would work. But it doesn't make the public API of the package correct. This is what I'm opening this issue for. We can surely do workarounds like this. Thanks for the tip though, someone might need it!

[bwilkerson]

@srawlins

[srawlins]

I'm not sure either. I'd have to look into how they're used. We might remove them, or make them mixins, or change the documentation.

[bwilkerson]

@srawlins Are these classes being used in the new plugin support? I'm just wondering whether this is worth addressing. Especially given that converting them to mixins is a breaking change.

[srawlins]

Ah, we can probably remove these when we deprecate legacy plugins. They are not used otherwise:

$ git grep AssistContributorMixin
pkg/analyzer_plugin/api.txt:  AssistContributorMixin (class extends Object implements AssistContributor):
pkg/analyzer_plugin/api.txt:    new (constructor: AssistContributorMixin Function())
pkg/analyzer_plugin/doc/tutorial/assists.md:The class `AssistContributorMixin` defines a support method that makes it easier
pkg/analyzer_plugin/doc/tutorial/assists.md:the class `AssistContributorMixin`, then implement the method `computeAssists`.
pkg/analyzer_plugin/doc/tutorial/assists.md:    with AssistContributorMixin
pkg/analyzer_plugin/lib/utilities/assist/assist_contributor_mixin.dart:abstract class AssistContributorMixin implements AssistContributor {

[FMorschel]

Yeah, I found those in the tutorial. Also see #61732, about the tutorial being outdated.

[bwilkerson]

@FMorschel Can this issue be closed, given that analyzer_plugin will be deprecated when the new plugin support ships?

[FMorschel]

Yes, it can.