Not clear if @visibleForTesting elements should be visible in other packages

[sigurdm]

https://api.flutter.dev/flutter/meta/visibleForTesting-constant.html says

Tools, such as the analyzer, can provide feedback if

• ...
• the declaration is referenced outside of its defining library or a library which is in the test folder of the defining package.

But the analyzer doesn't warn if an element is used in a test from another package.

It is not clear if the documentation or the analyzer is wrong here. I think both interpretations are useful in some cases.

Maybe we even need two different annotations

[bwilkerson]

In this case I think the documentation is correct and that the analyzer is wrong. I don't know how big of a breaking change it would be to fix it.

It's an interesting question as to whether there is enough need to have a visibleForTestingAnywhere annotation that allows the current behavior. (Or a visibleForTestingInSamePackage annotation if we want to avoid a breaking change.) I suspect that it's rare for a package author to want to allow dependencies in other packages on non-public API, so I think in those cases it's better for authors of dependent packages to clearly mark that the use of the API is known to be prohibited and that they're risking having their code broken by changes to the defining package.

[sigurdm]

I suspect that it's rare for a package author to want to allow dependencies in other packages on non-public API

I think it make sense to have API that is "public, but for testing only" perhaps it uses reflection, or mocks setup in a way that is not suitable for deployment time, but useful for testing.

[sigurdm]

In the discussions around dart-lang/dartdoc#4048 several people commented (some in an internal chat thread) that they had or intended to use @visibleForTesting for exactly that purpose.