Logger onLevelChanged notification

[desistefanova]

Notify when the log level is changed.
Logger onLevelChanged broadcasts a stream of level values.
Fixes dart-lang/core#479

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[natebosch]

@jakemac53 - any concerns about this API?

[desistefanova]

Thank you for the good suggestions! I pushed the code review changes.

[jakemac53]

Looks like the pubspec version also needs to be updated to match the changelog 👍

[jakemac53]

We can publish soon, once this rolls internally and we confirm there are no issues (which I can't imagine there would be, but we have a policy to do that).

[jakemac53]

This is published now as version 1.2.0 @desistefanova

[kevmoo]

Beware adding things to types that are implemented! dart-lang/build#3514

[jakemac53]

This type really isn't intended to be implemented... obviously it was but I am not sure what this package could do about that. We don't want to change our versioning strategy I don't think just because of one breakage (this is still overall much less pain than doing breaking changes every time we add something).

Really, build_runner_core should have had a tight constraint on this package if it was going to implement this class, so that is my bad.

[natebosch]

This type really isn't intended to be implemented

Is it worth enforcing that? We could bump versions and add base.

[jakemac53]

Is it worth enforcing that? We could bump versions and add base.

We would need to see if we can migrate off implementing it in build_runner_core first

[natebosch]

I'm sure w can move to extends. I think we'd only have difficulty if we try to make the class final

[jakemac53]

Yeah good point, sgtm

[natebosch]

Ah, I was wrong 😞 , Logger also doesn't expose a generative constructor, so it doesn't make a difference if we use base or final...

[jakemac53]

Ah yeah that is probably why we implemented it