Intersection with AbstractComponent leads to misleading errors

[omninonsense]

Flow version: 0.104

Expected behavior

Don't error when the intersection can be rendered as a React component.

Alternatively, if this is another strange design decision regarding React.AbstractComponent, can we at least error early (as soon as we try to intersect with AbstractComponent) instead of in a random place in the code.

Actual behavior

Flow complains that React.Component is not a React component when it appears in an intersection with AbstractComponent.

This is a kind of dumbed down example: https://flow.org/try/#0PTAEAEDMBsHsHcBQiCWBbADrATgF1AFSgCGAzqAEoCmxAxvpNrGqAOTY32vIigAqACxTlhoAK6kqAE1BVok+AKodQKAHahcSzQE8M6gOalEtaGXIBJNbmVYzuYgCNoVAMLMsaqtYA8ABQA+WQAPGzUpcmo6XAASd0xYL19A0ABvRFBQUlwdFyl4z29cCykALizcbEMAbkQAX2QcjCpQAGUcvILEov8mDFIAGlArbOI1WioggF5KTliAQUds7GiupNxe2H6hkYdxydAAMmHrW1h7Jxc1nrGdAOQpKlNiFUgxcdwURNA0YgBrKibbYnUb7AIACgAlOV2rlpNdkn1BiC9hMArUTIlsqACqAZr8AT5UnUhqwpCgAG6sCGQ5C0LH4RzEfIwjrwjzdXzE0mkDBjal40A+XHAAJAA

However, a real-world example of this can be found in flow-typed's typedefs for styled-components: https://github.com/flow-typed/flow-typed/pull/3517/files#diff-2b77bbf95ac6caa4414db8ad19a62162 (search for should render as the correct element for the whole test that reproduces this, and for noExpectError for the immediate line below it that triggers the error).

More information about it can be found in flow-typed/flow-typed#3517 (comment) (and some subsequent comments).

/cc @goodmind

[goodmind]

/cc @jbrown215

[jbrown215]

Alternatively, if this is another strange design decision regarding React.AbstractComponent

If it's by design, I stopped caring, because the Flow devs are stubborn af.

If you're going to be snarky and rude, at least be correct.

The way you're referring to InterpolatableComponent in StyledComponent is referring to an instance of the class. An instance of InterpolatableComponent is not a React component-- the class is. I agree that the error message leaves much to be desired.

Here, I fixed it for you.

Alternatively, if this is another strange design decision regarding React.AbstractComponent

If you're referring to the fact that we don't carry defaultProps around, you should consider more kinds of React components. AbstractComponent is meant to model all of them, and not all of them have defaultProps. Moreover, defaultProps are being deprecated on function components. Maybe what you interpret as a "strange design decision" is actually a decision made that considered more information than you did.

[goodmind]

I still can't get this to work

[goodmind]

This probably isn't related tho

[goodmind]

It works only if I specify generic explicitly, but no inference

[omninonsense]

Alternatively, if this is another strange design decision regarding React.AbstractComponent

If you're referring to the fact that we don't carry defaultProps around, you should consider more kinds of React components. AbstractComponent is meant to model all of them, and not all of them have defaultProps. Moreover, defaultProps are being deprecated on function components. Maybe what you interpret as a "strange design decision" is actually a decision made that considered more information than you did.

As far as I can tell, the feature is not deprecated yet, it is going to be deprecated. As it currently stands, Flow removed a feature at the type level that still exists, and is used in a lot of existing libraries, application code and tools.

The fact we're using a tweet as a reference point feels ridiculous. The only other official source I can find is a MR that adds a disabled warning, this being mention in a few issues. I—for the life of me—can not find this properly documented anywhere. Documentation in Flow for this present-incompatible, futuristic behaviour should be the bare minimum.

Anyway, I don't want to go off-topic more than we already did. If you think it's a good idea, I can open a PR (or an issue) about documenting this.

If you're going to be snarky and rude, at least be correct.

I am slightly frustrated with the way Flow team generally communicates (and the documentation in certain places). The frustration was slightly elevated when I wrote that comment. None of this is really a justification for my behaviour; I realise the rudeness doesn't help, I regret being rude. I apologise to you and everyone else on the Flow team.

Rudeness is uncalled for regardless of whether I was right or wrong technically.

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The way you're referring to InterpolatableComponent in StyledComponent is referring to an instance of the class. An instance of InterpolatableComponent is not a React component-- the class is. I agree that the error message leaves much to be desired.

Here, I fixed it for you.

Thank you! 😄

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Once again, I really am genuinely sorry for being rude, and upsetting/offending you, or anyone else. Thank you for all the work you're doing! ❤️