[0.18.0-rc] class properties now needs a semicolon but packager throws a cryptic error

[gre]

class A { 
 foo = () => console.log("ooo")
}

this used to work, but now in 0.18.0-rc

TransformError: .../index.js: Cannot read property 'error' of null

Do we need to explicitely add some babel plugin now for this? or is it a bug?

---

answer is you must use a semicolon now, so:

class A { 
 foo = () => console.log("ooo");
}

---

But the error is not straightforward, this shouldn't break like this in packager

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[toadums]

I think you need a semicolon after the arrow function, babel changed this in 6.4.0

babylon: #3225 throw parse error if class properties do not have a semicolon.

From my looking around last night, there is no plugin that removes this check

[benjreinhart]

babel/babel#3225 Is breaking everyone's RN apps if they re-install node modules. I sort of agree with their reasoning for the breaking change but it is annoying that it is transparently upgraded if the react-native module is reinstalled without even upgrading RN itself.

[gre]

@benjreinhart what do you mean "if they re-install node modules" ? is there a cache somewhere? Because i've rm -rf node_modules multiple time already

[benjreinhart]

Yeah.. that's why you're getting the error. When you reinstall the react-native module it is upgrading a babel transform which contains the commit in that link I provided that throws those syntax errors.

So the fact that it is throwing errors isn't a bug. It was a bug that that code worked in the first place, at least according to the pull request I linked to above.

[corbt]

I can confirm this in 0.18-rc. I noticed the same error as @gre: TransformError: [some file]: Cannot read property 'error' of null but didn't know what caused it. After downgrading back to 0.17 I was confronted with the class properties error @benjreinhart mentions, although in 0.17 the babel error message was shown instead of the cryptic packager one, so I could fix it.

I don't have a problem with babel's behavior here (I don't care if I have to put semicolons after class properties) but the cryptic error that the transformer throws in 0.18-rc should be classified as a bug. It gives no help in solving the problem.

[gre]

@benjreinhart oh yeah I see.

Thanks @toadums for pointing the error cause, this is going to be a pain for everyone using this feature as the error message is totally not straightforward, but hopefully when people will search for this they might fall here.
I wish there were a migration tool – or at least a deprecated message logged when they break things like this.

[corbt]

@gre I would leave this open; packager should report the babel failure so that users can find and fix the class-properties bug in their code. This is the behavior in 0.17. I think this is a regression in packager.

[gre]

@corbt sorry I thought you meant it was a bug in babel, opened :)

[hzoo]

@gre There's no official migration tool but I made a PR for JSCS to add autofix for class properties for the requireSemicolons rule real quick for this. babel/babel#3225 (comment). I'l try to get a new version out later today, otherwise follow the steps I mention. Also we will add a deprecation message next time.

[satya164]

@gre @corbt Probably should open another issue about Packager not showing Babel errors.