`path.getTypeAnnotation()` throws

[kangax]

Ran into this while fixing some Babili issues.

https://astexplorer.net/#/GbUDVxRZlD

Input Code

var a;
if (typeof a === "") {
  a;
}

Expected Behavior

Should not throw

Current Behavior

Throws "Invalid typeof value"

This is coming from inferAnnotationFromBinaryExpression which somehow produces null, passing it to createTypeAnnotationBasedOnTypeof in flow.js which doesn't understand "null" as one of the types.

/cc'ing @jeffmo since this is possibly related to Flow.

[babel-bot]

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[hzoo]

Oh thought it might of had to do with https://github.com/babel/babel/pull/3414 by @amasad but maybe not.

[jeffmo]

Hmm, AFAIK this isn't related to Flow other than syntax...but I'm not really familiar with this code.

Random guess: Does Babel try to infer types somewhere? If so, maybe it gets confused by the "" typeof comparison?

[kangax]

Yep, AFAICS, Babel tries to infer annotation — https://github.com/babel/babel/blob/master/packages/babel-traverse/src/path/index.js#L38

This suite looks useful and explains things a little — https://github.com/babel/babel/blob/8c35b320d37a957b629e75f59a9f52292cfd6b8e/packages/babel-traverse/test/inference.js#L57-L175

Looks like this is just an inference bug. I'll fix it.