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Abstract empty values should fail RequireObjectCoercible #2515
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NTillmann
reviewed
Aug 31, 2018
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The empty value is supposed to be unreachable, so it does not really matter if it is modeled as undefined in this situation. I do plan to get rid of this use of the empty value in the near future, which will make this into a non issue. Meanwhile, I think this change is fine. |
hermanventer
approved these changes
Aug 31, 2018
trueadm
approved these changes
Aug 31, 2018
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This fixes a bug it took me a while to track down. Unfortunately creating a repro was really difficult. I was observing the following invariant in
Referencebeing triggered.https://github.com/facebook/prepack/blob/fddfc6f0c52fa8f49fb0cb1208f34cefcb95dca3/src/environment.js#L1425-L1431
Digging in, the bad base was a deep conditional
AbstractValuewhere all the leaf nodes wereEmptyValueand__bottomValue. (Constructed from a number oftry/catch/throws.) ThisAbstractValueshould have simplified to justEmptyValuethenRequireObjectCoercible()should have thrown a runtimeTypeErrorafter seeing theEmptyValue. This is what I observed in local tests when trying to reproduce this issue.After looking at the error in the large React Native bundle I’m working in I discovered that the simplifier was throwing an error since the simplification count was exceeded. This is fine and normal. The issue was that
RequireObjectCoercible()does not handle complex emptyAbstractValues well. If failing simplification is a normal part of Prepack operation we should make sure methods likeRequireObjectCoercible()can handle complexAbstractValues as well as simple ones.This PR does that.