Fix regression in StyleSheet.setStyleAttributePreprocessor

[brentvatne]

This regression was caused by 199c918 - property values are initialized to true rather than a string that matches the property name now.

Test Plan:

• Expo depends on StyleSheet.setStyleAttributePreprocessor in order to map fontFamily names to internal unique ids that represent the font families in our asset system: https://github.com/expo/expo/blob/0c238c1b66e649ed8c90993164e850459f310b95/packages/expo/src/launch/registerRootComponent.tsx#L24
• It's easy to test this with an identity function: StyleSheet.setStyleAttributePreprocessor('fontFamily', name => name); - this will result in the following error:

fontFamily is not a valid style attribute
- node_modules/react-native/Libraries/StyleSheet/StyleSheet.js:347:23 in setStyleAttributePreprocessor

With this patch, this error is resolved.

Changelog:

• [General] [Fixed] - Update StyleSheet.setStyleAttributePreprocessor for new format of ReactNativeStyleAttributes.

[janicduplessis]

👍

@facebook-github-bot shipit

[facebook-github-bot]

@janicduplessis is landing this pull request. If you are a Facebook employee, you can view this diff on Phabricator.

[elicwhite]

Yikes. setStyleAttributePreprocessor is sketchy. Thanks for catching this. Should definitely be handing it being true. The attributes it is checking is what React uses to know how to process host element's props and thus we want those objects to be as small as possible which is why they use true.

[react-native-bot]

@brentvatne merged commit 0408533 into facebook:master.

[brentvatne]

Yikes. setStyleAttributePreprocessor is sketchy

it is a bit, but we do this kind of processing internally so I think there needs to be some way to expose the same power to users. I actually originally added this code iirc but definitely open to ideas for other ways to solve the use case mentioned in op