Eli White
60e3921f9c
Summary: Pull Request resolved: https://github.com/facebook/react-native/pull/49340 This tool enables checking the boundary between JavaScript and Native for backwards incompatible changes to protect against crashes. This is useful for: - Local Development - Over the Air updates on platforms that support it - Theoretically: Server Components with React Native Check out the Readme for more information Changelog: [General][Added] Open Sourcing React Native's Compatibility Check Reviewed By: panagosg7 Differential Revision: D69476742 fbshipit-source-id: 8af6039839c5475c1258fa82d9750a9320cf0751
1.8 KiB
This tool is essentially a type checker, and as such it can be difficult to understand the data flow. Luckily, there are fairly extensive tests which can aid in ramping up.
This tool is made up of 3 primary stages: TypeDiffing, VersionDiffing, and ErrorFormatting.
At a high level, the schemas are passed to TypeDiffing which is the pure typechecker. It returns all differences between the types. VersionDiffing then interprets these results and decides if some of those changes are actually safe in the context of React Native’s JS/Native boundary.
For example, if you have a NativeModule method that returns a string union
small | medium | large. Any changes to that union would be flagged by
TypeDiffing as incompatible. However, adding a value to that union is safe
because it ensures your JS code handles more cases than native returns. Removing
a value from that union isn’t safe though because it means your JS no longer
handles something native might return which could cause an exception.
VersionDiffing encodes the logic of what is safe and what isn’t; property/union/enum additions and removals, changing something from optional to required and vice versa, etc. VersionDiffing has knowledge of components and modules.
VersionDiffing returns a set of incompatible changes, which then gets passed to ErrorFormatting. ErrorFormatting does as you’d expect, converting these deep objects into nicely formatted strings.
When contributing, some principles:
- Keep TypeDiffing and ErrorFormatting pure. They should only know about JavaScript types, not React Native specific concepts
- Add tests for every case you can think of. This codebase can be complex and hard to reason about when making changes. The only way to stay sane is to be able to rely on the tests to catch anything bad you’ve done. Do yourself and future contributors a favor.