[Compiler Bug]: TypeError: Cannot read properties of undefined (reading 'length')

[kireerik]

What kind of issue is this?

• React Compiler core (the JS output is incorrect, or your app works incorrectly after optimization)
• babel-plugin-react-compiler (build issue installing or using the Babel plugin)
• eslint-plugin-react-compiler (build issue installing or using the eslint plugin)
• react-compiler-healthcheck (build issue installing or using the healthcheck script)

Link to repro

https://playground.react.dev/#N4Igzg9grgTgxgUxALhHCA7MAXABAYQgFsAHTBDPAXlwApgSYISEZsBPAXwEpcqA+ADoZcuADwATAJYA3XI2asOVYLV4D5TFm3YA6ADYUA5tgAWnAPT8QnIA

Repro steps

1. render the component

We do not call the property function named property, but the error occurs regardless (when the component is rendered).

other versions:
babel-plugin-react-compiler: experimental
react-compiler-runtime-polyfill: 0.x

How often does this bug happen?

Every time

What version of React are you using?

18.x

[josephsavona]

@kireerik Thanks for filing this! The compiler currently assumes that the code is using a type system such as TypeScript or Flow, which both require checks to access possibly nullable data. For example, TypeScript and Flow would error on the example if property was nullable, and require using something like property?.length or using an if (property != null) { ... } guard.

But we know that not everyone is using a type system, so we're also looking at options for inferring more conservative dependencies if a type system isn't being used. We've implemented this behind a feature flag, but we don't want to have to make users mess with complex configurations, so we're iterating on how to choose the right default automatically.