Typescript, FormDataConsumer, getSource is possibly undefinded

[PavelTankovich]

What you were expecting:
I expect the getSource function from FormDataConsumer not to be undefined

What happened instead:
When I try to use getSource from FormDataConsumer I get a problem related to ts.
TS2722: Cannot invoke an object which is possibly 'undefined'.
Because of this I have to add an extra condition in the code.

Steps to reproduce:
Use getSource from FormDataConsumer in an application with ts

Related code:

<FormDataConsumer>
  {({ scopedFormData, getSource, ...rest }) => scopedFormData.id !== 'BadId' && <MyInputs source={getSource('inputsList')} />}
</FormDataConsumer>;

Other information:

Environment

• React-admin version: ^4.9.0
• React version: ^18.2.0
• Browser: all
• Typescript: ^5.0.2

[slax57]

getSource is only provided if <FormDataConsumer> is used inside a <SimpleFormIterator>, that's why it's typed as getSource?: (source: string) => string;

Besides, we don't have any TS warning in the simple demo (https://stackblitz.com/github/marmelab/react-admin/tree/master/examples/simple?file=src%2Fposts%2FPostEdit.tsx%3AL168)

So I'm not sure why you encountered that error.
Can you provide a reproduction?

[PavelTankovich]

@slax57 Sure, here's an example, please take a look, https://codesandbox.io/p/sandbox/gifted-hooks-162e3r?file=%2Fsrc%2FExample%2Findex.tsx%3A18%2C68-18%2C77
You can see ts error

[slax57]

@PavelTankovich Thanks for the repro.

I've played around a bit with it, and it turns out, this is dependent on the TS config in place.

I haven't figured out which config property yet, but as soon as you add a tsconfig.json file, even with the bare minimum content like

{
  "compilerOptions": {
    "rootDir": "src",
    "jsx": "react",
    "allowSyntheticDefaultImports": true
  },
  "exclude": ["**/*.spec.ts", "**/*.spec.tsx", "**/*.spec.js"],
  "include": ["src"]
}

then the error disappears and the IDE considers the type to be (source: string) => string. I'm not sure why.

Anyway, I don't see how we could improve the type for now, so the best we could do is mention this gotcha in the documentation.

Hence I'll label this as a documentation issue.