Optional properties that are not set on nested objects cause errors

[massimonewsuk]

interface Row {
    status: string | null;
    name: string;
}

interface Data {
    nested: {
        status?: string;
        name: string;
    };
}

function mapData(row: Row): Data {
    const entity: Data = {
        nested: {
            name: row.name,
        }
    };
    if (row.status !== null) {
        entity.nested.status = row.status;
    }
    return entity;
}

Reproducible on the flow try thingy... Just copy and paste the code above.

This works fine in TypeScript.

[apsavin]

It seems that it's possible to avoid this error if you avoid interfaces: try

[ghost]

Alternatively, you could create a type for nested.

Try Flow

[massimonewsuk]

@idiostruct In this case the nested doesn't really make sense to have a type

@apsavin Thanks for letting me know I can use types, that workaround works for me. However, it still looks like this is a bug.

[TrySound]

The problem can be reproduced simpler
https://flow.org/try/#0PQKgBAAgZgNg9gdzCYAoVBLAdgFwKYBOUAhgMZ5gAixOxYA3qmGFngM74AmAXA082A40ArmwD8vDgWwBzANz8AvgsXpScLBzCcaxXtVpgAvH2asOeHqbABIITlG8A5FNlOlqZUA

[massimonewsuk]

@TrySound thanks for the smaller piece of code... the original codebase I was having this in was several thousand lines and took me almost 20 minutes to get it down to my original example... I'm glad you could distil it further 😄

[ajs139]

I believe this is the same problem with nested properties:
https://flow.org/try/#0C4TwDgpgBAYg9nKBeKBvAUFKBLAJgLigGdgAnbAOwHMAaKdAX3XVEigCEBDU5NTHAsTKUqUAD5QKAVwA2MmowDczAMZwKJKADME+eIhQYseQgHJcWi6YUNl6ABQ64hLqQCUioA

[massimonewsuk]

Still an issue in v0.67.0

[massimonewsuk]

Still an issue in v0.70.0