Incorrect error attribution on indexed access, when using object spread operator

🔎 Search Terms

spread operator destructuring error, spread error message, object indexed access error message

🕗 Version & Regression Information

• This changed between versions 4.2.3 and 4.3.5

⏯ Playground Link

Playground link, 5.7.2

💻 Code

type EventPayloads = {
    completeSprint: {
        automationId: string,
        spaceId: string,
    },
    sendMessage: {
        message: string,
    },
}

type CompletedEvent<T extends keyof EventPayloads> = {
    [E in T]: {
        type: E,
        payload: EventPayloads[E],
        appName: string,
    }
}[T]

function overwriteAppName<T extends keyof EventPayloads>(
    scheduled: CompletedEvent<T>,
): CompletedEvent<T> {
    const { appName, ...rest } = scheduled
    // Weird error message here, starting in 4.3
    return {
        ...rest,
        appName: "test",
    }
}

🙁 Actual behavior

The return statement has the following error:

Type 'Omit<CompletedEvent<T>, "appName"> & { appName: string; }' is not assignable to type 'CompletedEvent<T>'.
  Types of property 'payload' are incompatible.
    Type 'CompletedEvent<T>["payload"]' is not assignable to type 'EventPayloads[T]'.
      Type '{ type: T; payload: EventPayloads[T]; appName: string; }' is missing the following properties from type 'EventPayloads': completeSprint, sendMessage(2322)

The first three lines make sense, but the last line is bizarre enough that I suspect it's a bug in either the reporting/checking logic.

Given that EventPayloads and CompletedEvent are completely different objects, this error made me think I had missed an indexing step somewhere, but after rereading the code multiple times I'm pretty sure I didn't (it seems like a type error in the type error).

Also, my best possible explanation for the reduction in this step

    Type 'CompletedEvent<T>["payload"]' is not assignable to type 'EventPayloads[T]'.
      Type '{ type: T; payload: EventPayloads[T]; appName: string; }' is missing the following properties from type 'EventPayloads': completeSprint, sendMessage(2322)

is that the algorithm eliminated the indexed access on both sides, so that

but this is clearly incorrect considering T != "payload".

🙂 Expected behavior

Given the penultimate line of the error, I would expect the final line to compare payload types, i.e. { automationId: string, spaceId: string } vs. { message: string }

Type 'Omit<CompletedEvent<T>, "appName"> & { appName: string; }' is not assignable to type 'CompletedEvent<T>'.
  Types of property 'payload' are incompatible.
    Type 'CompletedEvent<T>["payload"]' is not assignable to type 'EventPayloads[T]'.
      Type '{ type: T; payload: EventPayloads[T]; appName: string; }' is missing the following properties from type 'EventPayloads': completeSprint, sendMessage
        Type 'CompletedEvent<T>["payload"]' is not assignable to type '{ automationId: string; spaceId: string; } & { message: string; }'.
          Type 'EventPayloads[T]' is not assignable to type '{ automationId: string; spaceId: string; } & { message: string; }'.
            Type '{ automationId: string; spaceId: string; } | { message: string; }' is not assignable to type '{ automationId: string; spaceId: string; } & { message: string; }'.
              Type '{ automationId: string; spaceId: string; }' is not assignable to type '{ automationId: string; spaceId: string; } & { message: string; }'.
                Property 'message' is missing in type '{ automationId: string; spaceId: string; }' but required in type '{ message: string; }'.
                  Type 'EventPayloads[T]' is not assignable to type '{ automationId: string; spaceId: string; }'.
                    Type 'CompletedEvent<T>["payload"]' is not assignable to type '{ automationId: string; spaceId: string; }'.
                      Type 'EventPayloads[T]' is not assignable to type '{ automationId: string; spaceId: string; }'.
                        Type '{ automationId: string; spaceId: string; } | { message: string; }' is not assignable to type '{ automationId: string; spaceId: string; }'.
                          Type '{ message: string; }' is missing the following properties from type '{ automationId: string; spaceId: string; }': automationId, spaceId(2322)

Additional information about the issue

I've tagged the issue with object spread operator because removing the spreads resolves the error. But I don't actually know whether the bug is intrinsic to spreads.

Reproduziere die Diagnose im verlinkten TypeScript Playground mit den Versionen 4.2.3, 4.3.5 und 5.7.2 und vergleiche sie anschließend mit der Variante ohne Spread. Verfolge den Checker-Pfad, der den Indexed-Access-Mismatch meldet, und füge einen Regressionstest hinzu; abgeschlossen ist die Aufgabe, wenn die endgültige Diagnose den Payload-Vergleich beibehält, statt sich auf EventPayloads als Ganzes zu beziehen.