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.

Reproduce the diagnostic in the linked TypeScript Playground using versions 4.2.3, 4.3.5, and 5.7.2, then compare it with the no-spread variant. Trace the checker path that reports the indexed-access mismatch and add a regression test; done means the final diagnostic preserves the payload comparison instead of referring to EventPayloads as a whole.