Incorrect TS7022 error in loop

[mysticatea]

Bug Report

Tsc threw TS7022 error on the place that is not any type.

        const group = await fetchGroup(nextId); // (id: string) => Promise<Group>
        //    ^^^^^ 'group' implicitly has type 'any' because it does not have a type annotation and is referenced directly or indirectly in its own initializer. (7022)

🔎 Search Terms

• 7022

#33191 and #39183 are maybe related. But in this case, the return type of fetchGroup() does not depend on parameters; that always Promise<Group> explicitly. Also, the type of nextId is always string at the line.

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about 7022

(3.3.3 ... 4.2.0-dev.20210127)

⏯ Playground Link

Playground link with relevant code

💻 Code

interface Group {
    parentId: string | undefined
    //...
}

declare function fetchGroup(id: string): Promise<Group>

async function fetchAncestorGroups(leafId: string): Promise<Group[]> {
    const groups: Group[] = [];
    let nextId: string | undefined = leafId;

    while (nextId) {
        const group = await fetchGroup(nextId);
        //    ^^^^^ 'group' implicitly has type 'any' because it does not have a type annotation and is referenced directly or indirectly in its own initializer. (7022)
        groups.push(group);
        nextId = group.parentId;
    }
    return groups.reverse();
}

🙁 Actual behavior

'group' implicitly has type 'any' because it does not have a type annotation and is referenced directly or indirectly in its own initializer. (7022)

🙂 Expected behavior

No errors.

[RyanCavanaugh]

This really is a circularity; the fact that we can higher-order-reason our way out of it doesn't make it not a circularity. The core checking algorithm doesn't have mechanisms in place that would allow this to be resolved.

[disjukr]

#30308 also related

[JoostK]

This is no longer reported as an error since TS 5.0, unlike this scenario.