Typescript chooses wrong overload for RxJs's reduce call

[WiseBird]

TypeScript Version: typescript@2.8.0-dev.20180221

Search Terms:
rxjs reduce overload

Code

import {Observable} from 'rxjs';

(null as Observable<{attribute: string, values: string[]}>)
    .reduce((acc, val) => ({
        ...acc,
        [val.attribute]: val.values,
    }), {});

Go to definition leads to

export declare function reduce<T>(this: Observable<T>, accumulator: (acc: T, value: T, index: number) => T, seed?: T): Observable<T>;

Expected behavior:
No errors

Actual behavior:

Error:(12, 14) TS2339: Property 'attribute' does not exist on type '{}'.
Error:(12, 30) TS2339: Property 'values' does not exist on type '{}'.

Reproduction: https://github.com/WiseBird/ts_rxjs_reduce

More info
I also try letable operators with the same effect:

import {Observable} from 'rxjs/Rx';
import {reduce} from 'rxjs/operators';

(null as Observable<{attribute: string, values: string[]}>)
    .let(
        reduce((acc, val) => ({
            ...acc,
            [val.attribute]: val.values,
        }), {}),
    );

Apparently ts chooses wrong overload and uses seed's type for value's type.

With simplified typings ts works OK:

interface Observable<T> {
    reduce(accumulator: (acc: T[], value: T) => T[], seed: T[]): Observable<T[]>;
    reduce(accumulator: (acc: T, value: T) => T, seed?: T): Observable<T>;
    reduce<R>(accumulator: (acc: R, value: T) => R, seed: R): Observable<R>;
}

(null as Observable<{attribute: string, values: string[]}>)
    .reduce((acc, val) => ({
        ...acc,
        [val.attribute]: val.values,
    }), {});

Go to declaration leads to

reduce<R>(accumulator: (acc: R, value: T) => R, seed: R): Observable<R>;

[aluanhaddad]

Getting the types right for this method has been a pain. It's not really a typescript issue. You can read about it starting with this issue and then follow the thread of referenced tissues and PRS ReactiveX/rxjs#2338