Overload selection differs for mapped types vs interfaces

[OliverJAsh]

TypeScript Version: 2.9.1

Search Terms: overload mapped types interface

Code

interface LoDashStatic {
  mapValues<T, TResult>(
      obj: { [index: string]: T },
      callback: (t: T) => TResult,
  ): { [index: string]: TResult };
  mapValues<T extends object, TResult>(
      obj: T,
      callback: (t: T[keyof T]) => TResult,
  ): { [P in keyof T]: TResult };
}

declare const _: LoDashStatic;

interface AbcObjectInterface {
  a: number;
  b: string;
  c: boolean;
}
type AbcObjectRecord = Record<"a" | "b" | "c", string>;

declare const abcObjectRecord: AbcObjectRecord;
declare const abcObjectInterface: AbcObjectInterface;

// Expected return type to be `{ a: number; b: number; c: string }` and got :-)
// The second overload is used, as expected.
_.mapValues(abcObjectInterface, (v) => 1);

// Expected return type to be `Record<"a" | "b" | "c", number>` but got `{ [index: string]: number }` :-(
// The first overload is used, unexpectedly.
_.mapValues(abcObjectRecord, (v) => 1);

Related Issues: DefinitelyTyped/DefinitelyTyped#26983 (comment)

[mhegazy]

Duplicate of #15300

[OliverJAsh]

Ta!