Possible issue with Array.prototype.map or disjoint unions of array types

[NicholasBoll]

Array.prototype.map seems to fail if given a disjoint union of different array types

TypeScript Version: 2.2.2 (also tried 2.3.4. Reproducible on the Playground as well)

Code

function map<T>(items: T[] | string[]) {
    items.map(x => x)
}

Also fails:

function map<T>(items: Array<T> | Array<string>) {
    items.map(x => x)
}

Expected behavior:
Maybe this should work?

Actual behavior:
Type Error:

Cannot invoke an expression whose type lacks a call signature. Type '{ <U>(this: [string, string, string, string, string], callbackfn: (value: string, index: number, ...' has no compatible call signatures.

Workaround
The following does work:

function map<T extends object | string>(items: T[]) {
  items.map(x => x)
}

Perhaps not a bug since a workaround exists - I don't know if the workaround would be a preferred method?

[mhegazy]

Duplicate of #7294

[mhegazy]

Automatically closing this issue for housekeeping purposes. The issue labels indicate that it is unactionable at the moment or has already been addressed.