Array of tuple literal not assignable to iterable of tuple with --lib es2015 -t es5

TypeScript Versions: 3.5.1, 3.5.3 (currently typescript@latest), 3.6.0-beta (currently typescript@beta), 3.6.0-dev.20190808 (currently typescript@next)

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Code

// Works:
declare function foo<T>(i: Iterable<T>): T
const x = foo([1]); // infers a: number

// Fails:
declare function bar<T, U>(j: Iterable<[T, U]>): [T, U]
const y = bar([[1, 'a']]);
//             ^^^^^^^^
//             Argument of type '(string | number)[][]' is not assignable to
//             parameter of type 'Iterable<[string | number, string | number]>'.

// workaround:
declare function qux<T, U>(j: Array<[T, U]> | Iterable<[T, U]>): [T, U]
const z = qux([[1, 'a']]); // infers z: [number, string]

Expected behavior: variable y is inferred to be of type [number, string] and parameter j is inferred to be of type Array<[number, string]>

Actual behavior: error TS2345: Argument of type '(string | number)[][]' is not assignable to parameter of type 'Iterable<[string | number, string | number]>'.

Playground Link

Related Issues: maybe #29311 ?

[dragomirtitian]

Cloned repo, ran tsc .\hello.ts -target es2015, no error.

Are you sure you don’t have another tsc installed on your system? Run a tsc- -v

[RyanCavanaugh]

@rbuckton can you explain what’s happening? Bug?