Can't append two string literal type values

[justinwoo]

I'd like to append two const string literal values together and extract or assign a new string literal type.

Sorry if this is a duplicate of something, I couldn't find an existing issue.

TypeScript Version: 2.4.2 / PlayGround

Code

const APPLE = 'APPLE';
const PINEAPPLE = 'PINEAPPLE'

type AppleLiteralType = 'APPLE'
const APPLE2: AppleLiteralType = APPLE

// this is only `string`,
// even though it's two literals appended
const APPLEPINEAPPLE = APPLE + PINEAPPLE;

// Type 'string' is not assignable to type '"APPLEPINEAPPLE"'.
const Test: 'APPLEPINEAPPLE' = APPLE + PINEAPPLE;
const Test2: 'APPLEPINEAPPLE' = `${APPLE}${PINEAPPLE}`;

Expected behavior:
Test and/or Test2 should work with the `'APPLEPINEAPPLE' string literal type

Actual behavior:
Test and Test2 both turn into string types

[ikatyang]

Duplicate of #12940 or #17512.

[justinwoo]

Ahh, thanks!