Mapping of a tuple with array functions causes an error. #17591

// A *self-contained* demonstration of the problem follows...
// Test this by running `tsc` on the command-line, rather than through another build tool such as Gulp, Webpack, etc.
//
// create a sample array of a tuple, of type (string, number)
//
const testArray: Array<[string, number]> = [['A',3], ['B', 7]];
//
// convert them to an array of a tuple, of type (string, string, number)
//
const mapToArray: Array<[string, string, number]> = testArray.map(([str, num]) => [str, str, num]);

//
// create a sample array of a tuple, of type (string, number)
//
const testArray: Array<[string, number]> = [['A',3], ['B', 7]];
//
// convert them to an array of a tuple, of type (string, string, number)
//
const mapToArray: Array<[string, string, number]> = testArray.map(([str, num]):[string, string, number] => [str, str, num]);