TypeScript Version: 3.7 (issue is with lib typing)

Search Terms: regex, matchall, es2020

Code

const matches = Array.from('xxx'.matchAll(/x/g));
matches[0].index; // TS reports index may be undefined, when it should always be defined

Currently matchAll returns an iterable of RegExpMatchArray. However, the index and input properties on RegExpMatchArray are optional because String#match returns a match object without those if the regex has the global flag (#35157).

matchAll on the other hand doesn't have the same behavior, so it should use RegExpExecArray where both of those properties are non-optional (or maybe create a RegExpMatchAllArray type)

> Array.from('xxx'.matchAll(/x/g)) 
[
  [ 'x', index: 0, input: 'xxx', groups: undefined ],
  [ 'x', index: 1, input: 'xxx', groups: undefined ],
  [ 'x', index: 2, input: 'xxx', groups: undefined ]
]
> Array.from('xxx'.matchAll(/a/g)) 
[]
> Array.from('aaa'.matchAll(/x/g)) 
[]

Expected behavior:

input and index on the match objects are not optional

Actual behavior:

TS reports that input and index may be optional

Playground Link: (Can't use playground since lib cannot be configured)

Related Issues: #30936 introduced String#matchAll