Initializing `let` variables and exhaustiveness checking

[rauschma]

let tagName;
switch (kind) {
  case ListKind.Ordered:
    tagName = 'ol';
    break;
  case ListKind.Unordered:
    tagName = 'ul';
    break;
  default:
    assertNever(kind);
}

• The inferred type of tagName is string|undefined, but should be string, AFAICT.
• Similarly: If I give tagName the type string, I get the error: “Variable 'tagName' is used before being assigned”.

[ajafff]

Control flow analysis does not know that assertNever never returns. You need to return or throw assertNever(kind); to end the control flow.

[rauschma]

That makes sense! Thanks!