From @HitalloExiled on September 4, 2018 17:33

• VSCode Version: 1.26.1
• OS Version: Windows 10

Steps to Reproduce:

//index.ts
export default function foo(): void;
export default function foo(bar: string): void;
export default function foo(bar?: string): void
{ }

Does this issue occur when all extensions are disabled?: Yes

Copied from original issue: microsoft/vscode#57889