About the asserts feature:
https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html#assertion-functions
microsoft/TypeScript#32695

Basically I would like to change:

into this:

function internal(value: any, message?: string | Error): asserts value;

Since this TypeScript feature has been released only recently, how should this best be added to the types without breaking compilation on older TypeScript versions?

cc @Flarna @rbuckton @jstewmon (This is obviously not the complete list of authors because I didn't want to ping too many people. While browsing the source these names came up. Please ping anyone who you think should be involved in the discussion)