TS trap for corrupted *.d.ts files

README.md

I had to be creative with TypeScript to prevent a common problem in our codebase, where we can't validate our *.d.ts files through skipLibCheck: false and a type (Action) sometimes become any...

ensureActionTypeIsValid.ts

/**
 * This is a TypeScript trap that ensures Action is not corrupted.
 *
 * The problem: since we can't leverage TS lib check, we are completely blind about the validity of
 * the type of the actions. A slight oversight in the d.ts files results in Action being `any` without
 * us noticing it.
 *
 * The solution: this harmless function lets TS throw in case of mistakes in the d.ts files with the
 * following error
 *
 * > Type 'boolean' is not assignable to type 'never'.
 *
 * as a result, the Developer introducing the regression is instantaneously prompted, protecting us.
 */
type ActionTypeIsValid = any extends uui.domain.actions.Action ? never : true

export function ensureActionTypeIsValid(): ActionTypeIsValid {
  // If TS throws, chances are you removed/renamed an action incorrectly
  return true
}