Force Override Declarations Types

Search Terms

declaration
module
merging
override
interface

Suggestion

Add a way to force override declarations for modules in the workspace. Typescript allows you to create a global.d.ts to add global declarations. How about an override.d.ts or an *.override.d.ts file to override existing modules declarations in the user workspace.

Use Cases

Lets say you install a node module package and type. You see that the type parameter isn't type safe so you use declaration merging to create a more type safe declaration. However, when you use the module type as a variables type or choose to extending it, it automatically uses the types folder declaration first since the type parameter used fits the node_modules declaration type parameter, however that type would not fit the type parameter the user created. This is because declaration merging selects the most appropriate types in order. If the type was to not match the first declaration type it would move on until reaching the appropriate type, which wouldn't work in this use case.

Examples

// Node Module module declaration file
declare module "react-router" {
  interface RouteComponentProps<Params extends { [K in keyof Params]?: string | undefined }> {
    params: Params;
  }
}

// User Defined Type declaration file
export type NoRequired<T extends {}> = {
  [C in keyof T]: T[C] extends Required<T>[C] ? never : T[C];
};

declare module "react-router" {
  interface RouteComponentProps<Params extends NoRequired<Params> }> {
    params: Params;
  }
}

// Using the Interface
import { RouteComponentProps } from "react-router";

// I don't want to extend RouteComponentProps<{ page: string }>, but I can.
export interface CRUDComponentProps
  extends RouteComponentProps<{ page: string }> {
  serverName: string;
  clientName: string;
}

As you can see the type is accepted as the node modules declaration type instead of a user defined declaration type. There no other way of overriding it other than removing it manually from the the node_modules type file.

Checklist

My suggestion meets these guidelines:

• A way of force overriding a type (preferably an override.d.ts or an *.override.d.ts file)
• A way to sort the order in which declaration merging happens

Start with the issue's global.d.ts, proposed override.d.ts or *.override.d.ts patterns, and the react-router declaration-merging example. Review how module declarations are selected and merged, then determine the required behavior for workspace overrides and declaration ordering. Done would require an agreed design plus coverage for the proposed override behavior.