Add support for import overrides

[petermasking]

The repository service controls all application imports. Currently, it returns the actual module or a remote implementation based on the segmentation. The next step is to utilize the repository for providing alternative implementations.

Let's look at a simple example.

export default async function sayHello(): Promise<string>
{
    return 'Hello World';
}

// src/greet.ts
import getMessage from './sayHello';

export default async function greet(): Promise<void>
{
    const message = await getMessage();
    console.log(message); // Hello World
}

All this module does is importing and calling a function from another module. Now suppose we want to replace the sayHello module with the sayBye module, without modifying the greet module. The sayBye module has the same exports.

export default async function sayBye(): Promise<string>
{
    return 'Bye World';
}

For this, we need some way to tell the repository to provide an alternative module when the sayHello module gets requested. The proposed solution is to add an additional property to the repository to configure this.

{
    "url": "http://localhost:3000",
    "repository":
    {
        "overrides":
        {
            "./sayHello": "./sayBye"
        }
    }
}

The overrides property configures the repository to provide the sayBye module when the sayHello module is requested. Thus overriding the actual request. This should work for module imports (like the greet does), and the RPC API.

GET http://localhost:3000/rpc/sayHello HTTP/1.1

This request should result into the 'Bye World' message.