Environment variables in the Feature type

[RomanYarik]

After a discussion made with @nadavwix and @barak007 we need the environments variables infrastructure as a part of the feature declaration. A new Entity will be defined: EnvironmentVariable. It will have a mandatory property of the default value, and optionally a serializer function, for cases we need to serialize the string value to a different one. it will have the following interface:

interface IEnvironmentVariable<T> {
  default: T;
  serializer?: (stringValue: string) => T;
}

And the usage will be as follows:

export default new Feature({
    id: 'myFeature',
    api: {
        myVariable: new EnvironmentVariable({ default: 'value' }).defineEntity(processingEnv),
        mySecondVariable: new EnvironmentVariable({ default: 5, serializer: (raw: string) => parseInt(stringArg) }).defineEntity(mainEnv) 
    },
    dependencies: [],
})

These arguments could be used in the feature.environment setup file as follows:

MyFeature.setup(mainEnv, ({ mySecondVariable }) => {
    document.body.innerText = JSON.stringify(mySecondVariable.getValue())
}

The appropriate cli call will look as follows: yarn start -f my-feature --myFeature.mySecondVariable 8

@nadavwix @AviVahl @barak007 please share your thought on this

[nadavwix]

this looks great, i'd just add a description field so it can show up in help

[barak007]

After meeting conclusions:

1. Config will be able to represent primitive value like string/number/...
2. CLI tools (Application) can override config by passing cli arguments in this format:

• --MyFeature.configKey
• --MyFeature.configKey.configValue

Phase 2: Engine will expose auto cli application that is composed by Feature capabilities.