Start services

[streamich]

Summary

Adds createStartServicesGetter utility.

Usage example:

setup(core, plugins) {
  const start = createStartServicesGetter(core.getStartServices);

  plugins.expressions.registerFunction(someCanvasFunction(start));
}

Checklist

Delete any items that are not applicable to this PR.

• Unit or functional tests were updated or added to match the most common scenarios

For maintainers

• This was checked for breaking API changes and was labeled appropriately

[elasticmachine]

Pinging @elastic/kibana-app-arch (Team:AppArch)

[kibanamachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request
• Commit: 4ade32c

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@elasticmachine merge upstream

[lukeelmers]

This LGTM! I tested it in the data plugin (temporarily removing the service getters we were using in getInternalStartServices), and it all worked as expected.

You just have to remember to pass the correct parameters to the CoreSetup generic so that TS doesn't complain:

  public setup(
    core: CoreSetup<DataStartDependencies, DataPublicPluginStart>,
    { expressions, uiActions }: DataSetupDependencies
  ): DataPublicPluginSetup {
    const startServices = createStartServicesGetter(core.getStartServices);

    // ultimately we can just get rid of this function & instead pass `startServices`
    const getInternalStartServices: GetInternalStartServicesFn = () => {
      const { core: coreStart, self } = startServices();
      return {
        fieldFormats: self.fieldFormats,
        notifications: coreStart.notifications,
      };
    };
    // ...etc
  }

One pattern we could discuss as a next step is how we want to pass down a single service, in cases where we want to be explicit about which start services are actually required by a component. But IMO this solves the overarching problem in the simplest way possible.

[streamich]

One pattern we could discuss as a next step is how we want to pass down a single service, in cases where we want to be explicit about which start services are actually required by a component.

One way is to use casting, this way code stays nice and clean.

interface SomethingParams {
  start: StartServicesGetter<Pick<MyPluginStartDeps, 'data'>>;
}

class Something {
  constructor({ start }: SomethingParams) {
    start().plugins.data.indexPatterns(...)
  }
}

and in plugin itself no changes needed:

setup(core) {
  const start = createStartServicesGetter(core.getStartServices);
  new Something({ start });
}