[ResponseOps] Package for feature flags (#185000)

## Summary

This PR creates a package to expose tools for managing feature flags in
the ResponseOps codebase.

Usage:

```
const featureFlagService = createFeatureFlagService(['test.myFeature', 'test.myFeature.subFeature']);


if (featureFlagService.isFeatureFlagSet('test.myFeature')) {
  // my feature code
}
```

The code is typed so if you do
`featureFlagService.isFeatureFlagSet('foo')` and `foo` is not part of
the feature flags set TS will report an error.

### Checklist

Delete any items that are not applicable to this PR.

- [x] [Unit or functional
tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)
were updated or added to match the most common scenarios

### For maintainers

- [x] This was checked for breaking API changes and was [labeled
appropriately](https://www.elastic.co/guide/en/kibana/master/contributing.html#kibana-release-notes-process)

---------

Co-authored-by: kibanamachine <42973632+kibanamachine@users.noreply.github.com>

.github/CODEOWNERS

@@ -681,6 +681,7 @@ packages/kbn-reporting/server @elastic/appex-sharedux
 packages/kbn-resizable-layout @elastic/kibana-data-discovery
 examples/resizable_layout_examples @elastic/kibana-data-discovery
 x-pack/test/plugin_functional/plugins/resolver_test @elastic/security-solution
+packages/response-ops/feature_flag_service @elastic/response-ops
 examples/response_stream @elastic/ml-ui
 packages/kbn-rison @elastic/kibana-operations
 x-pack/plugins/rollup @elastic/kibana-management

package.json

@@ -692,6 +692,7 @@
     "@kbn/resizable-layout": "link:packages/kbn-resizable-layout",
     "@kbn/resizable-layout-examples-plugin": "link:examples/resizable_layout_examples",
     "@kbn/resolver-test-plugin": "link:x-pack/test/plugin_functional/plugins/resolver_test",
+    "@kbn/response-ops-feature-flag-service": "link:packages/response-ops/feature_flag_service",
     "@kbn/response-stream-plugin": "link:examples/response_stream",
     "@kbn/rison": "link:packages/kbn-rison",
     "@kbn/rollup-plugin": "link:x-pack/plugins/rollup",

packages/response-ops/feature_flag_service/README.md

@@ -0,0 +1,27 @@
+# @kbn/response-ops-feature-flags
+
+This packages exposes a feature flag service that is used in the ResponseOps plugins and packages to handle feature flags.
+
+## Usage
+
+### Create feature flag service
+
+```
+const featureFlagService = createFeatureFlagService(['test.myFeature', 'test.myFeature.subFeature']); // TS will infer the types automatically 
+```
+
+or
+
+```
+type FeatureFlagValues = 'test.myFeature' | 'test.myOtherFeature'
+const featureFlagService = createFeatureFlagService<FeatureFlagValues>(['test.myFeature']);
+```
+
+### Checking the existence of a feature flag
+```
+const featureFlagService = createFeatureFlagService(['test.myFeature', 'test.myFeature.subFeature']);
+
+if (featureFlagService.isFeatureFlagSet('test.myFeature')) {
+  // my feature code
+}
+```

packages/response-ops/feature_flag_service/feature_flag_service.test.ts

@@ -0,0 +1,29 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0 and the Server Side Public License, v 1; you may not use this file except
+ * in compliance with, at your election, the Elastic License 2.0 or the Server
+ * Side Public License, v 1.
+ */
+
+import { createFeatureFlagService } from './feature_flag_service';
+
+type FeatureFlagValues = 'test.myFeature' | 'test.myOtherFeature';
+
+describe('FeatureFlagService', () => {
+  it('returns true if the feature exists', () => {
+    const featureFlagService = createFeatureFlagService(['test.myFeature']);
+    expect(featureFlagService.isFeatureFlagSet('test.myFeature')).toBe(true);
+  });
+
+  it('returns false if the feature does not exist', () => {
+    const featureFlagService = createFeatureFlagService(['test.myFeature']);
+    // @ts-expect-error: foo is not part of the valid feature flags
+    expect(featureFlagService.isFeatureFlagSet('foo')).toBe(false);
+  });
+
+  it('returns true if the feature exists (as typed)', () => {
+    const featureFlagService = createFeatureFlagService<FeatureFlagValues>(['test.myFeature']);
+    expect(featureFlagService.isFeatureFlagSet('test.myFeature')).toBe(true);
+  });
+});

packages/response-ops/feature_flag_service/feature_flag_service.ts

@@ -0,0 +1,25 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0 and the Server Side Public License, v 1; you may not use this file except
+ * in compliance with, at your election, the Elastic License 2.0 or the Server
+ * Side Public License, v 1.
+ */
+
+class FeatureFlag<T extends string = string> {
+  private readonly featureFlags = new Set<T>();
+
+  constructor(featureFlags: T[]) {
+    featureFlags.forEach((featureFlag) => this.featureFlags.add(featureFlag));
+  }
+
+  public isFeatureFlagSet(featureFlag: T): boolean {
+    return this.featureFlags.has(featureFlag);
+  }
+}
+
+export const createFeatureFlagService = <T extends string>(featureFlags: T[]) => {
+  return new FeatureFlag<typeof featureFlags[number]>(featureFlags);
+};
+
+export type FeatureFlagService<T extends string = string> = InstanceType<typeof FeatureFlag<T>>;

packages/response-ops/feature_flag_service/index.ts

@@ -0,0 +1,10 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0 and the Server Side Public License, v 1; you may not use this file except
+ * in compliance with, at your election, the Elastic License 2.0 or the Server
+ * Side Public License, v 1.
+ */
+
+export { createFeatureFlagService } from './feature_flag_service';
+export type { FeatureFlagService } from './feature_flag_service';

packages/response-ops/feature_flag_service/jest.config.js

@@ -0,0 +1,13 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0 and the Server Side Public License, v 1; you may not use this file except
+ * in compliance with, at your election, the Elastic License 2.0 or the Server
+ * Side Public License, v 1.
+ */
+
+module.exports = {
+  preset: '@kbn/test/jest_node',
+  rootDir: '../../..',
+  roots: ['<rootDir>/packages/response-ops/feature_flag_service'],
+};

packages/response-ops/feature_flag_service/kibana.jsonc

@@ -0,0 +1,5 @@
+{
+  "type": "shared-common",
+  "id": "@kbn/response-ops-feature-flag-service",
+  "owner": "@elastic/response-ops"
+}

packages/response-ops/feature_flag_service/package.json

@@ -0,0 +1,6 @@
+{
+  "name": "@kbn/response-ops-feature-flag-service",
+  "private": true,
+  "version": "1.0.0",
+  "license": "SSPL-1.0 OR Elastic License 2.0"
+}

packages/response-ops/feature_flag_service/tsconfig.json

@@ -0,0 +1,17 @@
+{
+  "extends": "../../../tsconfig.base.json",
+  "compilerOptions": {
+    "outDir": "target/types",
+    "types": [
+      "jest",
+      "node"
+    ]
+  },
+  "include": [
+    "**/*.ts",
+  ],
+  "exclude": [
+    "target/**/*"
+  ],
+  "kbn_references": []
+}

tsconfig.base.json

@@ -1356,6 +1356,8 @@
       "@kbn/resizable-layout-examples-plugin/*": ["examples/resizable_layout_examples/*"],
       "@kbn/resolver-test-plugin": ["x-pack/test/plugin_functional/plugins/resolver_test"],
       "@kbn/resolver-test-plugin/*": ["x-pack/test/plugin_functional/plugins/resolver_test/*"],
+      "@kbn/response-ops-feature-flag-service": ["packages/response-ops/feature_flag_service"],
+      "@kbn/response-ops-feature-flag-service/*": ["packages/response-ops/feature_flag_service/*"],
       "@kbn/response-stream-plugin": ["examples/response_stream"],
       "@kbn/response-stream-plugin/*": ["examples/response_stream/*"],
       "@kbn/rison": ["packages/kbn-rison"],

yarn.lock

@@ -5880,6 +5880,10 @@
   version "0.0.0"
   uid ""
 
+"@kbn/response-ops-feature-flag-service@link:packages/response-ops/feature_flag_service":
+  version "0.0.0"
+  uid ""
+
 "@kbn/response-stream-plugin@link:examples/response_stream":
   version "0.0.0"
   uid ""