[core/api] add name validation in registerFeatureFlag

packages/core/src/api/app/FeatureFlags.tsx

@@ -62,7 +62,7 @@ class FeatureFlagsImpl implements FeatureFlagsApi {
 
     if (!name.match(/^[a-z]+[a-z0-9-]+$/)) {
       errors.push(
-        'The `name` argument must start with a lowercase letter and only contain lowercase letters, numbers and hyphens.' +
+        'The `name` argument must start with a lowercase letter and only contain lowercase letters, numbers and hyphens. ' +
           'Examples: feature-flag-one, alpha, release-2020',
       );
     }

packages/core/src/api/plugin/Plugin.tsx

@@ -21,6 +21,7 @@ import {
   RouteOptions,
   FeatureFlagName,
 } from './types';
+import { FeatureFlags } from '../app/FeatureFlags';
 import { Widget } from '../widgetView/types';
 
 export type PluginConfig = {
@@ -76,6 +77,7 @@ export default class Plugin {
       return [];
     }
 
+    const pluginId = this.getId();
     const outputs = new Array<PluginOutput>();
 
     this.config.register({
@@ -94,6 +96,14 @@ export default class Plugin {
       },
       featureFlags: {
         registerFeatureFlag(name) {
+          const errors = FeatureFlags.checkFeatureFlagNameErrors(name);
+
+          if (errors.length > 0) {
+            throw new Error(
+              `Failed to register '${name}' feature flag in '${pluginId}' plugin: ${errors[0]}`,
+            );
+          }
+
           outputs.push({ type: 'feature-flag', name });
         },
       },