[kbn/plugin-helpers/build] copy the public assets of a plugin (#83458)

Co-authored-by: spalger <spalger@users.noreply.github.com>

packages/kbn-plugin-helpers/src/cli.ts

@@ -90,6 +90,7 @@ export function runCli() {
 
         await Tasks.initTargets(context);
         await Tasks.optimize(context);
+        await Tasks.writePublicAssets(context);
         await Tasks.writeServerFiles(context);
         await Tasks.yarnInstall(context);
 

packages/kbn-plugin-helpers/src/integration_tests/build.test.ts

@@ -77,7 +77,8 @@ it('builds a generated plugin into a viable archive', async () => {
      │ info initialized, 0 bundles cached
      │ info starting worker [1 bundle]
      │ succ 1 bundles compiled successfully after <time>
-     info copying source into the build and converting with babel
+     info copying assets from \`public/assets\` to build
+     info copying server source into the build and converting with babel
      info running yarn to install dependencies
      info compressing plugin into [fooTestPlugin-7.5.0.zip]"
   `);

packages/kbn-plugin-helpers/src/tasks/index.ts

@@ -20,5 +20,6 @@
 export * from './clean';
 export * from './create_archive';
 export * from './optimize';
+export * from './write_public_assets';
 export * from './write_server_files';
 export * from './yarn_install';

packages/kbn-plugin-helpers/src/tasks/write_public_assets.ts

@@ -0,0 +1,45 @@
+/*
+ * Licensed to Elasticsearch B.V. under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch B.V. licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+import { pipeline } from 'stream';
+import { promisify } from 'util';
+
+import vfs from 'vinyl-fs';
+
+import { BuildContext } from '../build_context';
+
+const asyncPipeline = promisify(pipeline);
+
+export async function writePublicAssets({ log, plugin, sourceDir, buildDir }: BuildContext) {
+  if (!plugin.manifest.ui) {
+    return;
+  }
+
+  log.info('copying assets from `public/assets` to build');
+
+  await asyncPipeline(
+    vfs.src(['public/assets/**/*'], {
+      cwd: sourceDir,
+      base: sourceDir,
+      buffer: true,
+      allowEmpty: true,
+    }),
+    vfs.dest(buildDir)
+  );
+}

packages/kbn-plugin-helpers/src/tasks/write_server_files.ts

@@ -35,7 +35,7 @@ export async function writeServerFiles({
   buildDir,
   kibanaVersion,
 }: BuildContext) {
-  log.info('copying source into the build and converting with babel');
+  log.info('copying server source into the build and converting with babel');
 
   // copy source files and apply some babel transformations in the process
   await asyncPipeline(