feat: add cli build parallel flag

.changeset/cli-parallel-build-options.md

@@ -0,0 +1,12 @@
+---
+'@backstage/cli': minor
+---
+
+Adds a new `BACKSTAGE_CLI_BUILD_PARELLEL` environment variable to control
+parallelism for some build steps.
+
+This is useful in CI to help avoid out of memory issues when using `terser`. The
+`BACKSTAGE_CLI_BUILD_PARELLEL` environment variable can be set to
+`true | false | [integer]` to override the default behaviour. See
+[terser-webpack-plugin](https://github.com/webpack-contrib/terser-webpack-plugin#parallel)
+for more details.

.github/styles/vocab.txt

@@ -196,6 +196,7 @@ validators
 Voi
 Wealthsimple
 Weaveworks
+Webpack
 xyz
 yaml
 Zalando

packages/cli/package.json

@@ -86,6 +86,7 @@
     "style-loader": "^1.2.1",
     "sucrase": "^3.14.1",
     "tar": "^6.0.1",
+    "terser-webpack-plugin": "^1.4.3",
     "ts-jest": "^26.0.0",
     "ts-loader": "^7.0.4",
     "typescript": "^3.9.3",

packages/cli/src/commands/app/build.ts

@@ -19,6 +19,7 @@ import { loadConfig } from '@backstage/config-loader';
 import { ConfigReader } from '@backstage/config';
 import { paths } from '../../lib/paths';
 import { buildBundle } from '../../lib/bundler';
+import { parseParallel, PARALLEL_ENV_VAR } from '../../lib/parallel';
 
 export default async (cmd: Command) => {
   const appConfigs = await loadConfig({
@@ -27,6 +28,7 @@ export default async (cmd: Command) => {
   });
   await buildBundle({
     entry: 'src/index',
+    parallel: parseParallel(process.env[PARALLEL_ENV_VAR]),
     statsJsonEnabled: cmd.stats,
     config: ConfigReader.fromConfigs(appConfigs),
     appConfigs,

packages/cli/src/commands/backend/buildImage.ts

@@ -14,12 +14,13 @@
  * limitations under the License.
  */
 
+import { Command } from 'commander';
 import fs from 'fs-extra';
 import { join as joinPath, relative as relativePath } from 'path';
 import { createDistWorkspace } from '../../lib/packager';
 import { paths } from '../../lib/paths';
 import { run } from '../../lib/run';
-import { Command } from 'commander';
+import { parseParallel, PARALLEL_ENV_VAR } from '../../lib/parallel';
 
 const PKG_PATH = 'package.json';
 
@@ -41,6 +42,7 @@ export default async (cmd: Command) => {
       ...appConfigs,
       { src: paths.resolveTarget('Dockerfile'), dest: 'Dockerfile' },
     ],
+    parallel: parseParallel(process.env[PARALLEL_ENV_VAR]),
     skeleton: 'skeleton.tar',
   });
   console.log(`Dist workspace ready at ${tempDistWorkspace}`);

packages/cli/src/lib/bundler/optimization.ts

@@ -15,7 +15,9 @@
  */
 
 import { Options } from 'webpack';
+import TerserPlugin from 'terser-webpack-plugin';
 import { BundlingOptions } from './types';
+import { isParallelDefault } from '../parallel';
 
 export const optimization = (
   options: BundlingOptions,
@@ -24,6 +26,16 @@ export const optimization = (
 
   return {
     minimize: !isDev,
+    // Only configure when parallel is explicitly overriden from the default
+    ...(!isParallelDefault(options.parallel)
+      ? {
+          minimizer: [
+            new TerserPlugin({
+              parallel: options.parallel,
+            }),
+          ],
+        }
+      : {}),
     runtimeChunk: 'single',
     splitChunks: {
       automaticNameDelimiter: '-',

packages/cli/src/lib/bundler/types.ts

@@ -16,6 +16,7 @@
 
 import { AppConfig, Config } from '@backstage/config';
 import { BundlingPathsOptions } from './paths';
+import { ParallelOption } from '../parallel';
 
 export type BundlingOptions = {
   checksEnabled: boolean;
@@ -23,6 +24,7 @@ export type BundlingOptions = {
   config: Config;
   appConfigs: AppConfig[];
   baseUrl: URL;
+  parallel?: ParallelOption;
 };
 
 export type BackendBundlingOptions = Omit<BundlingOptions, 'baseUrl'> & {
@@ -37,6 +39,7 @@ export type ServeOptions = BundlingPathsOptions & {
 
 export type BuildOptions = BundlingPathsOptions & {
   statsJsonEnabled: boolean;
+  parallel?: ParallelOption;
   config: Config;
   appConfigs: AppConfig[];
 };

packages/cli/src/lib/packager/index.ts

@@ -20,10 +20,11 @@ import {
   resolve as resolvePath,
   relative as relativePath,
 } from 'path';
+import { tmpdir } from 'os';
+import tar, { CreateOptions } from 'tar';
 import { paths } from '../paths';
 import { run } from '../run';
-import tar, { CreateOptions } from 'tar';
-import { tmpdir } from 'os';
+import { ParallelOption } from '../parallel';
 
 type LernaPackage = {
   name: string;
@@ -58,6 +59,11 @@ type Options = {
    */
   buildDependencies?: boolean;
 
+  /**
+   * Enable (true/false) or control amount of (number) parallelism in some build steps.
+   */
+  parallel?: ParallelOption;
+
   /**
    * If set, creates a skeleton tarball that contains all package.json files
    * with the same structure as the workspace dir.
@@ -85,7 +91,12 @@ export async function createDistWorkspace(
 
   if (options.buildDependencies) {
     const scopeArgs = targets.flatMap(target => ['--scope', target.name]);
-    await run('yarn', ['lerna', 'run', ...scopeArgs, 'build'], {
+    const lernaArgs =
+      options.parallel && Number.isInteger(options.parallel)
+        ? ['--concurrency', options.parallel.toString()]
+        : [];
+
+    await run('yarn', ['lerna', ...lernaArgs, 'run', ...scopeArgs, 'build'], {
       cwd: paths.targetRoot,
     });
   }

packages/cli/src/lib/parallel.test.ts

@@ -0,0 +1,59 @@
+/*
+ * Copyright 2020 Spotify AB
+ *
+ * Licensed 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 { isParallelDefault, parseParallel } from './parallel';
+
+describe('parallel', () => {
+  describe(parseParallel, () => {
+    it('coerces "false" string to boolean', () => {
+      expect(parseParallel('false')).toBeFalsy();
+    });
+
+    it('coerces "true" to boolean', () => {
+      expect(parseParallel('true')).toBeTruthy();
+    });
+
+    it('coerces number string to number', () => {
+      expect(parseParallel('2')).toBe(2);
+    });
+    it.each([[true], [false], [2]])('returns itself for %p', value => {
+      expect(parseParallel(value as any)).toEqual(value);
+    });
+
+    it.each([[undefined], [null]])('returns true for %p', value => {
+      expect(parseParallel(value as any)).toBe(true);
+    });
+
+    it.each([['on'], [2.5], ['2.5']])('throws error for %p', value => {
+      expect(() => parseParallel(value as any)).toThrowError(
+        `Parallel option value '${value}' is not a boolean or integer`,
+      );
+    });
+  });
+
+  describe(isParallelDefault, () => {
+    it('returns true if default value', () => {
+      expect(isParallelDefault(undefined)).toBeTruthy();
+      expect(isParallelDefault(true)).toBeTruthy();
+    });
+
+    it('returns false if not default value', () => {
+      expect(isParallelDefault(false)).toBeFalsy();
+      expect(isParallelDefault(2)).toBeFalsy();
+      expect(isParallelDefault('true' as any)).toBeFalsy();
+    });
+  });
+});

packages/cli/src/lib/parallel.ts

@@ -0,0 +1,47 @@
+/*
+ * Copyright 2020 Spotify AB
+ *
+ * Licensed 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.
+ */
+
+export const PARALLEL_ENV_VAR = 'BACKSTAGE_CLI_BUILD_PARALLEL';
+
+export type ParallelOption = boolean | number | undefined;
+
+export function isParallelDefault(parallel: ParallelOption) {
+  return parallel === undefined || parallel === true;
+}
+
+export function parseParallel(
+  parallel: boolean | string | number | undefined,
+): ParallelOption {
+  if (parallel === undefined || parallel === null) {
+    return true;
+  } else if (typeof parallel === 'boolean') {
+    return parallel;
+  } else if (typeof parallel === 'number' && Number.isInteger(parallel)) {
+    return parallel;
+  } else if (typeof parallel === 'string') {
+    if (parallel === 'true') {
+      return true;
+    } else if (parallel === 'false') {
+      return false;
+    } else if (Number.isInteger(parseFloat(parallel.toString()))) {
+      return Number(parallel);
+    }
+  }
+
+  throw Error(
+    `Parallel option value '${parallel}' is not a boolean or integer`,
+  );
+}

packages/cli/src/types.d.ts

@@ -29,3 +29,5 @@ declare module '@svgr/rollup' {
 }
 
 declare module '@rollup/plugin-yaml';
+
+declare module 'terser-webpack-plugin';