feat(webpack-plugin): webpack 5 configuration factory

packages/plugin/webpack/src/Config.ts

@@ -1,4 +1,5 @@
-import { Configuration as WebpackConfiguration } from 'webpack';
+import { Configuration as RawWebpackConfiguration } from 'webpack';
+import { ConfigurationFactory as WebpackConfigurationFactory } from './WebpackConfig';
 
 export interface WebpackPluginEntryPoint {
   /**
@@ -133,3 +134,5 @@ export interface WebpackPluginConfig {
   devServer?: Record<string, unknown>;
   // TODO: use webpack-dev-server.Configuration when @types/webpack-dev-server upgrades to v4
 }
+
+export type WebpackConfiguration = RawWebpackConfiguration | WebpackConfigurationFactory;

packages/plugin/webpack/src/WebpackConfig.ts

@@ -5,12 +5,18 @@ import webpack, { Configuration, WebpackPluginInstance } from 'webpack';
 import { merge as webpackMerge } from 'webpack-merge';
 import { WebpackPluginConfig, WebpackPluginEntryPoint, WebpackPreloadEntryPoint } from './Config';
 import AssetRelocatorPatch from './util/AssetRelocatorPatch';
+import processConfig from './util/processConfig';
 
 type EntryType = string | string[] | Record<string, string | string[]>;
 type WebpackMode = 'production' | 'development';
 
 const d = debug('electron-forge:plugin:webpack:webpackconfig');
 
+export type ConfigurationFactory = (
+  env: string | Record<string, string | boolean | number> | unknown,
+  args: Record<string, unknown>
+) => Configuration | Promise<Configuration>;
+
 export default class WebpackConfigGenerator {
   private isProd: boolean;
 
@@ -32,15 +38,26 @@ export default class WebpackConfigGenerator {
     d('Config mode:', this.mode);
   }
 
-  resolveConfig(config: Configuration | string): Configuration {
-    if (typeof config === 'string') {
-      // eslint-disable-next-line @typescript-eslint/no-var-requires, import/no-dynamic-require, global-require
-      return require(path.resolve(this.projectDir, config)) as Configuration;
-    }
+  async resolveConfig(config: Configuration | ConfigurationFactory | string): Promise<Configuration> {
+    const rawConfig =
+      typeof config === 'string'
+        ? // eslint-disable-next-line import/no-dynamic-require, global-require, @typescript-eslint/no-var-requires
+          (require(path.resolve(this.projectDir, config)) as Configuration | ConfigurationFactory)
+        : config;
 
-    return config;
+    return processConfig(this.preprocessConfig, rawConfig);
   }
 
+  // Users can override this method in a subclass to provide custom logic or
+  // configuration parameters.
+  preprocessConfig = async (config: ConfigurationFactory): Promise<Configuration> =>
+    config(
+      {},
+      {
+        mode: this.mode,
+      }
+    );
+
   get mode(): WebpackMode {
     return this.isProd ? 'production' : 'development';
   }
@@ -102,8 +119,8 @@ export default class WebpackConfigGenerator {
     return defines;
   }
 
-  getMainConfig(): Configuration {
-    const mainConfig = this.resolveConfig(this.pluginConfig.mainConfig);
+  async getMainConfig(): Promise<Configuration> {
+    const mainConfig = await this.resolveConfig(this.pluginConfig.mainConfig);
 
     if (!mainConfig.entry) {
       throw new Error('Required option "mainConfig.entry" has not been defined');
@@ -142,7 +159,7 @@ export default class WebpackConfigGenerator {
   }
 
   async getPreloadRendererConfig(parentPoint: WebpackPluginEntryPoint, entryPoint: WebpackPreloadEntryPoint): Promise<Configuration> {
-    const rendererConfig = this.resolveConfig(entryPoint.config || this.pluginConfig.renderer.config);
+    const rendererConfig = await this.resolveConfig(entryPoint.config || this.pluginConfig.renderer.config);
     const prefixedEntries = entryPoint.prefixedEntries || [];
 
     return webpackMerge(
@@ -165,7 +182,7 @@ export default class WebpackConfigGenerator {
   }
 
   async getRendererConfig(entryPoints: WebpackPluginEntryPoint[]): Promise<Configuration> {
-    const rendererConfig = this.resolveConfig(this.pluginConfig.renderer.config);
+    const rendererConfig = await this.resolveConfig(this.pluginConfig.renderer.config);
     const entry: webpack.Entry = {};
     for (const entryPoint of entryPoints) {
       const prefixedEntries = entryPoint.prefixedEntries || [];

packages/plugin/webpack/src/WebpackPlugin.ts

@@ -249,7 +249,7 @@ the generated files). Instead, it is ${JSON.stringify(pj.main)}`);
       tab = logger.createTab('Main Process');
     }
     await asyncOra('Compiling Main Process Code', async () => {
-      const mainConfig = this.configGenerator.getMainConfig();
+      const mainConfig = await this.configGenerator.getMainConfig();
       await new Promise((resolve, reject) => {
         const compiler = webpack(mainConfig);
         const [onceResolve, onceReject] = once(resolve, reject);

packages/plugin/webpack/src/util/processConfig.ts

@@ -0,0 +1,18 @@
+import { Configuration } from 'webpack';
+import { ConfigurationFactory } from '../WebpackConfig';
+
+const trivialConfigurationFactory =
+  (config: Configuration): ConfigurationFactory =>
+  () =>
+    config;
+
+export type ConfigProcessor = (config: ConfigurationFactory) => Promise<Configuration>;
+
+// Ensure processing logic is run for both `Configuration` and
+// `ConfigurationFactory` config variants.
+const processConfig = async (processor: ConfigProcessor, config: Configuration | ConfigurationFactory): Promise<Configuration> => {
+  const configFactory = typeof config === 'function' ? config : trivialConfigurationFactory(config);
+  return processor(configFactory);
+};
+
+export default processConfig;

packages/plugin/webpack/test/AssetRelocatorPatch_spec.ts

@@ -132,7 +132,7 @@ describe('AssetRelocatorPatch', () => {
     const generator = new WebpackConfigGenerator(config, appPath, false, 3000);
 
     it('builds main', async () => {
-      await asyncWebpack(generator.getMainConfig());
+      await asyncWebpack(await generator.getMainConfig());
 
       await expectOutputFileToHaveTheCorrectNativeModulePath({
         outDir: mainOut,
@@ -186,7 +186,7 @@ describe('AssetRelocatorPatch', () => {
     let generator = new WebpackConfigGenerator(config, appPath, true, 3000);
 
     it('builds main', async () => {
-      const mainConfig = generator.getMainConfig();
+      const mainConfig = await generator.getMainConfig();
       await asyncWebpack(mainConfig);
 
       await expectOutputFileToHaveTheCorrectNativeModulePath({

packages/plugin/webpack/test/WebpackConfig_spec.ts

@@ -1,9 +1,9 @@
-import { Compiler, Entry, WebpackPluginInstance } from 'webpack';
+import { Compiler, Entry, WebpackPluginInstance, Configuration } from 'webpack';
 import { expect } from 'chai';
 import path from 'path';
 
-import WebpackConfigGenerator from '../src/WebpackConfig';
-import { WebpackPluginConfig, WebpackPluginEntryPoint } from '../src/Config';
+import WebpackConfigGenerator, { ConfigurationFactory } from '../src/WebpackConfig';
+import { WebpackPluginConfig, WebpackPluginEntryPoint, WebpackConfiguration } from '../src/Config';
 import AssetRelocatorPatch from '../src/util/AssetRelocatorPatch';
 
 const mockProjectDir = process.platform === 'win32' ? 'C:\\path' : '/path';
@@ -14,6 +14,17 @@ function hasAssetRelocatorPatchPlugin(plugins?: WebpackPlugin[]): boolean {
   return (plugins || []).some((plugin: WebpackPlugin) => plugin instanceof AssetRelocatorPatch);
 }
 
+const sampleWebpackConfig = {
+  module: {
+    rules: [
+      {
+        test: /\.(png|jpg|gif|webp)$/,
+        use: 'file-loader',
+      },
+    ],
+  },
+};
+
 describe('WebpackConfigGenerator', () => {
   describe('rendererTarget', () => {
     it('is web if undefined', () => {
@@ -154,12 +165,12 @@ describe('WebpackConfigGenerator', () => {
   });
 
   describe('getMainConfig', () => {
-    it('fails when there is no mainConfig.entry', () => {
+    it('fails when there is no mainConfig.entry', async () => {
       const config = {
         mainConfig: {},
       } as WebpackPluginConfig;
       const generator = new WebpackConfigGenerator(config, '/', false, 3000);
-      expect(() => generator.getMainConfig()).to.throw('Required option "mainConfig.entry" has not been defined');
+      await expect(generator.getMainConfig()).to.be.rejectedWith('Required option "mainConfig.entry" has not been defined');
     });
 
     it('generates a development config', async () => {
@@ -245,6 +256,40 @@ describe('WebpackConfigGenerator', () => {
       const webpackConfig = await generator.getMainConfig();
       expect(webpackConfig.entry).to.equal(path.resolve(baseDir, 'foo/main.js'));
     });
+
+    it('generates a config from function', async () => {
+      const generateWebpackConfig = (webpackConfig: WebpackConfiguration) => {
+        const config = {
+          mainConfig: webpackConfig,
+          renderer: {
+            entryPoints: [] as WebpackPluginEntryPoint[],
+          },
+        } as WebpackPluginConfig;
+        const generator = new WebpackConfigGenerator(config, mockProjectDir, false, 3000);
+        return generator.getMainConfig();
+      };
+
+      const modelWebpackConfig = await generateWebpackConfig({
+        entry: 'main.js',
+        ...sampleWebpackConfig,
+      });
+
+      // Check fn form
+      expect(
+        await generateWebpackConfig(() => ({
+          entry: 'main.js',
+          ...sampleWebpackConfig,
+        }))
+      ).to.deep.equal(modelWebpackConfig);
+
+      // Check promise form
+      expect(
+        await generateWebpackConfig(async () => ({
+          entry: 'main.js',
+          ...sampleWebpackConfig,
+        }))
+      ).to.deep.equal(modelWebpackConfig);
+    });
   });
 
   describe('getPreloadRendererConfig', () => {
@@ -469,5 +514,121 @@ describe('WebpackConfigGenerator', () => {
       const webpackConfig = await generator.getRendererConfig(config.renderer.entryPoints);
       expect(webpackConfig.target).to.equal('web');
     });
+
+    it('generates a config from function', async () => {
+      const generateWebpackConfig = (webpackConfig: WebpackConfiguration) => {
+        const config = {
+          renderer: {
+            config: webpackConfig,
+            entryPoints: [
+              {
+                name: 'main',
+                js: 'rendererScript.js',
+              },
+            ],
+          },
+        } as WebpackPluginConfig;
+        const generator = new WebpackConfigGenerator(config, mockProjectDir, false, 3000);
+        return generator.getRendererConfig(config.renderer.entryPoints);
+      };
+
+      const modelWebpackConfig = await generateWebpackConfig({
+        ...sampleWebpackConfig,
+      });
+
+      // Check fn form
+      expect(
+        await generateWebpackConfig(() => ({
+          ...sampleWebpackConfig,
+        }))
+      ).to.deep.equal(modelWebpackConfig);
+
+      // Check promise form
+      expect(
+        await generateWebpackConfig(async () => ({
+          ...sampleWebpackConfig,
+        }))
+      ).to.deep.equal(modelWebpackConfig);
+    });
+  });
+
+  describe('preprocessConfig', () => {
+    context('when overriden in subclass', () => {
+      const makeSubclass = () => {
+        let invoked = 0;
+
+        class MyWebpackConfigGenerator extends WebpackConfigGenerator {
+          preprocessConfig = async (config: ConfigurationFactory): Promise<Configuration> => {
+            invoked += 1;
+            return config({ hello: 'world' }, {});
+          };
+        }
+
+        return {
+          getInvokedCounter: () => invoked,
+          MyWebpackConfigGenerator,
+        };
+      };
+
+      it('is not invoked for object config', async () => {
+        const { MyWebpackConfigGenerator, getInvokedCounter } = makeSubclass();
+
+        const config = {
+          mainConfig: {
+            entry: 'main.js',
+            ...sampleWebpackConfig,
+          },
+          renderer: {
+            config: { ...sampleWebpackConfig },
+            entryPoints: [
+              {
+                name: 'main',
+                js: 'rendererScript.js',
+              },
+            ],
+          },
+        } as WebpackPluginConfig;
+
+        const generator = new MyWebpackConfigGenerator(config, mockProjectDir, false, 3000);
+
+        expect(getInvokedCounter()).to.equal(0);
+
+        await generator.getMainConfig();
+        expect(getInvokedCounter()).to.equal(1);
+
+        await generator.getRendererConfig(config.renderer.entryPoints);
+        expect(getInvokedCounter()).to.equal(2);
+      });
+
+      it('is invoked for fn config', async () => {
+        const { MyWebpackConfigGenerator, getInvokedCounter } = makeSubclass();
+
+        const config = {
+          mainConfig: () => ({
+            entry: 'main.js',
+            ...sampleWebpackConfig,
+          }),
+          renderer: {
+            config: () => ({ ...sampleWebpackConfig }),
+            entryPoints: [
+              {
+                name: 'main',
+                js: 'rendererScript.js',
+              },
+            ],
+          },
+        } as WebpackPluginConfig;
+
+        const generator = new MyWebpackConfigGenerator(config, mockProjectDir, false, 3000);
+
+        expect(getInvokedCounter()).to.equal(0);
+
+        await generator.getMainConfig();
+        expect(getInvokedCounter()).to.equal(1);
+
+        await generator.getRendererConfig(config.renderer.entryPoints);
+        expect(getInvokedCounter()).to.equal(2);
+      });
+    });
   });
 });