feat: add support to spawn multiple compilers with different configs (#1765)

Author: anshumanv

packages/webpack-cli/README.md

@@ -37,7 +37,7 @@ yarn add webpack-cli --dev
 
 ```
   --entry string[]         The entry point(s) of your application.
-  -c, --config string      Provide path to a webpack configuration file
+  -c, --config string[]    Provide path to webpack configuration file(s)
   --config-name string[]   Name of the configuration to use
   -m, --merge string       Merge a configuration file using webpack-merge
   --progress               Print compilation progress during build

packages/webpack-cli/lib/groups/ConfigGroup.js

@@ -143,18 +143,34 @@ class ConfigGroup extends GroupHelper {
 
     async resolveConfigFiles() {
         const { config, mode } = this.args;
-        if (config) {
-            const configPath = resolve(process.cwd(), config);
-            const configFiles = getConfigInfoFromFileName(configPath);
-            if (!configFiles.length) {
-                throw new ConfigError(`The specified config file doesn't exist in ${configPath}`);
+        if (config.length > 0) {
+            const resolvedOptions = [];
+            const finalizedConfigs = config.map(async (webpackConfig) => {
+                const configPath = resolve(webpackConfig);
+                const configFiles = getConfigInfoFromFileName(configPath);
+                if (!configFiles.length) {
+                    throw new ConfigError(`The specified config file doesn't exist in ${configPath}`);
+                }
+                const foundConfig = configFiles[0];
+                const resolvedConfig = this.requireConfig(foundConfig);
+                return this.finalize(resolvedConfig);
+            });
+            // resolve all the configs
+            for await (const resolvedOption of finalizedConfigs) {
+                if (Array.isArray(resolvedOption.options)) {
+                    resolvedOptions.push(...resolvedOption.options);
+                } else {
+                    resolvedOptions.push(resolvedOption.options);
+                }
             }
-            const foundConfig = configFiles[0];
-            const resolvedConfig = this.requireConfig(foundConfig);
-            this.opts = await this.finalize(resolvedConfig);
+            // When the resolved configs are more than 1, then pass them as Array [{...}, {...}] else pass the first config object {...}
+            const finalOptions = resolvedOptions.length > 1 ? resolvedOptions : resolvedOptions[0] || {};
+
+            this.opts['options'] = finalOptions;
             return;
         }
 
+        // When no config is supplied, lookup for default configs
         const defaultConfigFiles = getDefaultConfigFiles();
         const tmpConfigFiles = defaultConfigFiles.filter((file) => {
             return existsSync(file.path);
@@ -175,9 +191,8 @@ class ConfigGroup extends GroupHelper {
 
     async resolveConfigMerging() {
         // eslint-disable-next-line no-prototype-builtins
-        if (Object.keys(this.args).some((arg) => arg === 'merge')) {
-            const { merge } = this.args;
-
+        const { merge } = this.args;
+        if (merge) {
             // try resolving merge config
             const newConfigPath = this.resolveFilePath(merge);
 
@@ -189,7 +204,17 @@ class ConfigGroup extends GroupHelper {
             const foundConfig = configFiles[0];
             const resolvedConfig = this.requireConfig(foundConfig);
             const newConfigurationsObject = await this.finalize(resolvedConfig);
-            this.opts['options'] = webpackMerge(this.opts['options'], newConfigurationsObject.options);
+            let resolvedOptions = this.opts['options'];
+            let mergedOptions;
+            if (Array.isArray(resolvedOptions)) {
+                mergedOptions = [];
+                resolvedOptions.forEach((resolvedOption) => {
+                    mergedOptions.push(webpackMerge(resolvedOption, newConfigurationsObject.options));
+                });
+            } else {
+                mergedOptions = webpackMerge(resolvedOptions, newConfigurationsObject.options);
+            }
+            this.opts['options'] = mergedOptions;
         }
     }
 

packages/webpack-cli/lib/utils/cli-flags.js

@@ -91,8 +91,9 @@ const core = [
         usage: '--config <path to webpack configuration file>',
         alias: 'c',
         type: String,
-        defaultValue: null,
+        defaultValue: [],
         group: CONFIG_GROUP,
+        multiple: true,
         description: 'Provide path to a webpack configuration file e.g. ./webpack.config.js',
         link: 'https://webpack.js.org/configuration/',
     },

…tiple/all/.webpack/webpack.config.dev.js …aults/all/.webpack/webpack.config.dev.jstest/config/multiple/all/.webpack/webpack.config.dev.js renamed to test/config/defaults/all/.webpack/webpack.config.dev.js test/config/multiple/all/.webpack/webpack.config.dev.js renamed to test/config/defaults/all/.webpack/webpack.config.dev.js

@@ -3,7 +3,7 @@ const { stat } = require('fs');
 const { resolve } = require('path');
 const { run } = require('../../../utils/test-utils');
 
-describe('multiple config files', () => {
+describe('Default configuration files: ', () => {
     it('Uses prod config from dot folder if present', (done) => {
         const { stdout, stderr } = run(__dirname, [], false);
         expect(stderr).toBeFalsy();