feat: add support for merging multiple configurations

packages/webpack-cli/README.md

@@ -39,7 +39,7 @@ yarn add webpack-cli --dev
   --entry string[]         The entry point(s) of your application.
   -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
+  -m, --merge              Merge several configurations using webpack-merge
   --progress               Print compilation progress during build
   --color                  Enables colors on console
   --no-color               Disable colors on console

packages/webpack-cli/__tests__/ConfigGroup/ConfigGroup.test.js

@@ -0,0 +1,27 @@
+const ConfigGroup = require('../../lib/groups/ConfigGroup');
+const { resolve } = require('path');
+
+describe('ConfigGroup', function () {
+    it('should handle merge properly', async () => {
+        const group = new ConfigGroup([
+            {
+                merge: true,
+            },
+            {
+                config: [resolve(__dirname, './webpack.config.cjs')],
+            },
+        ]);
+
+        const result = await group.run();
+        const expectedOptions = {
+            output: { filename: './dist-commonjs.js', libraryTarget: 'commonjs' },
+            entry: './a.js',
+            name: 'amd',
+            mode: 'production',
+            devtool: 'eval-cheap-module-source-map',
+            target: 'node',
+        };
+        expect(result.options).toEqual(expectedOptions);
+        expect(result.outputOptions).toEqual({});
+    });
+});

packages/webpack-cli/__tests__/ConfigGroup/webpack.config.cjs

@@ -0,0 +1,21 @@
+module.exports = [
+    {
+        output: {
+            filename: './dist-amd.js',
+            libraryTarget: 'amd',
+        },
+        entry: './a.js',
+        name: 'amd',
+        mode: 'development',
+        devtool: 'eval-cheap-module-source-map',
+    },
+    {
+        output: {
+            filename: './dist-commonjs.js',
+            libraryTarget: 'commonjs',
+        },
+        entry: './a.js',
+        mode: 'production',
+        target: 'node',
+    },
+];

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

@@ -190,30 +190,20 @@ class ConfigGroup extends GroupHelper {
     }
 
     async resolveConfigMerging() {
-        // eslint-disable-next-line no-prototype-builtins
         const { merge } = this.args;
         if (merge) {
-            // try resolving merge config
-            const newConfigPath = this.resolveFilePath(merge);
-
-            if (!newConfigPath) {
-                throw new ConfigError("The supplied merge config doesn't exist.", 'MergeError');
+            // Get the current configuration options
+            const { options: configOptions } = this.opts;
+
+            // we can only merge when there are multiple configurations
+            // either by passing multiple configs by flags or passing a
+            // single config exporting an array
+            if (!Array.isArray(configOptions)) {
+                throw new ConfigError('Atleast two configurations are required for merge.', 'MergeError');
             }
 
-            const configFiles = getConfigInfoFromFileName(newConfigPath);
-            const foundConfig = configFiles[0];
-            const resolvedConfig = this.requireConfig(foundConfig);
-            const newConfigurationsObject = await this.finalize(resolvedConfig);
-            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);
-            }
+            // We return a single config object which is passed to the compiler
+            const mergedOptions = configOptions.reduce((currentConfig, mergedConfig) => webpackMerge(currentConfig, mergedConfig), {});
             this.opts['options'] = mergedOptions;
         }
     }

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

@@ -108,11 +108,11 @@ const core = [
     },
     {
         name: 'merge',
-        usage: '--merge <path to configuration to be merged>',
+        usage: '--merge',
         alias: 'm',
-        type: String,
+        type: Boolean,
         group: CONFIG_GROUP,
-        description: 'Merge a configuration file using webpack-merge e.g. ./webpack.config.js',
+        description: 'Merge two or more configurations using webpack-merge e.g. -c ./webpack.config.js -c ./webpack.test.config.js --merge',
         link: 'https://github.com/survivejs/webpack-merge',
     },
     {

test/help/help-flags.test.js

@@ -17,7 +17,7 @@ describe('commands help', () => {
     it('shows flag help with valid flag', () => {
         const { stdout, stderr } = run(__dirname, ['--help', '--merge'], false);
         expect(stdout).not.toContain(helpHeader);
-        expect(stdout).toContain('webpack -m, --merge <path to configuration to be merged>');
+        expect(stdout).toContain('webpack -m, --merge');
         expect(stderr).toHaveLength(0);
     });
 

test/merge/config-absent/merge-config-absent.test.js

@@ -13,7 +13,7 @@ describe('merge flag configuration', () => {
         // Since the process will exit, nothing on stdout
         expect(stdout).toBeFalsy();
         // Confirm that the user is notified
-        expect(stderr).toContain(`MergeError: The supplied merge config doesn't exist.`);
+        expect(stderr).toContain(`MergeError: Atleast two configurations are required for merge.`);
         // Default config would be used
         expect(fs.existsSync(join(__dirname, './dist/merged.js'))).toBeFalsy();
         // Since the process will exit so no compilation will be done

test/merge/config/merge-config.test.js

@@ -1,27 +1,29 @@
 'use strict';
 
-const { stat } = require('fs');
+const { existsSync } = require('fs');
 const { resolve } = require('path');
 
 const { run } = require('../../utils/test-utils');
 
 describe('merge flag configuration', () => {
-    it('merges two configurations together', (done) => {
-        const { stdout } = run(__dirname, ['--config', './1.js', '--merge', './2.js'], false);
+    it('merges two configurations together', () => {
+        const { stdout, stderr, exitCode } = run(__dirname, ['--config', './1.js', '-c', './2.js', '--merge'], false);
         expect(stdout).not.toContain('option has not been set, webpack will fallback to');
-        stat(resolve(__dirname, './dist/merged.js'), (err, stats) => {
-            expect(err).toBe(null);
-            expect(stats.isFile()).toBe(true);
-            done();
-        });
+        expect(existsSync(resolve(__dirname, './dist/merged.js'))).toBeTruthy();
+        expect(stderr).toBeFalsy();
+        expect(exitCode).toBe(0);
     });
-    it('merges two configurations together with flag alias', (done) => {
-        const { stdout } = run(__dirname, ['--config', './1.js', '-m', './2.js'], false);
+    it('merges two configurations together with flag alias', () => {
+        const { stdout, stderr, exitCode } = run(__dirname, ['--config', './1.js', '--config', './2.js', '-m'], false);
         expect(stdout).toContain('merged.js');
-        stat(resolve(__dirname, './dist/merged.js'), (err, stats) => {
-            expect(err).toBe(null);
-            expect(stats.isFile()).toBe(true);
-            done();
-        });
+        expect(existsSync(resolve(__dirname, './dist/merged.js'))).toBeTruthy();
+        expect(stderr).toBeFalsy();
+        expect(exitCode).toBe(0);
+    });
+    it('fails when there are less than 2 configurations to merge', () => {
+        const { stdout, stderr, exitCode } = run(__dirname, ['--config', './1.js', '-m'], false);
+        expect(stderr).toContain(`MergeError: Atleast two configurations are required for merge.`);
+        expect(stdout).toBeFalsy();
+        expect(exitCode).toBe(2);
     });
 });