feat: shareable webpack configs using extends

packages/webpack-cli/src/types.ts

@@ -178,6 +178,7 @@ type WebpackDevServerOptions = DevServerConfig &
     config: string[];
     configName?: string[];
     disableInterpret?: boolean;
+    extends?: string[];
     argv: Argv;
   };
 
@@ -186,8 +187,10 @@ type Callback<T extends unknown[]> = (...args: T) => void;
 /**
  * Webpack
  */
-
-type WebpackConfiguration = Configuration;
+type WebpackConfiguration = Configuration & {
+  // TODO add extends to webpack types
+  extends?: string | string[];
+};
 type ConfigOptions = PotentialPromise<WebpackConfiguration | CallableOption>;
 type CallableOption = (env: Env | undefined, argv: Argv) => WebpackConfiguration;
 type WebpackCompiler = Compiler | MultiCompiler;

packages/webpack-cli/src/webpack-cli.ts

@@ -975,6 +975,18 @@ class WebpackCLI implements IWebpackCLI {
         description: "Stop webpack-cli process with non-zero exit code on warnings from webpack",
         helpLevel: "minimum",
       },
+      {
+        name: "extends",
+        alias: "e",
+        configs: [
+          {
+            type: "string",
+          },
+        ],
+        multiple: true,
+        description: "Extend webpack configuration",
+        helpLevel: "minimum",
+      },
     ];
 
     const minimumHelpFlags = [
@@ -1929,6 +1941,86 @@ class WebpackCLI implements IWebpackCLI {
       }
     }
 
+    const flattenConfigs = async (
+      configPaths: string | string[],
+    ): Promise<WebpackConfiguration> => {
+      configPaths = Array.isArray(configPaths) ? configPaths : [configPaths];
+
+      // fetch configs by path
+      const configs = await Promise.all(
+        configPaths.map((configPath: string) =>
+          loadConfigByPath(path.resolve(configPath), options.argv),
+        ),
+      );
+
+      // extract options from configs
+      const extendedConfigOptions = configs.map((extendedConfig) =>
+        Array.isArray(extendedConfig.options) ? extendedConfig.options : [extendedConfig.options],
+      );
+
+      // recursively flatten the configs by looking for extends property
+      for (let i = 0; i < extendedConfigOptions.length; i++) {
+        const extendedConfigs = extendedConfigOptions[i];
+        for (let j = 0; j < extendedConfigs.length; j++) {
+          const extendedConfig = extendedConfigs[j] as WebpackConfiguration;
+          if (extendedConfig.extends) {
+            const flattenedExtendedConfig = await flattenConfigs(extendedConfig.extends);
+            extendedConfigOptions[i][j] = webpackMerge(flattenedExtendedConfig, extendedConfig);
+          }
+        }
+      }
+
+      const flattenedConfigs = extendedConfigOptions.reduce(
+        (acc: Array<ConfigOptions>, options) => {
+          acc.push(options[0]);
+          return acc;
+        },
+        [],
+      );
+
+      const merge = await this.tryRequireThenImport<typeof webpackMerge>("webpack-merge");
+      const mergedConfig = flattenedConfigs.reduce((accumulator: object, options) => {
+        return merge(accumulator, options);
+      }, {});
+
+      delete (mergedConfig as WebpackConfiguration).extends;
+      return mergedConfig;
+    };
+
+    // extends param in CLI gets priority over extends in config file
+    if (options.extends && options.extends.length > 0) {
+      // load the config from the extends option
+      const extendedConfig = await flattenConfigs(options.extends);
+
+      const merge = await this.tryRequireThenImport<typeof webpackMerge>("webpack-merge");
+
+      config.options = Array.isArray(config.options) ? config.options : [config.options];
+
+      // merge extended config with all configs
+      config.options = config.options.map((options) => {
+        return merge(extendedConfig, options);
+      });
+    }
+    // if no extends option is passed, check if the config file has extends
+    else if (
+      (!Array.isArray(config.options) && config.options.extends) ||
+      (Array.isArray(config.options) && config.options.some((options) => options.extends))
+    ) {
+      config.options = Array.isArray(config.options) ? config.options : [config.options];
+
+      const merge = await this.tryRequireThenImport<typeof webpackMerge>("webpack-merge");
+
+      for (let index = 0; index < config.options.length; index++) {
+        const configOptions = config.options[index];
+        if (configOptions.extends) {
+          const extendedConfig = await flattenConfigs(configOptions.extends);
+
+          config.options[index] = merge(extendedConfig, configOptions);
+          delete config.options[index].extends;
+        }
+      }
+    }
+
     if (options.merge) {
       const merge = await this.tryRequireThenImport<typeof webpackMerge>("webpack-merge");
 

test/build/extends/extends-cli-option/base.webpack.config.js

@@ -0,0 +1,9 @@
+module.exports = () => {
+  console.log("base.webpack.config.js");
+
+  return {
+    name: "base_config",
+    mode: "development",
+    entry: "./src/index.js",
+  };
+};

test/build/extends/extends-cli-option/src/index.js

@@ -0,0 +1 @@
+console.log("i am index.js")

test/build/extends/extends-cli-option/webpack.config.js

@@ -0,0 +1,9 @@
+const WebpackCLITestPlugin = require("../../../utils/webpack-cli-test-plugin");
+
+module.exports = () => {
+  console.log("derived.webpack.config.js");
+
+  return {
+    plugins: [new WebpackCLITestPlugin()],
+  };
+};

test/build/extends/extends.test.js

@@ -0,0 +1,68 @@
+"use strict";
+
+const { run } = require("../../utils/test-utils");
+
+describe("extends property", () => {
+  it("extends a provided webpack config correctly", async () => {
+    const { exitCode, stderr, stdout } = await run(__dirname + "/simple-case");
+
+    expect(exitCode).toBe(0);
+    expect(stderr).toBeFalsy();
+    expect(stdout).toContain("base.webpack.config.js");
+    expect(stdout).toContain("derived.webpack.config.js");
+    expect(stdout).toContain("name: 'base_config'");
+    expect(stdout).toContain("mode: 'development'");
+  });
+
+  it("extends a provided array of webpack configs correctly", async () => {
+    const { exitCode, stderr, stdout } = await run(__dirname + "/multiple-extends");
+
+    expect(exitCode).toBe(0);
+    expect(stderr).toBeFalsy();
+    expect(stdout).toContain("base1.webpack.config.js");
+    expect(stdout).toContain("base2.webpack.config.js");
+    expect(stdout).toContain("derived.webpack.config.js");
+    expect(stdout).toContain("name: 'base_config2'");
+    expect(stdout).toContain("mode: 'production'");
+  });
+
+  it("extends a multilevel config correctly", async () => {
+    const { exitCode, stderr, stdout } = await run(__dirname + "/multi-level-extends");
+
+    expect(exitCode).toBe(0);
+    expect(stderr).toBeFalsy();
+    expect(stdout).toContain("base1.webpack.config.js");
+    expect(stdout).toContain("base2.webpack.config.js");
+    expect(stdout).toContain("derived.webpack.config.js");
+    expect(stdout).toContain("name: 'base_config1'");
+    expect(stdout).toContain("mode: 'production'");
+  });
+
+  it("extends a provided webpack config passed in the cli correctly", async () => {
+    const { exitCode, stderr, stdout } = await run(__dirname + "/extends-cli-option", [
+      "--extends",
+      "./base.webpack.config.js",
+    ]);
+
+    expect(exitCode).toBe(0);
+    expect(stderr).toBeFalsy();
+    expect(stdout).toContain("base.webpack.config.js");
+    expect(stdout).toContain("derived.webpack.config.js");
+    expect(stdout).toContain("name: 'base_config'");
+    expect(stdout).toContain("mode: 'development'");
+  });
+
+  it("extends a provided webpack config for multiple configs correctly", async () => {
+    const { exitCode, stderr, stdout } = await run(__dirname + "/multiple-configs");
+
+    expect(exitCode).toBe(0);
+    expect(stderr).toBeFalsy();
+    expect(stdout).toContain("base.webpack.config.js");
+    expect(stdout).toContain("derived.webpack.config.js");
+    expect(stdout).toContain("name: 'derived_config1'");
+    expect(stdout).toContain("name: 'derived_config2'");
+    expect(stdout).not.toContain("name: 'base_config'");
+    expect(stdout).toContain("mode: 'development'");
+    expect(stdout).toContain("topLevelAwait: true");
+  });
+});

test/build/extends/multi-level-extends/base1.webpack.config.js

@@ -0,0 +1,13 @@
+module.exports = () => {
+  console.log("base1.webpack.config.js");
+
+  return {
+    name: "base_config1",
+    extends: ["./base2.webpack.config.js"],
+    mode: "production",
+    entry: "./src/index1.js",
+    output: {
+      filename: "bundle1.js",
+    },
+  };
+};

test/build/extends/multi-level-extends/base2.webpack.config.js

@@ -0,0 +1,9 @@
+module.exports = () => {
+  console.log("base2.webpack.config.js");
+
+  return {
+    name: "base_config2",
+    mode: "development",
+    entry: "./src/index2.js",
+  };
+};

test/build/extends/multi-level-extends/src/index1.js

@@ -0,0 +1 @@
+console.log("i am index1");

test/build/extends/multi-level-extends/webpack.config.js

@@ -0,0 +1,10 @@
+const WebpackCLITestPlugin = require("../../../utils/webpack-cli-test-plugin");
+
+module.exports = () => {
+  console.log("derived.webpack.config.js");
+
+  return {
+    extends: ["./base1.webpack.config.js"],
+    plugins: [new WebpackCLITestPlugin()],
+  };
+};

test/build/extends/multiple-configs/base.webpack.config.js

@@ -0,0 +1,15 @@
+const WebpackCLITestPlugin = require("../../../utils/webpack-cli-test-plugin");
+
+module.exports = () => {
+  console.log("base.webpack.config.js");
+
+  return {
+    name: "base_config",
+    mode: "development",
+    plugins: [new WebpackCLITestPlugin()],
+
+    experiments: {
+      topLevelAwait: true,
+    },
+  };
+};

test/build/extends/multiple-configs/src/index1.js

@@ -0,0 +1 @@
+console.log("i am index1.js");

test/build/extends/multiple-configs/src/index2.js

@@ -0,0 +1 @@
+console.log("i am index2.js");

test/build/extends/multiple-configs/webpack.config.js

@@ -0,0 +1,16 @@
+module.exports = () => {
+  console.log("derived.webpack.config.js");
+
+  return [
+    {
+      name: "derived_config1",
+      extends: "./base.webpack.config.js",
+      entry: "./src/index1.js",
+    },
+    {
+      name: "derived_config2",
+      extends: "./base.webpack.config.js",
+      entry: "./src/index2.js",
+    },
+  ];
+};

test/build/extends/multiple-extends/base1.webpack.config.js

@@ -0,0 +1,9 @@
+module.exports = () => {
+  console.log("base1.webpack.config.js");
+
+  return {
+    name: "base_config1",
+    mode: "development",
+    entry: "./src/index.js",
+  };
+};

test/build/extends/multiple-extends/base2.webpack.config.js

@@ -0,0 +1,9 @@
+module.exports = () => {
+  console.log("base2.webpack.config.js");
+
+  return {
+    name: "base_config2",
+    mode: "production",
+    entry: "./src/index2.js",
+  };
+};

test/build/extends/multiple-extends/src/index2.js

@@ -0,0 +1 @@
+console.log("i am index2");

test/build/extends/multiple-extends/webpack.config.js

@@ -0,0 +1,10 @@
+const WebpackCLITestPlugin = require("../../../utils/webpack-cli-test-plugin");
+
+module.exports = () => {
+  console.log("derived.webpack.config.js");
+
+  return {
+    extends: ["./base1.webpack.config.js", "./base2.webpack.config.js"],
+    plugins: [new WebpackCLITestPlugin()],
+  };
+};

test/build/extends/simple-case/base.webpack.config.js

@@ -0,0 +1,9 @@
+module.exports = () => {
+  console.log("base.webpack.config.js");
+
+  return {
+    name: "base_config",
+    mode: "development",
+    entry: "./src/index.js",
+  };
+};

test/build/extends/simple-case/src/index.js

@@ -0,0 +1 @@
+console.log("index.js")

test/build/extends/simple-case/webpack.config.js

@@ -0,0 +1,10 @@
+const WebpackCLITestPlugin = require("../../../utils/webpack-cli-test-plugin");
+
+module.exports = () => {
+  console.log("derived.webpack.config.js");
+
+  return {
+    extends: "./base.webpack.config.js",
+    plugins: [new WebpackCLITestPlugin()],
+  };
+};