feat: allow to use String value for the implementation option

README.md

@@ -56,7 +56,7 @@ And run `webpack` via your preferred method.
 |  **[`additionalData`](#additionalData)**  | `{String\|Function}` |       `undefined`        | Prepends/Appends `Less` code to the actual entry file. |
 |       **[`sourceMap`](#sourcemap)**       |     `{Boolean}`      |    `compiler.devtool`    | Enables/Disables generation of source maps.            |
 | **[`webpackImporter`](#webpackimporter)** |     `{Boolean}`      |          `true`          | Enables/Disables the default Webpack importer.         |
-|  **[`implementation`](#implementation)**  |      `{Object}`      |          `less`          | Setup Less implementation to use.                      |
+|  **[`implementation`](#implementation)**  |  `{Object\|String}`  |          `less`          | Setup Less implementation to use.                      |
 
 ### `lessOptions`
 
@@ -316,14 +316,16 @@ module.exports = {
 
 ### `implementation`
 
-Type: `Object`
+Type: `Object | String`
 
 > ⚠ less-loader compatible with Less 3 and 4 versions
 
 The special `implementation` option determines which implementation of Less to use. Overrides the locally installed `peerDependency` version of `less`.
 
 **This option is only really useful for downstream tooling authors to ease the Less 3-to-4 transition.**
 
+#### Object
+
 **webpack.config.js**
 
 ```js
@@ -348,6 +350,32 @@ module.exports = {
 };
 ```
 
+#### String
+
+**webpack.config.js**
+
+```js
+module.exports = {
+  module: {
+    rules: [
+      {
+        test: /\.less$/i,
+        use: [
+          "style-loader",
+          "css-loader",
+          {
+            loader: "less-loader",
+            options: {
+              implementation: require.resolve("less"),
+            },
+          },
+        ],
+      },
+    ],
+  },
+};
+```
+
 ## Examples
 
 ### Normal usage

src/index.js

@@ -1,19 +1,36 @@
 import path from "path";
 
-import less from "less";
-
 import schema from "./options.json";
-import { getLessOptions, isUnsupportedUrl, normalizeSourceMap } from "./utils";
+import {
+  getLessOptions,
+  isUnsupportedUrl,
+  normalizeSourceMap,
+  getLessImplementation,
+} from "./utils";
 import LessError from "./LessError";
 
 async function lessLoader(source) {
   const options = this.getOptions(schema);
   const callback = this.async();
+  const implementation = getLessImplementation(this, options.implementation);
+
+  if (!implementation) {
+    callback(
+      new Error(`The Less implementation "${options.implementation}" not found`)
+    );
+
+    return;
+  }
+
   const webpackContextSymbol = Symbol("loaderContext");
-  const lessOptions = getLessOptions(this, {
-    ...options,
-    webpackContextSymbol,
-  });
+  const lessOptions = getLessOptions(
+    this,
+    {
+      ...options,
+      webpackContextSymbol,
+    },
+    implementation
+  );
   const useSourceMap =
     typeof options.sourceMap === "boolean" ? options.sourceMap : this.sourceMap;
 
@@ -35,7 +52,7 @@ async function lessLoader(source) {
   let result;
 
   try {
-    result = await (options.implementation || less).render(data, lessOptions);
+    result = await implementation.render(data, lessOptions);
   } catch (error) {
     if (error.filename) {
       // `less` returns forward slashes on windows when `webpack` resolver return an absolute windows path in `WebpackFileManager`
@@ -48,7 +65,7 @@ async function lessLoader(source) {
     return;
   }
 
-  delete less[webpackContextSymbol];
+  delete implementation[webpackContextSymbol];
 
   const { css, imports } = result;
 

src/options.json

@@ -35,7 +35,14 @@
     },
     "implementation": {
       "description": "The implementation of the `Less` to be used (https://github.com/webpack-contrib/less-loader#implementation).",
-      "type": "object"
+      "anyOf": [
+        {
+          "type": "string"
+        },
+        {
+          "type": "object"
+        }
+      ]
     }
   },
   "additionalProperties": false

src/utils.js

@@ -1,7 +1,6 @@
 import path from "path";
 import util from "util";
 
-import less from "less";
 import { klona } from "klona/full";
 
 /* eslint-disable class-methods-use-this */
@@ -30,9 +29,10 @@ const MODULE_REQUEST_REGEX = /^[^?]*~/;
  * Creates a Less plugin that uses webpack's resolving engine that is provided by the loaderContext.
  *
  * @param {LoaderContext} loaderContext
+ * @param {object} implementation
  * @returns {LessPlugin}
  */
-function createWebpackLessPlugin(loaderContext) {
+function createWebpackLessPlugin(loaderContext, implementation) {
   const resolve = loaderContext.getResolve({
     dependencyType: "less",
     conditionNames: ["less", "style"],
@@ -42,7 +42,7 @@ function createWebpackLessPlugin(loaderContext) {
     preferRelative: true,
   });
 
-  class WebpackFileManager extends less.FileManager {
+  class WebpackFileManager extends implementation.FileManager {
     supports(filename) {
       if (filename[0] === "/" || IS_NATIVE_WIN32_PATH.test(filename)) {
         return true;
@@ -157,9 +157,10 @@ function createWebpackLessPlugin(loaderContext) {
  *
  * @param {object} loaderContext
  * @param {object} loaderOptions
+ * @param {object} implementation
  * @returns {Object}
  */
-function getLessOptions(loaderContext, loaderOptions) {
+function getLessOptions(loaderContext, loaderOptions, implementation) {
   const options = klona(
     typeof loaderOptions.lessOptions === "function"
       ? loaderOptions.lessOptions(loaderContext) || {}
@@ -180,7 +181,9 @@ function getLessOptions(loaderContext, loaderOptions) {
       : true;
 
   if (shouldUseWebpackImporter) {
-    lessOptions.plugins.unshift(createWebpackLessPlugin(loaderContext));
+    lessOptions.plugins.unshift(
+      createWebpackLessPlugin(loaderContext, implementation)
+    );
   }
 
   lessOptions.plugins.unshift({
@@ -239,4 +242,30 @@ function normalizeSourceMap(map) {
   return newMap;
 }
 
-export { getLessOptions, isUnsupportedUrl, normalizeSourceMap };
+function getLessImplementation(loaderContext, implementation) {
+  let resolvedImplementation = implementation;
+
+  if (!implementation || typeof implementation === "string") {
+    const lessImplPkg = implementation || "less";
+
+    try {
+      // eslint-disable-next-line import/no-dynamic-require, global-require
+      resolvedImplementation = require(lessImplPkg);
+    } catch (error) {
+      loaderContext.emitError(error);
+
+      // eslint-disable-next-line consistent-return
+      return;
+    }
+  }
+
+  // eslint-disable-next-line consistent-return
+  return resolvedImplementation;
+}
+
+export {
+  getLessOptions,
+  isUnsupportedUrl,
+  normalizeSourceMap,
+  getLessImplementation,
+};

test/__snapshots__/implementation.test.js.snap

@@ -1,5 +1,33 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
+exports[`"implementation" option should throw error when unresolved package: errors 1`] = `
+Array [
+  "ModuleBuildError: Module build failed (from \`replaced original path\`):
+Error: The Less implementation \\"unresolved\\" not found",
+  "ModuleError: Module Error (from \`replaced original path\`):
+(Emitted value instead of an instance of Error) Error: Cannot find module 'unresolved' from 'src/utils.js'",
+]
+`;
+
+exports[`"implementation" option should throw error when unresolved package: warnings 1`] = `Array []`;
+
+exports[`"implementation" option should work when implementation option is string: css 1`] = `
+".box {
+  color: #fe33ac;
+  border-color: #fdcdea;
+  background: url(box.png);
+}
+.box div {
+  -webkit-box-shadow: 0 0 5px rgba(0, 0, 0, 0.3);
+  box-shadow: 0 0 5px rgba(0, 0, 0, 0.3);
+}
+"
+`;
+
+exports[`"implementation" option should work when implementation option is string: errors 1`] = `Array []`;
+
+exports[`"implementation" option should work when implementation option is string: warnings 1`] = `Array []`;
+
 exports[`"implementation" option should work: css 1`] = `
 ".box {
   color: #fe33ac;

test/__snapshots__/validate-options.test.js.snap

@@ -60,25 +60,48 @@ exports[`validate options should throw an error on the "additionalData" option w
     * options.additionalData should be an instance of function."
 `;
 
-exports[`validate options should throw an error on the "implementation" option with "false" value 1`] = `
+exports[`validate options should throw an error on the "implementation" option with "() => {}" value 1`] = `
 "Invalid options object. Less Loader has been initialized using an options object that does not match the API schema.
- - options.implementation should be an object:
-   object { … }
-   -> The implementation of the \`Less\` to be used (https://github.com/webpack-contrib/less-loader#implementation)."
+ - options.implementation should be one of these:
+   string | object { … }
+   -> The implementation of the \`Less\` to be used (https://github.com/webpack-contrib/less-loader#implementation).
+   Details:
+    * options.implementation should be a string.
+    * options.implementation should be an object:
+      object { … }"
 `;
 
-exports[`validate options should throw an error on the "implementation" option with "string" value 1`] = `
+exports[`validate options should throw an error on the "implementation" option with "[]" value 1`] = `
 "Invalid options object. Less Loader has been initialized using an options object that does not match the API schema.
- - options.implementation should be an object:
-   object { … }
-   -> The implementation of the \`Less\` to be used (https://github.com/webpack-contrib/less-loader#implementation)."
+ - options.implementation should be one of these:
+   string | object { … }
+   -> The implementation of the \`Less\` to be used (https://github.com/webpack-contrib/less-loader#implementation).
+   Details:
+    * options.implementation should be a string.
+    * options.implementation should be an object:
+      object { … }"
+`;
+
+exports[`validate options should throw an error on the "implementation" option with "false" value 1`] = `
+"Invalid options object. Less Loader has been initialized using an options object that does not match the API schema.
+ - options.implementation should be one of these:
+   string | object { … }
+   -> The implementation of the \`Less\` to be used (https://github.com/webpack-contrib/less-loader#implementation).
+   Details:
+    * options.implementation should be a string.
+    * options.implementation should be an object:
+      object { … }"
 `;
 
 exports[`validate options should throw an error on the "implementation" option with "true" value 1`] = `
 "Invalid options object. Less Loader has been initialized using an options object that does not match the API schema.
- - options.implementation should be an object:
-   object { … }
-   -> The implementation of the \`Less\` to be used (https://github.com/webpack-contrib/less-loader#implementation)."
+ - options.implementation should be one of these:
+   string | object { … }
+   -> The implementation of the \`Less\` to be used (https://github.com/webpack-contrib/less-loader#implementation).
+   Details:
+    * options.implementation should be a string.
+    * options.implementation should be an object:
+      object { … }"
 `;
 
 exports[`validate options should throw an error on the "lessOptions" option with "[]" value 1`] = `

test/implementation.test.js

@@ -23,4 +23,30 @@ describe('"implementation" option', () => {
     expect(getWarnings(stats)).toMatchSnapshot("warnings");
     expect(getErrors(stats)).toMatchSnapshot("errors");
   });
+
+  it("should work when implementation option is string", async () => {
+    const testId = "./basic.less";
+    const compiler = getCompiler(testId, {
+      implementation: require.resolve("less"),
+    });
+    const stats = await compile(compiler);
+    const codeFromBundle = getCodeFromBundle(stats, compiler);
+    const codeFromLess = await getCodeFromLess(testId);
+
+    expect(codeFromBundle.css).toBe(codeFromLess.css);
+    expect(codeFromBundle.css).toMatchSnapshot("css");
+    expect(getWarnings(stats)).toMatchSnapshot("warnings");
+    expect(getErrors(stats)).toMatchSnapshot("errors");
+  });
+
+  it("should throw error when unresolved package", async () => {
+    const testId = "./basic.less";
+    const compiler = getCompiler(testId, {
+      implementation: "unresolved",
+    });
+    const stats = await compile(compiler);
+
+    expect(getWarnings(stats)).toMatchSnapshot("warnings");
+    expect(getErrors(stats)).toMatchSnapshot("errors");
+  });
 });

test/validate-options.test.js

@@ -27,8 +27,8 @@ describe("validate options", () => {
     },
     implementation: {
       // eslint-disable-next-line global-require
-      success: [require("less")],
-      failure: [true, false, "string"],
+      success: [require("less"), "less"],
+      failure: [true, false, () => {}, []],
     },
     unknown: {
       success: [],