feat: add loader context in less plugins (#378)

README.md

@@ -476,8 +476,7 @@ module.exports = {
 
 ### Plugins
 
-In order to use [plugins](http://lesscss.org/usage/#plugins), simply set the
-`plugins` option like this:
+In order to use [plugins](http://lesscss.org/usage/#plugins), simply set the `plugins` option like this:
 
 ```js
 // webpack.config.js
@@ -499,6 +498,20 @@ module.exports = {
 };
 ```
 
+> ℹ️ Access to the [loader context](https://webpack.js.org/api/loaders/#the-loader-context) inside the custom plugin can be done using the `less.webpackLoaderContext` property.
+
+```js
+module.exports = {
+  install: function (less, pluginManager, functions) {
+    functions.add('pi', function () {
+      // Loader context is available in `less.webpackLoaderContext`
+
+      return Math.PI;
+    });
+  },
+};
+```
+
 ### Extracting style sheets
 
 Bundling CSS with webpack has some nice advantages like referencing images and fonts with hashed urls or [hot module replacement](https://webpack.js.org/concepts/hot-module-replacement/) in development. In production, on the other hand, it's not a good idea to apply your style sheets depending on JS execution. Rendering may be delayed or even a [FOUC](https://en.wikipedia.org/wiki/Flash_of_unstyled_content) might be visible. Thus it's often still better to have them as separate files in your final production build.

src/utils.js

@@ -166,6 +166,13 @@ function getLessOptions(loaderContext, loaderOptions) {
     lessOptions.plugins.unshift(createWebpackLessPlugin(loaderContext));
   }
 
+  lessOptions.plugins.unshift({
+    install(lessProcessor) {
+      // eslint-disable-next-line no-param-reassign
+      lessProcessor.webpackLoaderContext = loaderContext;
+    },
+  });
+
   const useSourceMap =
     typeof loaderOptions.sourceMap === 'boolean'
       ? loaderOptions.sourceMap

test/__snapshots__/loader.test.js.snap

@@ -511,6 +511,17 @@ exports[`loader should watch imports correctly: errors 1`] = `Array []`;
 
 exports[`loader should watch imports correctly: warnings 1`] = `Array []`;
 
+exports[`loader should work loaderContext in less plugins: css 1`] = `
+".webpackLoaderContext {
+  isDefined: true;
+}
+"
+`;
+
+exports[`loader should work loaderContext in less plugins: errors 1`] = `Array []`;
+
+exports[`loader should work loaderContext in less plugins: warnings 1`] = `Array []`;
+
 exports[`loader should work third-party plugins as fileLoader: css 1`] = `
 ".file-loader {
   background: coral;

test/fixtures/basic-plugins.less

@@ -0,0 +1,5 @@
+@plugin "plugin-1";
+
+.webpackLoaderContext {
+  isDefined: run();
+}

test/fixtures/plugin-1.js

@@ -0,0 +1,11 @@
+registerPlugin({
+  install: function(less, pluginManager, functions) {
+    functions.add('run', function() {
+      if (typeof less.webpackLoaderContext !== 'undefined') {
+        return 'true';
+      }
+
+      return 'false';
+    });
+  }
+})

test/loader.test.js

@@ -727,4 +727,50 @@ describe('loader', () => {
     expect(getWarnings(stats)).toMatchSnapshot('warnings');
     expect(getErrors(stats)).toMatchSnapshot('errors');
   });
+
+  it('should work loaderContext in less plugins', async () => {
+    let contextInClass;
+    let contextInObject;
+
+    // eslint-disable-next-line global-require
+    class Plugin extends require('less').FileManager {
+      constructor(less) {
+        super();
+
+        if (typeof less.webpackLoaderContext !== 'undefined') {
+          contextInClass = true;
+        }
+      }
+    }
+
+    class CustomClassPlugin {
+      // eslint-disable-next-line class-methods-use-this
+      install(less, pluginManager) {
+        pluginManager.addFileManager(new Plugin(less));
+      }
+    }
+
+    const customObjectPlugin = {
+      install(less) {
+        if (typeof less.webpackLoaderContext !== 'undefined') {
+          contextInObject = true;
+        }
+      },
+    };
+
+    const testId = './basic-plugins.less';
+    const compiler = getCompiler(testId, {
+      lessOptions: {
+        plugins: [new CustomClassPlugin(), customObjectPlugin],
+      },
+    });
+    const stats = await compile(compiler);
+    const codeFromBundle = getCodeFromBundle(stats, compiler);
+
+    expect(contextInClass).toBe(true);
+    expect(contextInObject).toBe(true);
+    expect(codeFromBundle.css).toMatchSnapshot('css');
+    expect(getWarnings(stats)).toMatchSnapshot('warnings');
+    expect(getErrors(stats)).toMatchSnapshot('errors');
+  });
 });