fix: revert ESM dynamic import, require less >= 4.6.3

less@4.6.3 ships a pre-built CJS bundle (dist/less-node.cjs) and maps
the "require" exports condition to it, resolving the ESM/CJS interop
issue that prompted the dynamic import workaround in #578.

Revert getLessImplementation back to synchronous require() and restore
the standard test:only script. Update peer dependency to require
less >= 4.6.3 on the 4.x line.

Source map improvements introduced in #578 (sourceMapBasepath,
disableSourcemapAnnotation, normalizeSourceMap) are preserved.

Author: lemachadoh

babel.config.js

@@ -12,7 +12,6 @@ module.exports = (api) => {
           targets: {
             node: "18.12.0",
           },
-          exclude: ["transform-dynamic-import"],
         },
       ],
     ],

package-lock.json

@@ -38,7 +38,7 @@
     "fix:js": "npm run lint:js -- --fix",
     "fix:prettier": "npm run lint:prettier -- --write",
     "fix": "npm-run-all -l fix:js fix:prettier",
-    "test:only": "node --experimental-vm-modules node_modules/jest-cli/bin/jest.js",
+    "test:only": "cross-env NODE_ENV=test jest",
     "test:watch": "npm run test:only -- --watch",
     "test:coverage": "npm run test:only -- --collectCoverageFrom=\"src/**/*.js\" --coverage",
     "pretest": "npm run lint",
@@ -61,7 +61,7 @@
     "eslint-config-webpack": "^4.5.1",
     "husky": "^9.1.3",
     "jest": "^30.0.0",
-    "less": "^4.6.2",
+    "less": "^4.6.3",
     "less-plugin-glob": "^3.0.0",
     "lint-staged": "^15.2.7",
     "memfs": "^4.9.3",

package.json

@@ -15,7 +15,7 @@ async function lessLoader(source) {
   let implementation;
 
   try {
-    implementation = await getLessImplementation(this, options.implementation);
+    implementation = getLessImplementation(this, options.implementation);
   } catch (error) {
     callback(error);
 

src/index.js

@@ -223,19 +223,20 @@ function normalizeSourceMap(map) {
 
   newMap.sourceRoot = "";
 
-  // `less` (old versions) returns POSIX paths, that's why we need to transform them back to native paths.
+  // `less` returns POSIX paths, that's why we need to transform them back to native paths.
+
   newMap.sources = newMap.sources.map((source) => path.normalize(source));
 
   return newMap;
 }
 
-async function getLessImplementation(loaderContext, implementation) {
+function getLessImplementation(loaderContext, implementation) {
   let resolvedImplementation = implementation;
 
   if (!implementation || typeof implementation === "string") {
     const lessImplPkg = implementation || "less";
 
-    resolvedImplementation = (await import(lessImplPkg)).default;
+    resolvedImplementation = require(lessImplPkg);
   }
 
   return resolvedImplementation;

src/utils.js

@@ -48,7 +48,7 @@ exports[`"sourceMap" options should generate source maps when value has "false"
 #it-works {
   margin: 10px;
 }
-"
+/*# sourceMappingURL=source-map.css.map */"
 `;
 
 exports[`"sourceMap" options should generate source maps when value has "false" value, but the "lessOptions.sourceMap.outputSourceFiles" is "true": errors 1`] = `[]`;
@@ -60,8 +60,8 @@ exports[`"sourceMap" options should generate source maps when value has "false"
   "names": [],
   "sourceRoot": "",
   "sources": [
-    "test/fixtures/node_modules/some/module.less",
-    "test/fixtures/source-map.less",
+    "node_modules/some/module.less",
+    "source-map.less",
   ],
   "sourcesContent": [
     ".modules-dir-some-module {

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

@@ -1,39 +1,36 @@
 import path from "path";
+import less from "less";
 
-export default async () => {
-  const less = (await import("less")).default;
-
-  class Plugin extends less.FileManager {
-    supports(filename) {
-      if (filename === 'forFileLoaderPluginResolve.less') {
-        return true;
-      }
-
-      if (filename === "https://fonts.googleapis.com/css?family=Roboto:500") {
-        return true;
-      }
-
-      return false;
+class Plugin extends less.FileManager {
+  supports(filename) {
+    if (filename === 'forFileLoaderPluginResolve.less') {
+      return true;
+    }
+    
+    if (filename === "https://fonts.googleapis.com/css?family=Roboto:500") {
+      return true;
     }
 
-    loadFile(filename, ...args) {
-      let result;
-
-      if (filename === 'forFileLoaderPluginResolve.less') {
-        result = path.resolve(__dirname, '../', 'file-load-replacement.less');
-      } else if (filename === "https://fonts.googleapis.com/css?family=Roboto:500") {
-        result = path.resolve(__dirname, '../', 'mock-fonts.less');
-      }
-
-      return super.loadFile(result, ...args);
-    };
+    return false;
   }
 
-  class CustomFileLoaderPlugin {
-    install(less, pluginManager) {
-      pluginManager.addFileManager(new Plugin());
+  loadFile(filename, ...args) {
+    let result;
+    
+    if (filename === 'forFileLoaderPluginResolve.less') {
+      result = path.resolve(__dirname, '../', 'file-load-replacement.less');
+    } else if (filename === "https://fonts.googleapis.com/css?family=Roboto:500") {
+      result = path.resolve(__dirname, '../', 'mock-fonts.less');
     }
+
+    return super.loadFile(result, ...args);
+  };
+}
+
+class CustomFileLoaderPlugin {
+  install(less, pluginManager) {
+    pluginManager.addFileManager(new Plugin());
   }
+}
 
-  return CustomFileLoaderPlugin;
-};
+module.exports = CustomFileLoaderPlugin;

test/fixtures/folder/customFileLoaderPlugin.js

@@ -1,6 +1,8 @@
 import fs from "node:fs";
 import path from "node:path";
 
+import less from "less";
+
 const pathMap = {
   "some/css.css": path.resolve(
     __dirname,
@@ -141,6 +143,37 @@ const pathMap = {
   "3rd/b.less": path.resolve(__dirname, "..", "fixtures", "3rd", "b.less"),
 };
 
+class ResolvePlugin extends less.FileManager {
+  supports(filename) {
+    if (filename[0] === "/" || path.win32.isAbsolute(filename)) {
+      return true;
+    }
+
+    if (this.isPathAbsolute(filename)) {
+      return false;
+    }
+
+    return true;
+  }
+
+  supportsSync() {
+    return false;
+  }
+
+  async loadFile(filename, ...args) {
+    const result =
+      pathMap[filename] || path.resolve(__dirname, "..", "fixtures", filename);
+
+    return super.loadFile(result, ...args);
+  }
+}
+
+class CustomImportPlugin {
+  install(lessInstance, pluginManager) {
+    pluginManager.addFileManager(new ResolvePlugin());
+  }
+}
+
 async function getCodeFromLess(testId, options = {}, context = {}) {
   let pathToFile;
 
@@ -186,40 +219,6 @@ async function getCodeFromLess(testId, options = {}, context = {}) {
     ...lessOptions,
   };
 
-  const less = (await import("less")).default;
-
-  class ResolvePlugin extends less.FileManager {
-    supports(filename) {
-      if (filename[0] === "/" || path.win32.isAbsolute(filename)) {
-        return true;
-      }
-
-      if (this.isPathAbsolute(filename)) {
-        return false;
-      }
-
-      return true;
-    }
-
-    supportsSync() {
-      return false;
-    }
-
-    async loadFile(filename, ...args) {
-      const result =
-        pathMap[filename] ||
-        path.resolve(__dirname, "..", "fixtures", filename);
-
-      return super.loadFile(result, ...args);
-    }
-  }
-
-  class CustomImportPlugin {
-    install(lessInstance, pluginManager) {
-      pluginManager.addFileManager(new ResolvePlugin());
-    }
-  }
-
   mergedOptions.plugins.unshift(new CustomImportPlugin());
 
   return less.render(data.toString(), mergedOptions);

test/helpers/getCodeFromLess.js

@@ -9,10 +9,9 @@ import {
 
 describe('"implementation" option', () => {
   it("should work", async () => {
-    const less = (await import("less")).default;
     const testId = "./basic.less";
     const compiler = getCompiler(testId, {
-      implementation: less,
+      implementation: require("less"),
     });
     const stats = await compile(compiler);
     const codeFromBundle = getCodeFromBundle(stats, compiler);
@@ -26,9 +25,8 @@ describe('"implementation" option', () => {
 
   it("should work when implementation option is string", async () => {
     const testId = "./basic.less";
-
     const compiler = getCompiler(testId, {
-      implementation: "less",
+      implementation: require.resolve("less"),
     });
     const stats = await compile(compiler);
     const codeFromBundle = getCodeFromBundle(stats, compiler);

test/implementation.test.js

@@ -14,6 +14,8 @@ import {
   validateDependencies,
 } from "./helpers";
 
+const CustomFileLoaderPlugin = require("./fixtures/folder/customFileLoaderPlugin");
+
 const nodeModulesPath = path.resolve(__dirname, "fixtures", "node_modules");
 
 jest.setTimeout(30000);
@@ -105,11 +107,6 @@ describe("loader", () => {
   });
 
   it("should work third-party plugins as fileLoader", async () => {
-    const getCustomFileLoaderPlugin = (
-      await import("./fixtures/folder/customFileLoaderPlugin")
-    ).default.default;
-    const CustomFileLoaderPlugin = await getCustomFileLoaderPlugin();
-
     const testId = "./file-load.less";
     const compiler = getCompiler(testId, {
       lessOptions: {
@@ -805,9 +802,7 @@ describe("loader", () => {
     let contextInClass = false;
     let contextInObject = false;
 
-    const less = (await import("less")).default;
-
-    class Plugin extends less.FileManager {
+    class Plugin extends require("less").FileManager {
       constructor(less, pluginManager) {
         super();