fix: normalize sources in source maps

src/LessError.js

@@ -16,13 +16,13 @@ class LessError extends Error {
     this.hideStack = true;
   }
 
-  static getFileExcerptIfPossible(lessErr) {
-    if (typeof lessErr.extract === 'undefined') {
+  static getFileExcerptIfPossible(lessError) {
+    if (typeof lessError.extract === 'undefined') {
       return [];
     }
 
-    const excerpt = lessErr.extract.slice(0, 2);
-    const column = Math.max(lessErr.column - 1, 0);
+    const excerpt = lessError.extract.slice(0, 2);
+    const column = Math.max(lessError.column - 1, 0);
 
     if (typeof excerpt[0] === 'undefined') {
       excerpt.shift();

src/index.js

@@ -6,10 +6,10 @@ import { getOptions } from 'loader-utils';
 import validateOptions from 'schema-utils';
 
 import schema from './options.json';
-import { getLessOptions, isUnsupportedUrl } from './utils';
+import { getLessOptions, isUnsupportedUrl, normalizeSourceMap } from './utils';
 import LessError from './LessError';
 
-function lessLoader(source) {
+async function lessLoader(source) {
   const options = getOptions(this);
 
   validateOptions(schema, options, {
@@ -19,6 +19,14 @@ function lessLoader(source) {
 
   const callback = this.async();
   const lessOptions = getLessOptions(this, options);
+  const useSourceMap =
+    typeof options.sourceMap === 'boolean' ? options.sourceMap : this.sourceMap;
+
+  if (useSourceMap) {
+    lessOptions.sourceMap = {
+      outputSourceFiles: true,
+    };
+  }
 
   let data = source;
 
@@ -29,30 +37,42 @@ function lessLoader(source) {
         : `${options.additionalData}\n${data}`;
   }
 
-  less
-    .render(data, lessOptions)
-    .then(({ css, map, imports }) => {
-      imports.forEach((item) => {
-        if (isUnsupportedUrl(item)) {
-          return;
-        }
-
-        // `less` return forward slashes on windows when `webpack` resolver return an absolute windows path in `WebpackFileManager`
-        // Ref: https://github.com/webpack-contrib/less-loader/issues/357
-        this.addDependency(path.normalize(item));
-      });
-
-      callback(null, css, typeof map === 'string' ? JSON.parse(map) : map);
-    })
-    .catch((lessError) => {
-      if (lessError.filename) {
-        // `less` return forward slashes on windows when `webpack` resolver return an absolute windows path in `WebpackFileManager`
-        // Ref: https://github.com/webpack-contrib/less-loader/issues/357
-        this.addDependency(path.normalize(lessError.filename));
-      }
-
-      callback(new LessError(lessError));
-    });
+  let result;
+
+  try {
+    result = await less.render(data, lessOptions);
+  } catch (error) {
+    if (error.filename) {
+      // `less` return forward slashes on windows when `webpack` resolver return an absolute windows path in `WebpackFileManager`
+      // Ref: https://github.com/webpack-contrib/less-loader/issues/357
+      this.addDependency(path.normalize(error.filename));
+    }
+
+    callback(new LessError(error));
+
+    return;
+  }
+
+  const { css, imports } = result;
+
+  imports.forEach((item) => {
+    if (isUnsupportedUrl(item)) {
+      return;
+    }
+
+    // `less` return forward slashes on windows when `webpack` resolver return an absolute windows path in `WebpackFileManager`
+    // Ref: https://github.com/webpack-contrib/less-loader/issues/357
+    this.addDependency(path.normalize(item));
+  });
+
+  let map =
+    typeof result.map === 'string' ? JSON.parse(result.map) : result.map;
+
+  if (map && useSourceMap) {
+    map = normalizeSourceMap(map, this.rootContext);
+  }
+
+  callback(null, css, map);
 }
 
 export default lessLoader;

src/utils.js

@@ -11,10 +11,10 @@ const trailingSlash = /[/\\]$/;
 // This somewhat changed in Less 3.x. Now the file name comes without the
 // automatically added extension whereas the extension is passed in as `options.ext`.
 // So, if the file name matches this regexp, we simply ignore the proposed extension.
-const isModuleImport = /^~([^/]+|[^/]+\/|@[^/]+[/][^/]+|@[^/]+\/?|@[^/]+[/][^/]+\/)$/;
+const IS_SPECIAL_MODULE_IMPORT = /^~[^/]+$/;
 
 // `[drive_letter]:\` + `\\[server]\[sharename]\`
-const isNativeWin32Path = /^[a-zA-Z]:[/\\]|^\\\\/i;
+const IS_NATIVE_WIN32_PATH = /^[a-z]:[/\\]|^\\\\/i;
 
 /**
  * Creates a Less plugin that uses webpack's resolving engine that is provided by the loaderContext.
@@ -32,7 +32,7 @@ function createWebpackLessPlugin(loaderContext) {
 
   class WebpackFileManager extends less.FileManager {
     supports(filename) {
-      if (filename[0] === '/' || isNativeWin32Path.test(filename)) {
+      if (filename[0] === '/' || IS_NATIVE_WIN32_PATH.test(filename)) {
         return true;
       }
 
@@ -89,7 +89,7 @@ function createWebpackLessPlugin(loaderContext) {
       let result;
 
       try {
-        if (isModuleImport.test(filename)) {
+        if (IS_SPECIAL_MODULE_IMPORT.test(filename)) {
           const error = new Error();
 
           error.type = 'Next';
@@ -171,23 +171,12 @@ function getLessOptions(loaderContext, loaderOptions) {
     },
   });
 
-  const useSourceMap =
-    typeof loaderOptions.sourceMap === 'boolean'
-      ? loaderOptions.sourceMap
-      : loaderContext.sourceMap;
-
-  if (useSourceMap) {
-    lessOptions.sourceMap = {
-      outputSourceFiles: true,
-    };
-  }
-
   return lessOptions;
 }
 
 function isUnsupportedUrl(url) {
-  // Is Windows paths `c:\`
-  if (/^[a-zA-Z]:\\/.test(url)) {
+  // Is Windows path
+  if (IS_NATIVE_WIN32_PATH.test(url)) {
     return false;
   }
 
@@ -196,4 +185,24 @@ function isUnsupportedUrl(url) {
   return /^[a-zA-Z][a-zA-Z\d+\-.]*:/.test(url);
 }
 
-export { getLessOptions, isUnsupportedUrl };
+function normalizeSourceMap(map) {
+  const newMap = map;
+
+  // map.file is an optional property that provides the output filename.
+  // Since we don't know the final filename in the webpack build chain yet, it makes no sense to have it.
+  // eslint-disable-next-line no-param-reassign
+  delete newMap.file;
+
+  // eslint-disable-next-line no-param-reassign
+  newMap.sourceRoot = '';
+
+  // `less` returns POSIX paths, that's why we need to transform them back to native paths.
+  // eslint-disable-next-line no-param-reassign
+  newMap.sources = newMap.sources.map((source) => {
+    return path.normalize(source);
+  });
+
+  return newMap;
+}
+
+export { getLessOptions, isUnsupportedUrl, normalizeSourceMap };

test/__snapshots__/additionalData-option.test.js.snap

@@ -1,6 +1,6 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
-exports[`additionalData option should work additionalData data as function: css 1`] = `
+exports[`"additionalData" option should work additionalData data as function: css 1`] = `
 "/* RelativePath: additional-data.less; */
 .background {
   color: coral;
@@ -11,17 +11,17 @@ exports[`additionalData option should work additionalData data as function: css
 "
 `;
 
-exports[`additionalData option should work additionalData data as function: errors 1`] = `Array []`;
+exports[`"additionalData" option should work additionalData data as function: errors 1`] = `Array []`;
 
-exports[`additionalData option should work additionalData data as function: warnings 1`] = `Array []`;
+exports[`"additionalData" option should work additionalData data as function: warnings 1`] = `Array []`;
 
-exports[`additionalData option should work additionalData data as string: css 1`] = `
+exports[`"additionalData" option should work additionalData data as string: css 1`] = `
 ".background {
   color: coral;
 }
 "
 `;
 
-exports[`additionalData option should work additionalData data as string: errors 1`] = `Array []`;
+exports[`"additionalData" option should work additionalData data as string: errors 1`] = `Array []`;
 
-exports[`additionalData option should work additionalData data as string: warnings 1`] = `Array []`;
+exports[`"additionalData" option should work additionalData data as string: warnings 1`] = `Array []`;