Implemented more robust module loading (#211)

- added loadModule() utility function
- updated loaders to use new module loading mechanism
- added more entries to gitignore file
- refactored gitignore to be more explicit

.gitignore

@@ -1,3 +1,5 @@
-/node_modules
-dist
-coverage
+/**/dist/
+/.idea/
+/coverage/
+/node_modules/
+/package-lock.json

src/less-loader.js

@@ -1,12 +1,15 @@
-import importCwd from 'import-cwd'
 import pify from 'pify'
 import humanlizePath from './utils/humanlize-path'
+import { loadModule } from './utils/load-module'
 
 export default {
   name: 'less',
   test: /\.less$/,
   async process({ code }) {
-    const less = importCwd('less')
+    const less = loadModule('less')
+    if (!less) {
+      throw new Error(`You need to install "less" packages in order to process Less files`)
+    }
 
     let { css, map, imports } = await pify(less.render.bind(less))(code, {
       ...this.options,

src/sass-loader.js

@@ -1,8 +1,8 @@
 import path from 'path'
 import pify from 'pify'
 import resolve from 'resolve'
-import importCwd from 'import-cwd'
 import PQueue from 'p-queue'
+import { loadModule } from './utils/load-module'
 
 // This queue makes sure node-sass leaves one thread available for executing fs tasks
 // See: https://github.com/sass/node-sass/issues/857
@@ -18,15 +18,15 @@ const getUrlOfPartial = url => {
 
 const resolvePromise = pify(resolve)
 
+// List of supported SASS modules in the order of preference
+const sassModuleIds = ['node-sass', 'sass']
+
 export default {
   name: 'sass',
-  test: /\.s[ac]ss$/,
+  test: /\.(sass|scss)$/,
   process({ code }) {
     return new Promise((resolve, reject) => {
-      const sass = importCwd.silent('node-sass') || importCwd.silent('sass')
-      if (!sass) {
-        throw new Error(`You need to install either node-sass or sass in order to process Sass files`)
-      }
+      const sass = loadSassOrThrow()
       const render = pify(sass.render.bind(sass))
       return workQueue.add(() =>
         render({
@@ -90,3 +90,20 @@ export default {
     })
   }
 }
+
+function loadSassOrThrow() {
+  // Loading one of the supported modules
+  for (const moduleId of sassModuleIds) {
+    const module = loadModule(moduleId)
+    if (module) {
+      return module
+    }
+  }
+
+  // Throwing exception if module can't be loaded
+  throw new Error(
+    `You need to install one of the following packages: ` +
+    sassModuleIds.map(moduleId => `"${moduleId}"`).join(', ') + ' ' +
+    `in order to process SASS files`
+  )
+}

src/stylus-loader.js

@@ -1,11 +1,14 @@
-import importCwd from 'import-cwd'
 import pify from 'pify'
+import { loadModule } from './utils/load-module'
 
 export default {
   name: 'stylus',
   test: /\.(styl|stylus)$/,
   async process({ code }) {
-    const stylus = importCwd('stylus')
+    const stylus = loadModule('stylus')
+    if (!stylus) {
+      throw new Error(`You need to install "stylus" packages in order to process Stylus files`)
+    }
 
     const style = stylus(code, {
       ...this.options,

src/utils/load-module.js

@@ -0,0 +1,12 @@
+import importCwd from 'import-cwd'
+
+export function loadModule(moduleId) {
+  // Trying to load module normally (relative to plugin directory)
+  const path = require.resolve(moduleId)
+  if (path) {
+    return require(path)
+  }
+
+  // Then, trying to load it relative to CWD
+  return importCwd.silent(moduleId)
+}