Added: cssnext now throw an error if used as a webpack loader to prevent unexpected usage with a recommendation for

Close #61

Author: MoOx

CHANGELOG.md

@@ -1,3 +1,8 @@
+- Added: cssnext now throw an error if used as a webpack loader to prevent
+unexpected usage with a recommendation for
+[cssnext-loader](https://github.com/cssnext/cssnext-loader)
+([#61](https://github.com/cssnext/cssnext/issues/61))
+
 # 1.8.0 - 2015-06-29
 
 - Fixed: replacement of `postcss-log-warnings` (deprecated) by `postcss-reporter`

src/__tests__/prevent-webpack-usage.js

@@ -0,0 +1,51 @@
+const test = require("tape")
+
+import {join as joinPath, dirname} from "path"
+
+import webpack from "webpack"
+
+test("cssnext-loader recommendation", function(t) {
+  webpack(
+    {
+      entry: {
+        "prevent-webpack-usage": [
+          // we don't care about what file is being used
+          // because this should throw an error before the input being used
+          "./package.json",
+        ],
+      },
+      output: {
+        // we don't care about the output...
+        path: "./dist/__tests__/",
+        filename: "prevent-webpack-usage.tmp-webpack-bundle.js",
+      },
+      module: {
+        loaders: [
+          {
+            test: /\.json$/,
+            // use directly cssnext index.js
+            loader: joinPath(dirname(__filename), "..", "index.js"),
+          },
+        ],
+      },
+    },
+    (err, stats) => {
+      if (err) {
+        throw err
+      }
+
+      if (!stats.hasErrors()) {
+        t.fail(
+          "doesn't throw an error if cssnext is used directly as webpack loader"
+        )
+      }
+      else {
+        t.ok(
+          stats.compilation.errors[0].message.indexOf("cssnext-loader") > -1,
+          "should recommand cssnext-loader"
+        )
+      }
+
+      t.end()
+    })
+})

src/index.js

@@ -18,6 +18,18 @@ import optionMessages from "./option.messages"
  * @return {String} if string is given, or {Object} (postcss instance)
  */
 function cssnext(string, options) {
+  // prevent usage as a webpack loader
+  // webpack run loader as function with an object as context
+  // this object contains a "webpack" key set to true if used as a loader
+  // https://github.com/cssnext/cssnext/issues/61
+  if (typeof this === "object" && this.webpack === true) {
+    throw new Error(
+      "⚠︎ Don't use directly cssnext as a webpack loader. " +
+      "Please use `cssnext-loader` instead: " +
+      "https://github.com/cssnext/cssnext-loader"
+    )
+  }
+
   if (arguments.length === 0) {
     options = {}
   }