fix(index): emit warnings as an instance of {Error}

src/Warning.js

@@ -0,0 +1,14 @@
+class Warning extends Error {
+  constructor (warning) {
+    super()
+
+    const { line, column, text } = warning
+
+    this.name = 'LoaderWarning'
+    this.message = `\n(${line}:${column}) ${text}\n`
+
+    this.stack = false
+  }
+}
+
+module.exports = Warning

src/index.js

@@ -10,7 +10,9 @@ const validateOptions = require('schema-utils')
 const postcss = require('postcss')
 const postcssrc = require('postcss-load-config')
 
-const SyntaxError = require('./Error')
+const Warning = require('./Warning.js')
+const SyntaxError = require('./Error.js')
+const parseOptions = require('./options.js')
 
 /**
  * PostCSS Loader
@@ -143,7 +145,9 @@ module.exports = function loader (css, map, meta) {
     return postcss(plugins)
       .process(css, options)
       .then((result) => {
-        result.warnings().forEach((msg) => this.emitWarning(msg.toString()))
+        result.warnings().forEach((warning) => {
+          this.emitWarning(new Warning(warning))
+        })
 
         result.messages.forEach((msg) => {
           if (msg.type === 'dependency') this.addDependency(msg.file)

test/Warnings.test.js

@@ -0,0 +1,33 @@
+const { webpack } = require('@webpack-utilities/test')
+
+const plugin = (options = {}) => (css, result) => {
+  css.walkDecls((node) => {
+    node.warn(result, '<Message>')
+  })
+}
+
+describe('Warnings', () => {
+  test('Plugins', () => {
+    const config = {
+      loader: {
+        test: /\.css$/,
+        options: {
+          plugins: [
+            plugin()
+          ]
+        }
+      }
+    }
+
+    return webpack('css/index.js', config).then((stats) => {
+      const warning = stats.compilation.warnings[0]
+
+      const message = warning.message
+        .split('\n')
+        .slice(1)
+        .join('\n')
+
+      expect(message).toMatchSnapshot()
+    })
+  })
+})

test/__snapshots__/Warnings.test.js.snap

@@ -0,0 +1,7 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`Warnings Plugins 1`] = `
+"
+(1:5) <Message>
+"
+`;