fix: warn missing plugin

lib/index.js

@@ -10,9 +10,18 @@ const genStylesCode = require('./codegen/styleInjection')
 const { genHotReloadCode } = require('./codegen/hotReload')
 const genCustomBlocksCode = require('./codegen/customBlocks')
 const componentNormalizerPath = require.resolve('./runtime/componentNormalizer')
+const { NS } = require('./plugin')
 
 module.exports = function (source) {
   const loaderContext = this
+
+  if (!loaderContext[NS]) {
+    loaderContext.emitError(new Error(
+      `vue-loader was used without the corresponding plugin. ` +
+      `Make sure to include VueLoaderPlugin in your webpack config.`
+    ))
+  }
+
   const stringifyRequest = r => loaderUtils.stringifyRequest(loaderContext, r)
 
   const {

lib/plugin.js

+const fs = require('fs')
+const path = require('path')
 const qs = require('querystring')
 const RuleSet = require('webpack/lib/RuleSet')
 
-// TODO handle vueRule with oneOf
-module.exports = class VueLoaderPlugin {
+const id = 'vue-loader-plugin'
+const NS = path.dirname(fs.realpathSync(__filename))
+
+class VueLoaderPlugin {
   apply (compiler) {
+    // add NS marker so that the loader can detect and report missing plugin
+    if (compiler.hooks) {
+      // webpack 4
+      compiler.hooks.compilation.tap(id, compilation => {
+        compilation.hooks.normalModuleLoader.tap(id, loaderContext => {
+          loaderContext[NS] = true
+        })
+      })
+    } else {
+      // webpack < 4
+      compiler.plugin('compilation', compilation => {
+        compilation.plugin('normal-module-loader', loaderContext => {
+          loaderContext[NS] = true
+        })
+      })
+    }
+
     // get a hold of the raw rules
     const rawRules = compiler.options.module.rules
     // use webpack's RuleSet utility to normalize user rules
@@ -175,3 +196,6 @@ function cleanIdent (use) {
   }
   return use
 }
+
+VueLoaderPlugin.NS = NS
+module.exports = VueLoaderPlugin