perf: avoid duplicate linting when used with eslint-loader

Author: yyx990803

Diff for: lib/loaders/pitcher.js

@@ -10,7 +10,15 @@ module.exports = code => code
 // and transform it into appropriate requests.
 module.exports.pitch = function (remainingRequest) {
   const query = qs.parse(this.resourceQuery.slice(1))
-  const loaders = this.loaders.slice(1) // remove self
+
+  // if this is a language block request, remove eslint-loader to avoid
+  // duplicate linting.
+  const loaders = query.type
+    ? this.loaders.filter(l => !/(\/|\\|@)eslint-loader/.test(l.path))
+    : this.loaders
+
+  // remove self
+  loaders.shift()
 
   // do not inject if user uses null-loader to void the type (#1239)
   if (loaders.some(l => /(\/|\\|@)null-loader/.test(l.path))) {