Refactor (#3382)

* refactor: Make instantiatePreprocessor work with cache and log all errors

* refactor: use reduce() to create preprocessors Array

Author: anthony-redFox

lib/preprocessor.js

@@ -54,7 +54,10 @@ function createPriorityPreprocessor (config, preprocessorPriority, basePath, inj
       return
     }
 
-    let p
+    let p = instances[name]
+    if (p) {
+      return p
+    }
 
     try {
       p = injector.get('preprocessor:' + name)
@@ -68,6 +71,14 @@ function createPriorityPreprocessor (config, preprocessorPriority, basePath, inj
       emitter.emit('load_error', 'preprocessor', name)
     }
 
+    if (!p && !alreadyDisplayedErrors[name]) {
+      alreadyDisplayedErrors[name] = true
+      log.error(`Failed to instantiate preprocessor ${name}`)
+      emitter.emit('load_error', 'preprocessor', name)
+    } else {
+      instances[name] = p
+    }
+
     return p
   }
 
@@ -107,31 +118,20 @@ function createPriorityPreprocessor (config, preprocessorPriority, basePath, inj
         })
 
         // Apply preprocessor priority.
-        let sortedPreprocessorNames = preprocessorNames
+        const preprocessors = preprocessorNames
           .map((name) => [name, preprocessorPriority[name] || 0])
           .sort((a, b) => b[1] - a[1])
           .map((duo) => duo[0])
+          .reduce((res, name) => {
+            const p = instantiatePreprocessor(name)
 
-        let preprocessors = []
-        sortedPreprocessorNames.forEach((name) => {
-          const p = instances[name] || instantiatePreprocessor(name)
-
-          if (p == null) {
-            if (!alreadyDisplayedErrors[name]) {
-              alreadyDisplayedErrors[name] = true
-              log.error(`Failed to instantiate preprocessor ${name}`)
-              emitter.emit('load_error', 'preprocessor', name)
+            if (!isBinary || (p && p.handleBinaryFiles)) {
+              res.push(p)
+            } else {
+              log.warn(`Ignored preprocessing ${file.originalPath} because ${name} has handleBinaryFiles=false.`)
             }
-            return
-          }
-
-          instances[name] = p
-          if (!isBinary || p.handleBinaryFiles) {
-            preprocessors.push(p)
-          } else {
-            log.warn(`Ignored preprocessing ${file.originalPath} because ${name} has handleBinaryFiles=false.`)
-          }
-        })
+            return res
+          }, [])
 
         runProcessors(preprocessors, file, isBinary ? buffer : buffer.toString()).then(done, done)
       })