simplify "openFile" and make it async

apps/remix-ide/src/app/files/fileManager.js

@@ -177,7 +177,7 @@ class FileManager extends Plugin {
       }
       await this._handleExists(path, `Cannot open file ${path}`)
       await this._handleIsFile(path, `Cannot open file ${path}`)
-      return this.openFile(path)
+      await this.openFile(path)
     } catch (e) {
       throw new Error(e)
     }
@@ -601,8 +601,11 @@ class FileManager extends Plugin {
     this.events.emit('noFileSelected')
   }
 
-  openFile (file) {
-    const _openFile = (file) => {
+  async openFile (file) {
+    if (!file) {
+      this.emit('noFileSelected')
+      this.events.emit('noFileSelected')
+    } else {
       this.saveCurrentFile()
       let resolved
       try {
@@ -614,9 +617,12 @@ class FileManager extends Plugin {
       const provider = resolved.provider
       this._deps.config.set('currentFile', file)
       this.openedFiles[file] = file
+      await (() => {
+        return new Promise((resolve, reject) => {
           provider.get(file, (error, content) => {
             if (error) {
               console.log(error)
+              reject(error)
             } else {
               if (provider.isReadOnly(file)) {
                 this.editor.openReadOnly(file, content)
@@ -626,13 +632,11 @@ class FileManager extends Plugin {
               // TODO: Only keep `this.emit` (issue#2210)
               this.emit('currentFileChanged', file)
               this.events.emit('currentFileChanged', file)
+              resolve()
             }
           })
-    }
-    if (file) return _openFile(file)
-    else {
-      this.emit('noFileSelected')
-      this.events.emit('noFileSelected')
+        })
+      })()      
     }    
   }