Error handling and code cleanup

pkg/analysis_server/bin/dartdeps.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import 'dart:async';
 import 'dart:io';
 
 import 'package:args/args.dart';
 import 'package:analysis_server/src/analysis_manager.dart';
 
 /**
  * Start analysis server as a separate process and use the websocket protocol
  * to analyze the application specified on the command line.
  */
 void main(List<String> args) {
-  _DartDependencyAnalyzer analyzer = new _DartDependencyAnalyzer();
-  analyzer.start(args);
+  new _DartDependencyAnalyzer(args).run()
+      .catchError((error, stack) {
+        print('Analysis failed: $error');
+        if (stack != null) {
+          print(stack);
+        }
+      });
 }
 
 /**
  * Instances of [_DartDependencyAnalyzer] launch an analysis server and use
  * that server to analyze the dependencies of an application.
  */
 class _DartDependencyAnalyzer {
   /**
    * The name of the application that is used to start the analyzer.
    */
   static const BINARY_NAME = 'dartdeps';
 
   /**
    * The name of the option used to print usage information.
    */
-  static const String HELP_OPTION = "help";
+  static const String HELP_OPTION = 'help';
 
   /**
    * The name of the option used to specify an already running server.
    */
-  static const String SERVER_OPTION = "server";
+  static const String SERVER_OPTION = 'server';
+
+  /**
+   * The command line arguments.
+   */
+  final List<String> args;
+
+  /**
+   * The manager for the analysis server.
+   */
+  AnalysisManager manager;
+
+  _DartDependencyAnalyzer(this.args);
 
   /**
    * Parse the command line arguments to determine the application to be
    * analyzed, then launch and manage an analysis server to do the work.
-   * If there is a problem with the given arguments, then return a non zero
-   * value, otherwise return zero.
    */
-  void start(List<String> args) {
+  Future run() {
+    return new Future(start).then(analyze).whenComplete(stop);
+  }
+
+  /**
+   * Parse the command line arguments to determine the application to be
+   * analyzed, then launch an analysis server.
+   * Return `null` if the command line arguments are invalid.

[Brian Wilkerson, 2014/02/25 23:36:06]

Do we really want to return null? I would have thought that we wanted to return
a "new Future.value(null)" so that the 'then' in 'run' would not produce an NPE.

[danrubel, 2014/02/26 14:33:47]

I wrapped the call to start in a future so that there won't be any NPE.

+   */
+  Future<AnalysisManager> start() {
     var parser = new ArgParser();
     parser.addFlag(HELP_OPTION,
-        help: "print this help message without starting analysis",
+        help: 'print this help message without starting analysis',
         defaultsTo: false,
         negatable: false);
     parser.addOption(
         SERVER_OPTION,
-        help: "[serverUrl] use an analysis server thats already running");
+        help: '[serverUrl] use an analysis server thats already running');
 
     // Parse arguments
     ArgResults results;
     try {
       results = parser.parse(args);
     } on FormatException catch(e) {
       print(e.message);
       print('');
       printUsage(parser);
       exitCode = 1;
-      return;
+      return null;
     }
     if (results[HELP_OPTION]) {
       printUsage(parser);
-      return;
+      return null;
     }
     if (results.rest.length == 0) {
       printUsage(parser);
       exitCode = 1;
-      return;
+      return null;
     }
     Directory appDir = new Directory(results.rest[0]);
     if (!appDir.existsSync()) {
       print('Specified application directory does not exist: $appDir');
       print('');
       printUsage(parser);
       exitCode = 1;
-      return;
+      return null;
     }
     if (results.rest.length > 1) {
       print('Unexpected arguments after $appDir');
       print('');
       printUsage(parser);
       exitCode = 1;
-      return;
+      return null;
     }
 
-    Future<AnalysisManager> future;
+    // Connect to an already running analysis server
     String serverUrl = results[SERVER_OPTION];
     if (serverUrl != null) {
-      // Connect to an already running analysis server
-      future = AnalysisManager.connect(serverUrl);
+      return AnalysisManager.connect(serverUrl);
+    }
 
-    } else {
-      // Launch and connect to a new analysis server
-      // Assume that the analysis server entry point is in the same directory
-      StringBuffer path = new StringBuffer();
-      path.write(FileSystemEntity.parentOf(Platform.script.toFilePath()));
-      path.write(Platform.pathSeparator);
-      path.write("server.dart");
-      future = AnalysisManager.start(path.toString());
-    }
-    future.then(analyze);
-  }
-
-  void analyze(AnalysisManager mgr) {
-    print("Analyzing...");
-    new Timer(new Duration(seconds: 5), () {
-      if (mgr.stop()) {
-        print("stopped");
-      } else {
-        print("already stopped");
-      }
-    });
+    // Launch and connect to a new analysis server
+    // Assume that the analysis server entry point is in the same directory
+    StringBuffer path = new StringBuffer();
+    path.write(FileSystemEntity.parentOf(Platform.script.toFilePath()));
+    path.write(Platform.pathSeparator);
+    path.write('server.dart');
+    return AnalysisManager.start(path.toString());
   }
 
   /**
+   * Use the given manager to perform the analysis.
+   */
+  void analyze(AnalysisManager manager) {
+    if (manager == null) {
+      return;
+    }
+    this.manager = manager;
+    print('Analyzing...');
+  }
+
+  /**
+   * Stop the analysis server.
+   */
+  void stop() {
+    if (manager != null) {
+      manager.stop();
+    }
+  }
+
+  /**
    * Print information about how to use the server.
    */
   void printUsage(ArgParser parser) {
     print('Usage: $BINARY_NAME [flags] <application_directory>');
     print('');
     print('Supported flags are:');
     print(parser.getUsage());
   }
 }