Add --x-perf-report flag to the dartanalyzer command

pkg/analyzer_cli/lib/src/options.dart

 // Copyright (c) 2015, 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.
 
 library analyzer_cli.src.options;
 
 import 'dart:io';
 
 import 'package:analyzer_cli/src/driver.dart';
 import 'package:args/args.dart';
@@ skipping 62 matching lines @@
 
   /// Whether to use machine format for error display
   final bool machineFormat;
 
   /// The path to the package root
   final String packageRootPath;
 
   /// The path to a `.packages` configuration file
   final String packageConfigPath;
 
+  /// The path to a file to write a performance log.
+  /// (Or null if not enabled.)
+  final String perfLog;
+
   /// Batch mode (for unit testing)
   final bool shouldBatch;
 
   /// Whether to show package: warnings
   final bool showPackageWarnings;
 
   /// Whether to show SDK warnings
   final bool showSdkWarnings;
 
   /// The source files to analyze
@@ skipping 17 matching lines @@
         enableStrictCallChecks = args['enable-strict-call-checks'],
         enableSuperMixins = args['supermixin'],
         enableTypeChecks = args['enable_type_checks'],
         hintsAreFatal = args['fatal-hints'],
         ignoreUnrecognizedFlags = args['ignore-unrecognized-flags'],
         lints = args['lints'],
         log = args['log'],
         machineFormat = args['machine'] || args['format'] == 'machine',
         packageConfigPath = args['packages'],
         packageRootPath = args['package-root'],
+        perfLog = args['perf-log'],
         shouldBatch = args['batch'],
         showPackageWarnings =
             args['show-package-warnings'] || args['package-warnings'],
         showSdkWarnings = args['show-sdk-warnings'] || args['warnings'],
         sourceFiles = args.rest,
         warningsAreFatal = args['fatal-warnings'],
         strongMode = args['strong'];
 
   /// Parse [args] into [CommandLineOptions] describing the specified
   /// analyzer options. In case of a format error, calls [printAndFail], which
@@ skipping 99 matching lines @@
       ..addFlag('fatal-hints',
           help: 'Treat hints as fatal.', defaultsTo: false, negatable: false)
       ..addFlag('fatal-warnings',
           help: 'Treat non-type warnings as fatal.',
           defaultsTo: false,
           negatable: false)
       ..addFlag('package-warnings',
           help: 'Show warnings from package: imports.',
           defaultsTo: false,
           negatable: false)
+      ..addOption('perf-log',

[Brian Wilkerson, 2015/12/16 15:08:43]

I think I'd prefer to not have this be visible in the help text. Users won't
generally be able to use this information, so there's no point in advertising
it.

Either way, let's document the fact (in the help text) that the format of the
file is not stable and should not be depended on.

[skybrian, 2015/12/16 18:48:10]

For GWT there are compiler flags that are explicitly experimental and begin with
--X. Maybe do something like that here? So, how about
--x-perf-report=path/to/file.json

(I'm thinking of changing the name since this is more of a report than a log.)

[Brian Wilkerson, 2015/12/16 19:06:45]

That would be fine. I just want it to be obvious to end-users that the format of
the file is not something they should depend on. Even just adding
"(Experimental)" to the description would be useful.

If we have "--x-" options (I like that idea), then they should not show up with
the normal options (but perhaps someday we could display them using a "-v"
flag).

+          help: 'Writes a performance log to the given file.')
       ..addFlag('show-package-warnings',
           help: 'Show warnings from package: imports (deprecated).',
           defaultsTo: false,
           negatable: false)
       ..addFlag('warnings',
           help: 'Show warnings from SDK imports.',
           defaultsTo: false,
           negatable: false)
       ..addFlag('show-sdk-warnings',
           help: 'Show warnings from SDK imports (deprecated).',
@@ skipping 238 matching lines @@
 
   int _getNextFlagIndex(args, i) {
     for (; i < args.length; ++i) {
       if (args[i].startsWith('--')) {
         return i;
       }
     }
     return i;
   }
 }