remove DDC --build-root option

pkg/dev_compiler/lib/src/compiler/command.dart

 // Copyright (c) 2016, 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:io';
 import 'package:analyzer/src/generated/source.dart' show Source;
 import 'package:analyzer/src/summary/package_bundle_reader.dart'
     show InSummarySource;
 import 'package:args/args.dart' show ArgParser, ArgResults;
 import 'package:args/command_runner.dart' show UsageException;
 import 'package:path/path.dart' as path;
 
 import '../analyzer/context.dart' show AnalyzerOptions, parseDeclaredVariables;
 import 'compiler.dart' show BuildUnit, CompilerOptions, ModuleCompiler;
 import 'module_builder.dart';
 
 final ArgParser _argParser = () {
   var argParser = new ArgParser(allowTrailingOptions: true)
     ..addFlag('help', abbr: 'h', help: 'Display this message.')
     ..addOption('out',
         abbr: 'o', allowMultiple: true, help: 'Output file (required).')
     ..addOption('module-root',
         help: 'Root module directory.\n'
             'Generated module paths are relative to this root.')
     ..addOption('library-root',
         help: 'Root of source files.\n'
-            'Generated library names are relative to this root.')
-    ..addOption('build-root',
-        help: 'Deprecated in favor of --library-root', hide: true);
+            'Generated library names are relative to this root.');
   addModuleFormatOptions(argParser, allowMultiple: true);
   AnalyzerOptions.addArguments(argParser);
   CompilerOptions.addArguments(argParser);
   return argParser;
 }();
 
 /// Runs a single compile for dartdevc.
 ///
 /// This handles argument parsing, usage, error handling.
 /// See bin/dartdevc.dart for the actual entry point, which includes Bazel
@@ skipping 78 matching lines @@
   } else if (outPaths.length != moduleFormats.length) {
     _usageException('Number of output files (${outPaths.length}) must match '
         'number of module formats (${moduleFormats.length}).');
   }
 
   // TODO(jmesserly): for now the first one is special. This will go away once
   // we've removed the "root" and "module name" variables.
   var firstOutPath = outPaths[0];
 
   var libraryRoot = argResults['library-root'] as String;
-  libraryRoot ??= argResults['build-root'] as String;
   if (libraryRoot != null) {
     libraryRoot = path.absolute(libraryRoot);
   } else {
     libraryRoot = Directory.current.path;
   }
   var moduleRoot = argResults['module-root'] as String;
   String modulePath;
   if (moduleRoot != null) {
     moduleRoot = path.absolute(moduleRoot);
     if (!path.isWithin(moduleRoot, firstOutPath)) {
@@ skipping 67 matching lines @@
     '\n\n${_argParser.usage}';
 
 void _usageException(String message) {
   throw new UsageException(message, _usageMessage);
 }
 
 /// Thrown when the input source code has errors.
 class CompileErrorException implements Exception {
   toString() => '\nPlease fix all errors before compiling (warnings are okay).';
 }