Don't fetch git repository unnecessarily when running "pub get".

sdk/lib/_internal/pub/lib/src/git.dart

 // Copyright (c) 2012, 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.
 
 /// Helper functionality for invoking Git.
 library pub.git;
 
 import 'dart:async';
 import 'dart:io';
 
 import 'io.dart';
 import 'log.dart' as log;
 
+/// An exception thrown because a git command failed.
+class GitException implements Exception {

[Bob Nystrom, 2014/04/01 23:43:34]

I think we tend to import this library with a prefix. "git.GitException" seems
weird to me, but then calling it "Exception" is a bit odd too. Thoughts?

[nweiz, 2014/04/02 00:41:19]

I think shadowing core types is worse than having a redundant prefix, although I
sure wish the core library didn't use both Exception *and* Error, since it gives
prefixed libraries nowhere else to go.

+  /// The arguments to the git command.
+  final List<String> args;
+
+  /// The standard error emitted by git.
+  final String stderr;
+
+  String get message => 'Git error. Command: git ${args.join(" ")}\n$stderr';
+
+  GitException(Iterable<String> args, this.stderr)
+      : args = args.toList();
+
+  String toString() => message;
+}
+
 /// Tests whether or not the git command-line app is available for use.
 Future<bool> get isInstalled {
   if (_isGitInstalledCache != null) {
     return new Future.value(_isGitInstalledCache);
   }
 
   return _gitCommand.then((git) => git != null);
 }
 
 /// Run a git process with [args] from [workingDir]. Returns the stdout as a
 /// list of strings if it succeeded. Completes to an exception if it failed.
 Future<List<String>> run(List<String> args,
     {String workingDir, Map<String, String> environment}) {
   return _gitCommand.then((git) {
     return runProcess(git, args, workingDir: workingDir,
         environment: environment);
   }).then((result) {
-    if (!result.success) throw new Exception(
-        'Git error. Command: git ${args.join(" ")}\n'
-        '${result.stderr.join("\n")}');
-
+    if (!result.success) throw new GitException(args, result.stderr.join("\n"));
     return result.stdout;
   });
 }
 
 bool _isGitInstalledCache;
 
 /// The cached Git command.
 String _gitCommandCache;
 
 /// Returns the name of the git command-line app, or null if Git could not be
@@ skipping 27 matching lines @@
   }).catchError((err, stackTrace) {
     // If the process failed, they probably don't have it.
     if (err is ProcessException) {
       log.io('Git command is not "$command": $err\n$stackTrace');
       return false;
     }
 
     throw err;
   });
 }