Include stderr on git failure.

utils/pub/git.dart

Index: utils/pub/git.dart
diff --git a/utils/pub/git.dart b/utils/pub/git.dart
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+++ b/utils/pub/git.dart
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+// 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('git');
+
+#import('io.dart');
+#import('utils.dart');
+
+/// Tests whether or not the git command-line app is available for use.
+Future<bool> get isInstalled {
+  if (_isGitInstalledCache != null) {
+    // TODO(rnystrom): The sleep is to pump the message queue. Can use
+    // Future.immediate() when #3356 is fixed.
+    return sleep(0).transform((_) => _isGitInstalledCache);
+  }
+
+  return _gitCommand.transform((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]) {
+  return _gitCommand.chain((git) {
+    return runProcess(git, args, workingDir);
+  }).transform((result) {
+    if (!result.success) throw new Exception(
+        'Git failed:\n${Strings.join(result.stderr, "\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
+/// found on the user's PATH.
+Future<String> get _gitCommand {
+  // TODO(nweiz): Just use Future.immediate once issue 3356 is fixed.
+  if (_gitCommandCache != null) {
+    return sleep(0).transform((_) => _gitCommandCache);
+  }
+
+  return _tryGitCommand("git").chain((success) {
+    if (success) return new Future.immediate("git");
+
+    // Git is sometimes installed on Windows as `git.cmd`
+    return _tryGitCommand("git.cmd").transform((success) {
+      if (success) return "git.cmd";
+      return null;
+    });
+  }).transform((command) {
+    _gitCommandCache = command;
+    return command;
+  });
+}
+
+/// Checks whether [command] is the Git command for this computer.
+Future<bool> _tryGitCommand(String command) {
+  var completer = new Completer<bool>();
+
+  // If "git --version" prints something familiar, git is working.
+  var future = runProcess(command, ["--version"]);
+
+  future.then((results) {
+    var regex = new RegExp("^git version");
+    completer.complete(results.stdout.length == 1 &&
+                       regex.hasMatch(results.stdout[0]));
+  });
+
+  future.handleException((err) {
+    // If the process failed, they probably don't have it.
+    completer.complete(false);
+    return true;
+  });
+
+  return completer.future;
+}