Make pub handle missing git more gracefully.

utils/pub/io.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 to make working with IO easier.
  */
 #library('pub_io');
 
 #import('dart:io');
 
 /** Gets the current working directory. */
 String get workingDir() => new File('.').fullPathSync();
 
 /**
+ * Prints the given string to `stderr` on its own line.
+ */
+void printError(value) {
+  stderr.writeString(value.toString());
+  stderr.writeString('\n');
+}
+
+/**
  * Joins a number of path string parts into a single path. Handles
  * platform-specific path separators. Parts can be [String], [Directory], or
  * [File] objects.
  */
 String join(part1, [part2, part3, part4]) {
   final parts = _getPath(part1).split('/');
 
   for (final part in [part2, part3, part4]) {
     if (part == null) continue;
 
@@ skipping 286 matching lines @@
     exitCode = actualExitCode;
     checkComplete();
   };
 
   process.onError = (error) => completer.completeException(error);
 
   return completer.future;
 }
 
 /**
+ * Tests whether or not the git command-line app is available for use.
+ */
+Future<bool> get isGitInstalled() {
+  // TODO(rnystrom): We could cache this after the first check. We aren't right
+  // now because Future.immediate() will invoke its callback synchronously.
+  // That does bad things in cases where the caller expects futures to always
+  // be async. In particular, withGit() in the pub tests which calls
+  // expectAsync() will fail horribly if the test isn't actually async.
+
+  var completer = new Completer<bool>();
+
+  // If "git --version" prints something familiar, git is working.
+  var future = runProcess("git", ["--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;
+}
+
+/**
  * Contains the results of invoking a [Process] and waiting for it to complete.
  */
 class PubProcessResult {
   final List<String> stdout;
   final List<String> stderr;
   final int exitCode;
 
   const PubProcessResult(this.stdout, this.stderr, this.exitCode);
 
   bool get success() => exitCode == 0;
@@ skipping 12 matching lines @@
 }
 
 /**
  * Gets a [Directory] for [entry], which can either already be one, or be a
  * [String].
  */
 Directory _getDirectory(entry) {
   if (entry is Directory) return entry;
   return new Directory(entry);
 }