Add initial update-dependencies script.

This script can be used to automatically update dotnet/cli's
dependencies on other repos like CoreFX, NuGet, etc.

Currently the script supports updating the CoreFX dependencies.

scripts/update-dependencies/PushPRTargets.cs

@@ -0,0 +1,108 @@
+// Copyright (c) .NET Foundation and contributors. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using System;
+using Microsoft.DotNet.Cli.Build.Framework;
+using Octokit;
+
+using static Microsoft.DotNet.Cli.Build.Framework.BuildHelpers;
+
+namespace Microsoft.DotNet.Scripts
+{
+    /// <summary>
+    /// Creates a GitHub Pull Request for the current changes in the repo.
+    /// </summary>
+    public static class PushPRTargets
+    {
+        private const string PullRequestTitle = "Updating dependencies from last known good builds";
+
+        private static readonly Config s_config = Config.Instance;
+
+        [Target(nameof(CommitChanges), nameof(CreatePR))]
+        public static BuildTargetResult PushPR(BuildTargetContext c) => c.Success();
+
+        /// <summary>
+        /// Commits all the current changes in the repo and pushes the commit to a remote
+        /// so a PR can be created for it.
+        /// </summary>
+        [Target]
+        public static BuildTargetResult CommitChanges(BuildTargetContext c)
+        {
+            Cmd("git", "add", ".")
+                .Execute()
+                .EnsureSuccessful();
+
+            string userName = s_config.UserName;
+            string email = s_config.Email;
+
+            Cmd("git", "commit", "-m", PullRequestTitle, "--author", $"{userName} <{email}>")
+                .EnvironmentVariable("GIT_COMMITTER_NAME", userName)
+                .EnvironmentVariable("GIT_COMMITTER_EMAIL", email)
+                .Execute()
+                .EnsureSuccessful();
+
+            string remoteUrl = $"github.com/{s_config.GitHubOriginOwner}/{s_config.GitHubProject}.git";
+            string remoteBranchName = $"UpdateDependencies{DateTime.UtcNow.ToString("yyyyMMddhhmmss")}";
+            string refSpec = $"HEAD:refs/heads/{remoteBranchName}";
+
+            string logMessage = $"git push https://{remoteUrl} {refSpec}";
+            BuildReporter.BeginSection("EXEC", logMessage);
+
+            CommandResult pushResult =
+                Cmd("git", "push", $"https://{userName}:{s_config.Password}@{remoteUrl}", refSpec)
+                    .QuietBuildReporter()  // we don't want secrets showing up in our logs
+                    .CaptureStdErr() // git push will write to StdErr upon success, disable that
+                    .CaptureStdOut()
+                    .Execute();
+
+            var message = logMessage + $" exited with {pushResult.ExitCode}";
+            if (pushResult.ExitCode == 0)
+            {
+                BuildReporter.EndSection("EXEC", message.Green(), success: true);
+            }
+            else
+            {
+                BuildReporter.EndSection("EXEC", message.Red().Bold(), success: false);
+            }
+
+            pushResult.EnsureSuccessful(suppressOutput: true);
+
+            c.SetRemoteBranchName(remoteBranchName);
+
+            return c.Success();
+        }
+
+        /// <summary>
+        /// Creates a GitHub PR for the remote branch created above.
+        /// </summary>
+        [Target]
+        public static BuildTargetResult CreatePR(BuildTargetContext c)
+        {
+            string remoteBranchName = c.GetRemoteBranchName();
+
+            NewPullRequest prInfo = new NewPullRequest(
+                PullRequestTitle,
+                s_config.GitHubOriginOwner + ":" + remoteBranchName,
+                s_config.GitHubUpstreamBranch);
+
+            GitHubClient gitHub = new GitHubClient(new ProductHeaderValue("dotnetDependencyUpdater"));
+
+            gitHub.Credentials = new Credentials(s_config.Password);
+
+            PullRequest createdPR = gitHub.PullRequest.Create(s_config.GitHubUpstreamOwner, s_config.GitHubProject, prInfo).Result;
+            c.Info($"Created Pull Request: {createdPR.HtmlUrl}");
+
+            return c.Success();
+        }
+
+        private static string GetRemoteBranchName(this BuildTargetContext c)
+        {
+            return (string)c.BuildContext["RemoteBranchName"];
+        }
+
+        private static void SetRemoteBranchName(this BuildTargetContext c, string value)
+        {
+            c.BuildContext["RemoteBranchName"] = value;
+        }
+    }
+}