[spike] Automatically detect the PR branch the user is on

src/GitHub.App/Services/GitClient.cs

@@ -20,6 +20,7 @@ public class GitClient : IGitClient
         const string defaultOriginName = "origin";
         static readonly ILogger log = LogManager.ForContext<GitClient>();
         readonly IGitService gitService;
+        readonly IGitHubCredentialProvider credentialProvider;
         readonly PullOptions pullOptions;
         readonly PushOptions pushOptions;
         readonly FetchOptions fetchOptions;
@@ -31,6 +32,7 @@ public GitClient(IGitHubCredentialProvider credentialProvider, IGitService gitSe
             Guard.ArgumentNotNull(gitService, nameof(gitService));
 
             this.gitService = gitService;
+            this.credentialProvider = credentialProvider;
 
             pushOptions = new PushOptions { CredentialsProvider = credentialProvider.HandleCredentials };
             fetchOptions = new FetchOptions { CredentialsProvider = credentialProvider.HandleCredentials };
@@ -168,6 +170,22 @@ public Task Fetch(IRepository repository, string remoteName, params string[] ref
             });
         }
 
+        public Task<IDictionary<string, string>> ListReferences(IRepository repo, string remoteName)
+        {
+            return Task.Run<IDictionary<string, string>>(() =>
+            {
+                var dictionary = new Dictionary<string, string>();
+                var remote = repo.Network.Remotes[remoteName];
+                var refs = repo.Network.ListReferences(remote, credentialProvider.HandleCredentials);
+                foreach (var reference in refs)
+                {
+                    dictionary[reference.CanonicalName] = reference.TargetIdentifier;
+                }
+
+                return dictionary;
+            });
+        }
+
         public Task Checkout(IRepository repository, string branchName)
         {
             Guard.ArgumentNotNull(repository, nameof(repository));

src/GitHub.App/Services/PullRequestService.cs

@@ -62,7 +62,7 @@ public class PullRequestService : IPullRequestService, IStaticReviewFileMap
         readonly IUsageTracker usageTracker;
 
         readonly IDictionary<string, (string commitId, string repoPath)> tempFileMappings;
-   
+
         [ImportingConstructor]
         public PullRequestService(
             IGitClient gitClient,
@@ -738,11 +738,64 @@ public IObservable<Unit> SwitchToBranch(LocalRepositoryModel repository, PullReq
                         repo.Head.FriendlyName,
                         SettingGHfVSPullRequest);
                     var value = await gitClient.GetConfig<string>(repo, configKey);
-                    return Observable.Return(ParseGHfVSConfigKeyValue(value));
+                    var pr = ParseGHfVSConfigKeyValue(value);
+                    if (pr != default((string, int)))
+                    {
+                        return Observable.Return(pr);
+                    }
+
+                    pr = await FindPullRequestForBranchAsync(repo, repo.Head, "origin");
+                    return Observable.Return(pr);
                 }
             });
         }
 
+        async Task<(string owner, int number)> FindPullRequestForBranchAsync(
+            IRepository repo, Branch branch, string upstreamRemoteName = "origin")
+        {
+            if (!branch.IsTracking)
+            {
+                return default((string, int));
+            }
+
+            var remoteReferences = await gitClient.ListReferences(repo, branch.RemoteName);
+            if (!remoteReferences.TryGetValue(branch.UpstreamBranchCanonicalName, out var sha))
+            {
+                return default((string, int));
+            }
+
+            if (branch.RemoteName != upstreamRemoteName)
+            {
+                remoteReferences = await gitClient.ListReferences(repo, upstreamRemoteName);
+            }
+
+            var prs = remoteReferences
+                    .Where(kv => kv.Value == sha)
+                    .Select(kv => FindPullRequestForCanonicalName(kv.Key))
+                    .Where(p => p != -1)
+                    .ToList();
+            if (prs.Count == 0)
+            {
+                return default((string, int));
+            }
+
+            var owner = gitService.GetRemoteUri(repo, upstreamRemoteName).Owner;
+            var number = prs[0];
+
+            return (owner, number);
+        }
+
+        static int FindPullRequestForCanonicalName(string canonicalName)
+        {
+            var match = Regex.Match(canonicalName, "^refs/pull/([0-9]+)/head$");
+            if (match.Success && int.TryParse(match.Groups[1].Value, out var number))
+            {
+                return number;
+            }
+
+            return -1;
+        }
+
         public async Task<string> ExtractToTempFile(
             LocalRepositoryModel repository,
             PullRequestDetailModel pullRequest,

src/GitHub.Exports.Reactive/Services/IGitClient.cs

@@ -56,6 +56,9 @@ public interface IGitClient
         /// <returns></returns>
         Task Fetch(IRepository repository, UriString remoteUri, params string[] refspecs);
 
+        // blar!
+        Task<IDictionary<string, string>> ListReferences(IRepository repo, string remoteName);
+
         /// <summary>
         /// Checks out a branch.
         /// </summary>