(#260) Correcing AppVeyor Support for Pull Requests

- As per discussion with @nulltoken, implemented a fix for AppVeyor where if the commit sha is not present of any detected local branches, check out a new branch using the sha as the pointer

Author: Gary Ewan Park

GitVersionCore/BuildServers/AppVeyor.cs

@@ -22,12 +22,10 @@ public override void PerformPreProcessingSteps(string gitDirectory)
         {
             if (string.IsNullOrEmpty(gitDirectory))
             {
-                throw new WarningException("Failed to find .git directory on agent. Please make sure agent checkout mode is enabled for you VCS roots - http://confluence.jetbrains.com/display/TCD8/VCS+Checkout+Mode");
+                throw new WarningException("Failed to find .git directory on agent.");
             }
 
-            var repoBranch = Environment.GetEnvironmentVariable("APPVEYOR_REPO_BRANCH");
-
-            GitHelper.NormalizeGitDirectory(gitDirectory, authentication, repoBranch);
+            GitHelper.NormalizeGitDirectory(gitDirectory, authentication);
         }
 
         public override string GenerateSetVersionMessage(string versionToUseForBuildNumber)

GitVersionCore/BuildServers/GitHelper.cs

@@ -9,7 +9,7 @@ public static class GitHelper
     {
         const string MergeMessageRegexPattern = "refs/heads/pull(-requests)?/(?<issuenumber>[0-9]*)/merge";
 
-        public static void NormalizeGitDirectory(string gitDirectory, Authentication authentication, string branch = null)
+        public static void NormalizeGitDirectory(string gitDirectory, Authentication authentication)
         {
             using (var repo = new Repository(gitDirectory))
             {
@@ -25,22 +25,37 @@ public static void NormalizeGitDirectory(string gitDirectory, Authentication aut
 
                 CreateMissingLocalBranchesFromRemoteTrackingOnes(repo, remote.Name);
 
+                var headSha = repo.Refs.Head.TargetIdentifier;
+
                 if (!repo.Info.IsHeadDetached)
                 {
-                    Logger.WriteInfo(string.Format("HEAD points at branch '{0}'.", repo.Refs.Head.TargetIdentifier));
+                    Logger.WriteInfo(string.Format("HEAD points at branch '{0}'.", headSha));
                     return;
                 }
+                
+                Logger.WriteInfo(string.Format("HEAD is detached and points at commit '{0}'.", headSha));
+                
+                // In order to decide whether a fake branch is required or not, first check to see if any local branches have the same commit SHA of the head SHA.
+                // If they do, go ahead and checkout that branch
+                // If no, go ahead and check out a new branch, using the known commit SHA as the pointer
+                var localBranchesWhereCommitShaIsHead = repo.Branches.Where(b => b.Tip.Sha == headSha).ToList();
+
+                if (localBranchesWhereCommitShaIsHead.Count > 1)
+                {
+                    var names = string.Join(", ", localBranchesWhereCommitShaIsHead.Select(r => r.CanonicalName));
+                    var message = string.Format("Found more than one local branch pointing at the commit '{0}'. Unable to determine which one to use ({1}).", headSha, names);
+                    throw new WarningException(message);
+                }
 
-                Logger.WriteInfo(string.Format("HEAD is detached and points at commit '{0}'.", repo.Refs.Head.TargetIdentifier));
-
-                if (branch != null)
+                if (localBranchesWhereCommitShaIsHead.Count == 0)
                 {
-                    Logger.WriteInfo(string.Format("Checking out local branch 'refs/heads/{0}'.", branch));
-                    repo.Checkout("refs/heads/" + branch);
+                    Logger.WriteInfo(string.Format("No local branch pointing at the commit '{0}'. Fake branch needs to be created.", headSha));
+                    CreateFakeBranchPointingAtThePullRequestTip(repo, authentication);
                 }
                 else
                 {
-                    CreateFakeBranchPointingAtThePullRequestTip(repo, authentication);
+                    Logger.WriteInfo(string.Format("Checking out local branch 'refs/heads/{0}'.", localBranchesWhereCommitShaIsHead[0].Name));
+                    repo.Branches[localBranchesWhereCommitShaIsHead[0].Name].Checkout();   
                 }
             }
         }