Merge pull request #333 from haefele/fix332

Add support for BuildingTag in VisualStudioTeamServices

Author: AArnott

src/NerdBank.GitVersioning.Tests/BuildIntegrationTests.cs

@@ -450,7 +450,6 @@ public static IEnumerable<object[]> CloudBuildOfBranch(string branchName)
         {
             new object[] { CloudBuild.AppVeyor.SetItem("APPVEYOR_REPO_BRANCH", branchName) },
             new object[] { CloudBuild.VSTS.SetItem("BUILD_SOURCEBRANCH", $"refs/heads/{branchName}") },
-            new object[] { CloudBuild.VSTS.SetItem("BUILD_SOURCEBRANCH", branchName) }, // VSTS building a github repo
             new object[] { CloudBuild.Teamcity.SetItem("BUILD_GIT_BRANCH", $"refs/heads/{branchName}") },
         };
     }

src/NerdBank.GitVersioning/CloudBuildServices/VisualStudioTeamServices.cs

@@ -13,14 +13,16 @@
     /// </remarks>
     internal class VisualStudioTeamServices : ICloudBuild
     {
-        public bool IsPullRequest => false; // VSTS doesn't define this.
+        public bool IsPullRequest => Environment.GetEnvironmentVariable("BUILD_SOURCEBRANCH")?.StartsWith("refs/pull/") ?? false;
 
-        public string BuildingTag => null; // VSTS doesn't define this.
-
-        public string BuildingBranch => CloudBuild.ShouldStartWith(Environment.GetEnvironmentVariable("BUILD_SOURCEBRANCH"), "refs/heads/");
-
-        public string BuildingRef => this.BuildingBranch;
+        public string BuildingTag => Environment.GetEnvironmentVariable("BUILD_SOURCEBRANCH")?.StartsWith("refs/tags/") ?? false 
+            ? Environment.GetEnvironmentVariable("BUILD_SOURCEBRANCH") 
+            : null;
 
+        public string BuildingBranch => Environment.GetEnvironmentVariable("BUILD_SOURCEBRANCH")?.StartsWith("refs/heads/") ?? false 
+            ? Environment.GetEnvironmentVariable("BUILD_SOURCEBRANCH")
+            : null;
+        
         public string GitCommitId => null;
 
         public bool IsApplicable => !string.IsNullOrEmpty(Environment.GetEnvironmentVariable("SYSTEM_TEAMPROJECTID"));