Added tag-prefix configuration option

Author: JakeGinnivan

GitVersionCore.Tests/IntegrationTests/GitHubFlow/MasterTests.cs

@@ -136,4 +136,30 @@ public void GivenARepositoryWithTagAndOldNextVersionTxtFileAndNoCommits_VersionS
             fixture.AssertFullSemver("1.1.0+0");
         }
     }
+
+    [Test]
+    public void CanSpecifyTagPrefixes()
+    {
+        using (var fixture = new EmptyRepositoryFixture(new Config{ TagPrefix = "version-"}))
+        {
+            const string TaggedVersion = "version-1.0.3";
+            fixture.Repository.MakeATaggedCommit(TaggedVersion);
+            fixture.Repository.MakeCommits(5);
+
+            fixture.AssertFullSemver("1.0.4+5");
+        }
+    }
+
+    [Test]
+    public void CanSpecifyTagPrefixesAsRegex()
+    {
+        using (var fixture = new EmptyRepositoryFixture(new Config{ TagPrefix = "[version-|v]"}))
+        {
+            const string TaggedVersion = "v1.0.3";
+            fixture.Repository.MakeATaggedCommit(TaggedVersion);
+            fixture.Repository.MakeCommits(5);
+
+            fixture.AssertFullSemver("1.0.4+5");
+        }
+    }
 }

GitVersionCore/Configuration/Config.cs

@@ -9,6 +9,7 @@ public Config()
             AssemblyVersioningScheme = AssemblyVersioningScheme.MajorMinorPatch;
             DevelopBranchTag = "unstable";
             ReleaseBranchTag = "beta";
+            TagPrefix = "v";
         }
 
         public AssemblyVersioningScheme AssemblyVersioningScheme { get; set; }
@@ -18,5 +19,8 @@ public Config()
 
         [YamlAlias("release-branch-tag")]
         public string ReleaseBranchTag { get; set; }
+
+        [YamlAlias("tag-prefix")]
+        public string TagPrefix { get; set; }
     }
 }

GitVersionCore/GitHubFlow/LastTaggedReleaseFinder.cs

@@ -1,6 +1,8 @@
 namespace GitVersion
 {
+    using System;
     using System.Linq;
+    using System.Text.RegularExpressions;
     using LibGit2Sharp;
 
     public class LastTaggedReleaseFinder
@@ -16,8 +18,9 @@ public bool GetVersion(out VersionTaggedCommit versionTaggedCommit)
         {
             var tags = context.Repository.Tags.Select(t =>
             {
+                var match = Regex.Match(t.Name, string.Format("({0})?(?<version>.*)", context.Configuration.TagPrefix));
                 SemanticVersion version;
-                if (SemanticVersion.TryParse(t.Name.TrimStart('v'), out version))
+                if (SemanticVersion.TryParse(match.Groups["version"].Value, out version))
                 {
                     return new VersionTaggedCommit((Commit)t.Target, version);
                 }