Improve ExecuteCore.ExecuteInternal to handle cases where HEAD is not pointing at the desired branch

Author: Jericho

src/GitVersionCore/ExecuteCore.cs

@@ -108,7 +108,18 @@ VersionVariables ExecuteInternal(string targetBranch, string commitId, GitPrepar
 
             return gitPreparer.WithRepository(repo =>
             {
-                var gitVersionContext = new GitVersionContext(repo, configuration, commitId: commitId);
+                // By default, we assume HEAD is pointing to the desired branch
+                var currentBranch = repo.Head;
+
+                // There are some edge cases where HEAD is not pointing to the desired branch.
+                // Therefore it's important to verify if 'currentBranch' is indeed the desired branch
+                if (currentBranch.CanonicalName != targetBranch)
+                {
+                    // In the case where HEAD is not the desired branch, try to find the branch with matching name
+                    currentBranch = repo.Branches.SingleOrDefault(b => b.CanonicalName == targetBranch) ?? repo.Head;
+                }
+
+                var gitVersionContext = new GitVersionContext(repo, currentBranch, configuration, commitId: commitId);
                 var semanticVersion = versionFinder.FindVersion(gitVersionContext);
 
                 return VariableProvider.GetVariablesFor(semanticVersion, gitVersionContext.Configuration, gitVersionContext.IsCurrentCommitTagged);