Calculation of branch configuration will fail if master and develop is equal and is integrated in a feature branch.

[orjan]

I'm having an issue where the BranchConfigurationCalculator will throw when develop is merged to a long running feature without any commits in the feature and within the develop branch.

This line of code will throw since both develop and master is pointing at the same commit.
https://github.com/GitTools/GitVersion/blame/master/src/GitVersionCore/BranchConfigurationCalculator.cs#L53

I've tried to reproduce the issue within a test case but I'm not sure about the final assert?
I've also added some comments that if presents will make GV work.

I think this is releated to #453 but for feature branches.

    [Test]
    public void ShouldBePossibleToMergeDevelopForALongRunningBranch()
    {
        using (var fixture = new EmptyRepositoryFixture(new Config() { VersioningMode = VersioningMode.ContinuousDeployment }))
        {
            fixture.Repository.MakeATaggedCommit("v1.0.0");

            fixture.Repository.CreateBranch("develop");
            fixture.Repository.Checkout("develop");

            fixture.Repository.CreateBranch("feature/longrunning");
            fixture.Repository.Checkout("feature/longrunning");
            fixture.Repository.MakeACommit();

            fixture.Repository.Checkout("develop");
            fixture.Repository.MakeACommit();

            fixture.Repository.Checkout("master");
            fixture.Repository.Merge(fixture.Repository.FindBranch("develop"), SignatureBuilder.SignatureNow());
            fixture.Repository.ApplyTag("v1.1.0");

            /* NOTE: Adding a commit to develop and the version finder will not throw
            {
                fixture.Repository.Checkout("develop");
                fixture.MakeACommit();
                fixture.AssertFullSemver("1.2.0-unstable.1");
            }
            */

            fixture.Repository.Checkout("feature/longrunning"); 
            fixture.Repository.Merge(fixture.Repository.FindBranch("develop"), SignatureBuilder.SignatureNow());

            /* NOTE: adding a commit to the feature and the version finder will not throw, this is our workaround after
             * develop has been integrated into a longrunning branch.
            {
                fixture.Repository.MakeACommit();                
            }
            */

            /*
                First of all im not sure about the assertion here, but it will throw before...
            */
            fixture.AssertFullSemver("1.2.0-longrunning.2");
        }
    }

[JakeGinnivan]

Will be fixed in 3.1

Thanks for taking time and submitting a PR, makes it much easier to diagnose/fix.