Various fixes for GH-2967

Author: asbjornu

src/GitVersion.Core/Configuration/ConfigExtensions.cs

@@ -9,7 +9,16 @@ public static class ConfigExtensions
 {
     public static BranchConfig? GetConfigForBranch(this Config config, string? branchName)
     {
-        if (branchName == null) throw new ArgumentNullException(nameof(branchName));
+        if (branchName == null)
+        {
+            throw new ArgumentNullException(nameof(branchName));
+        }
+
+        if (config?.Branches is null)
+        {
+            return null;
+        }
+
         var matches = config.Branches
             .Where(b => Regex.IsMatch(branchName, b.Value?.Regex, RegexOptions.IgnoreCase))
             .ToArray();

src/GitVersion.Core/Core/RepositoryStore.cs

@@ -137,8 +137,14 @@ public ICommit GetBaseVersionSource(ICommit currentBranchTip)
             throw new GitVersionException($"Cannot find commit {currentBranchTip}. Please ensure that the repository is an unshallow clone with `git fetch --unshallow`.", exception);
         }
     }
+
     public IEnumerable<ICommit> GetMainlineCommitLog(ICommit? baseVersionSource, ICommit? mainlineTip)
     {
+        if (mainlineTip is null)
+        {
+            return Enumerable.Empty<ICommit>();
+        }
+
         var filter = new CommitFilter
         {
             IncludeReachableFrom = mainlineTip,
@@ -149,6 +155,7 @@ public IEnumerable<ICommit> GetMainlineCommitLog(ICommit? baseVersionSource, ICo
 
         return this.repository.Commits.QueryBy(filter);
     }
+
     public IEnumerable<ICommit> GetMergeBaseCommits(ICommit? mergeCommit, ICommit? mergedHead, ICommit? findMergeBase)
     {
         var filter = new CommitFilter
@@ -289,20 +296,20 @@ static IEnumerable<IBranch> InnerGetBranchesContainingCommit(ICommit commit, IEn
     public Dictionary<string, List<IBranch>> GetMainlineBranches(ICommit commit, IEnumerable<KeyValuePair<string, BranchConfig?>>? mainlineBranchConfigs) =>
         this.repository.Branches
             .Where(b => mainlineBranchConfigs?.Any(c => c.Value?.Regex != null && Regex.IsMatch(b.Name.Friendly, c.Value.Regex)) == true)
-            .Select(b => new
-            {
-                MergeBase = FindMergeBase(b.Tip!, commit),
-                Branch = b
-            })
-            .Where(a => a.MergeBase != null)
-            .GroupBy(b => b.MergeBase!.Sha, b => b.Branch)
+            .Select(b => new { Origin = FindBranchOrigin(b, commit), Branch = b })
+            .Where(a => a.Origin != null)
+            .GroupBy(b => b.Origin?.Sha, b => b.Branch)
             .ToDictionary(b => b.Key, b => b.ToList());
 
+    private ICommit FindBranchOrigin(IBranch branch, ICommit commit) =>
+        FindMergeBase(branch.Tip!, commit) ?? FindCommitBranchWasBranchedFrom(branch, null).Commit;
+
+
     /// <summary>
     /// Find the commit where the given branch was branched from another branch.
     /// If there are multiple such commits and branches, tries to guess based on commit histories.
     /// </summary>
-    public BranchCommit FindCommitBranchWasBranchedFrom(IBranch branch, Config configuration, params IBranch[] excludedBranches)
+    public BranchCommit FindCommitBranchWasBranchedFrom(IBranch branch, Config? configuration, params IBranch[] excludedBranches)
     {
         if (branch == null)
         {
@@ -456,6 +463,7 @@ private IEnumerable<BranchCommit> GetMergeCommitsForBranch(IBranch branch, Confi
                 return findMergeBase == null ? BranchCommit.Empty : new BranchCommit(findMergeBase, otherBranch);
 
             })
+            .Where(b => b.Commit is not null)
             .OrderByDescending(b => b.Commit.When)
             .ToList();
         this.mergeBaseCommitsCache.Add(branch, branchMergeBases);

src/GitVersion.Core/VersionCalculation/MainlineVersionCalculator.cs

@@ -126,13 +126,28 @@ private IBranch GetMainline(ICommit? baseVersionSource)
         var mainlineBranchConfigs = context.FullConfiguration?.Branches.Where(b => b.Value?.IsMainline == true).ToList();
         var mainlineBranches = this.repositoryStore.GetMainlineBranches(context.CurrentCommit!, mainlineBranchConfigs);
 
-        var allMainlines = mainlineBranches.Values.SelectMany(branches => branches.Select(b => b.Name.Friendly));
-        this.log.Info("Found possible mainline branches: " + string.Join(", ", allMainlines));
+        if (!mainlineBranches.Any())
+        {
+            throw new WarningException("No mainline branches found!");
+        }
+
+        var mainlineBranchNames = mainlineBranches.Values.SelectMany(branches => branches.Select(b => b.Name.Friendly));
+        this.log.Info("Found possible mainline branches: " + string.Join(", ", mainlineBranchNames));
 
         // Find closest mainline branch
-        var firstMatchingCommit = context.CurrentBranch?.Commits.First(c => mainlineBranches.ContainsKey(c.Sha));
+        var firstMatchingCommit = context.CurrentBranch?.Commits.FirstOrDefault(c => mainlineBranches.ContainsKey(c.Sha));
+        if (firstMatchingCommit is null)
+        {
+            var mainlineBranchList = mainlineBranches.Values.SelectMany(x => x).ToList();
+            return FindMainlineBranch(mainlineBranchList, baseVersionSource, context.CurrentCommit);
+        }
+
         var possibleMainlineBranches = mainlineBranches[firstMatchingCommit!.Sha];
+        return FindMainlineBranch(possibleMainlineBranches, baseVersionSource, firstMatchingCommit);
+    }
 
+    private IBranch FindMainlineBranch(List<IBranch> possibleMainlineBranches, ICommit? baseVersionSource, ICommit? firstMatchingCommit)
+    {
         if (possibleMainlineBranches.Count == 1)
         {
             var mainlineBranch = possibleMainlineBranches[0];
@@ -144,11 +159,14 @@ private IBranch GetMainline(ICommit? baseVersionSource)
         if (possibleMainlineBranches.Any(context.CurrentBranch!.Equals))
         {
             this.log.Info($"Choosing {context.CurrentBranch} as mainline because it is the current branch");
-            return context.CurrentBranch;
+            return context.CurrentBranch!;
         }
 
         // prefer a branch on which the merge base was a direct commit, if there is such a branch
-        var firstMatchingCommitBranch = possibleMainlineBranches.FirstOrDefault(b => this.repositoryStore.IsCommitOnBranch(baseVersionSource, b, firstMatchingCommit));
+        var firstMatchingCommitBranch = firstMatchingCommit != null
+            ? possibleMainlineBranches.FirstOrDefault(b => this.repositoryStore.IsCommitOnBranch(baseVersionSource, b, firstMatchingCommit))
+            : null;
+
         if (firstMatchingCommitBranch != null)
         {
             var message = string.Format(