Compare Mainline branch candidates without remote

- Refactor `GetMainlineBranches` into many smaller methods.
- Add logging in each method.
- Compare Mainline branch candidates without remote.

Author: asbjornu

src/GitVersion.Core.Tests/IntegrationTests/MainlineDevelopmentMode.cs

@@ -562,7 +562,7 @@ public void GivenNoMainThrowsWarning()
         fixture.Repository.Branches.Remove(fixture.Repository.Branches["main"]);
 
         var exception = Assert.Throws<WarningException>(() => fixture.AssertFullSemver("1.1.0-alpha.1", config));
-        exception.Message.ShouldMatch("No branches can be found matching the commit .* in the configured Mainline branches: main, support");
+        exception!.Message.ShouldMatch("No branches can be found matching the commit .* in the configured Mainline branches: main, support");
     }
 }
 

src/GitVersion.Core/Core/RepositoryStore.cs

@@ -295,14 +295,50 @@ 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)
+            .Where(b => BranchIsMainline(b, mainlineBranchConfigs))
             .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());
+            .Where(x => x.Origin is not null)
+            .GroupBy(x => x.Origin!.Sha, a => a.Branch)
+            .ToDictionary(x => x.Key, x => x.ToList());
+
+    private bool BranchIsMainline(INamedReference branch, IEnumerable<KeyValuePair<string, BranchConfig?>>? mainlineBranchConfigs) =>
+        mainlineBranchConfigs?.Any(c => BranchMatchesMainlineConfig(branch, c)) == true;
+
+    private bool BranchMatchesMainlineConfig(INamedReference branch, KeyValuePair<string, BranchConfig?> mainlineBranchConfig)
+    {
+        if (mainlineBranchConfig.Value?.Regex == null)
+        {
+            return false;
+        }
+
+        var mainlineRegex = mainlineBranchConfig.Value.Regex;
+        var branchName = branch.Name.WithoutRemote;
+        var match = Regex.IsMatch(branchName, mainlineRegex);
+        this.log.Info($"'{mainlineRegex}' {(match ? "matches" : "does not match")} '{branchName}'.");
+        return match;
+    }
+
+    private ICommit? FindBranchOrigin(IBranch branch, ICommit commit)
+    {
+        var branchName = branch.Name.Friendly;
+        var mergeBase = FindMergeBase(branch.Tip!, commit);
+        if (mergeBase is not null)
+        {
+            this.log.Info($"Found merge base {mergeBase.Sha} for '{branchName}'.");
+            return mergeBase;
+        }
+
+        var branchCommit = FindCommitBranchWasBranchedFrom(branch, null);
+        if (branchCommit != BranchCommit.Empty)
+        {
+            this.log.Info($"Found parent commit {branchCommit.Commit.Sha} for '{branchName}'.");
+            return branchCommit.Commit;
+        }
+
+        this.log.Info($"Found no merge base or parent commit for '{branchName}'.");
+        return null;
+    }
 
-    private ICommit FindBranchOrigin(IBranch branch, ICommit commit) =>
-        FindMergeBase(branch.Tip!, commit) ?? FindCommitBranchWasBranchedFrom(branch, null).Commit;
 
 
     /// <summary>

src/GitVersion.Core/VersionCalculation/MainlineVersionCalculator.cs

@@ -129,7 +129,7 @@ private IBranch GetMainline(ICommit? baseVersionSource)
         if (!mainlineBranches.Any())
         {
             var mainlineBranchConfigsString = string.Join(", ", mainlineBranchConfigs.Select(b => b.Value.Name));
-            throw new WarningException($"No branches can be found matching the commit {context.CurrentCommit.Sha} in the configured Mainline branches: {mainlineBranchConfigsString}");
+            throw new WarningException($"No branches can be found matching the commit {context.CurrentCommit?.Sha} in the configured Mainline branches: {mainlineBranchConfigsString}");
         }
 
         var mainlineBranchNames = mainlineBranches.Values.SelectMany(branches => branches.Select(b => b.Name.Friendly));