Fix GitVersion calculates the wrong version after main is merged back to develop.

Author: arturcic

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

@@ -1218,4 +1218,57 @@ public void EnsurePreventIncrementWhenCurrentCommitTaggedOnReleaseBranchAndIncre
 
         fixture.AssertFullSemver(semVersion, configuration);
     }
+
+    [TestCase(false, "2.0.0-alpha.3")]
+    [TestCase(true, "2.0.0-alpha.2")]
+    public void EnsureVersionAfterMainIsMergedBackToDevelopIsCorrectForTrunkBased(bool applyTag, string semanticVersion)
+    {
+        var configuration = GitFlowConfigurationBuilder.New
+            .WithVersionStrategy(VersionStrategies.TrunkBased)
+            .Build();
+
+        using var fixture = new EmptyRepositoryFixture("main");
+
+        fixture.MakeACommit("A");
+        fixture.ApplyTag("1.0.0");
+        fixture.BranchTo("develop");
+        fixture.MakeACommit("B +semver: major");
+
+        // ✅ succeeds as expected
+        fixture.AssertFullSemver("2.0.0-alpha.1", configuration);
+
+        fixture.Checkout("main");
+        fixture.MakeACommit("C");
+        if (applyTag) fixture.ApplyTag("1.0.1");
+        fixture.Checkout("develop");
+        fixture.MergeNoFF("main");
+
+        // ✅ succeeds as expected
+        fixture.AssertFullSemver(semanticVersion, configuration);
+    }
+
+    [Test]
+    public void EnsureVersionAfterMainIsMergedBackToDevelopIsCorrectForGitFlow()
+    {
+        var configuration = GitFlowConfigurationBuilder.New.Build();
+
+        using var fixture = new EmptyRepositoryFixture("main");
+
+        fixture.MakeACommit("A");
+        fixture.ApplyTag("1.0.0");
+        fixture.BranchTo("develop");
+        fixture.MakeACommit("B +semver: major");
+
+        // ✅ succeeds as expected
+        fixture.AssertFullSemver("2.0.0-alpha.1", configuration);
+
+        fixture.Checkout("main");
+        fixture.MakeACommit("C");
+        fixture.ApplyTag("1.0.1");
+        fixture.Checkout("develop");
+        fixture.MergeNoFF("main");
+
+        // ✅ succeeds as expected
+        fixture.AssertFullSemver("2.0.0-alpha.3", configuration);
+    }
 }

src/GitVersion.Core/VersionCalculation/IncrementStrategyFinder.cs

@@ -40,7 +40,7 @@ public VersionField DetermineIncrementedField(
         configuration.NotNull();
 
         var commitMessageIncrement = FindCommitMessageIncrement(
-            configuration, baseVersion.BaseVersionSource, currentCommit, label);
+            configuration, baseVersion, currentCommit, label);
 
         var defaultIncrement = configuration.Increment.ToVersionField();
 
@@ -81,31 +81,38 @@ public VersionField DetermineIncrementedField(
     }
 
     private VersionField? FindCommitMessageIncrement(
-        EffectiveConfiguration configuration, ICommit? baseCommit, ICommit? currentCommit, string? label)
+        EffectiveConfiguration configuration, BaseVersion baseVersion, ICommit? currentCommit, string? label)
     {
         if (configuration.CommitMessageIncrementing == CommitMessageIncrementMode.Disabled)
         {
             return null;
         }
 
+        var baseCommit = baseVersion.BaseVersionSource;
+
         //get tags with valid version - depends on configuration (see #3757)
         var targetShas = new Lazy<IReadOnlySet<string>>(() =>
             this.taggedSemanticVersionRepository.GetTaggedSemanticVersions(configuration.TagPrefix, configuration.SemanticVersionFormat)
-            .SelectMany(_ => _).Where(_ => _.Value.IsMatchForBranchSpecificLabel(label)).Select(_ => _.Tag.TargetSha).ToHashSet()
+                .SelectMany(_ => _).Where(_ => _.Value.IsMatchForBranchSpecificLabel(label)).Select(_ => _.Tag.TargetSha).ToHashSet()
         );
 
-        var commits = GetIntermediateCommits(baseCommit, currentCommit);
+        var targetTags = this.taggedSemanticVersionRepository
+            .GetTaggedSemanticVersions(configuration.TagPrefix, configuration.SemanticVersionFormat)
+            .SelectMany(_ => _).Where(element => element.Value.IsMatchForBranchSpecificLabel(label)
+                && element.Value.CompareTo(baseVersion.GetSemanticVersion()) == 0).Select(_ => _.Tag.TargetSha).ToHashSet();
+
+        var intermediateCommits = GetIntermediateCommits(baseCommit, currentCommit);
         // consider commit messages since latest tag only (see #3071)
-        commits = commits
+        var commits = intermediateCommits
             .Reverse()
-            .TakeWhile(x => !targetShas.Value.Contains(x.Sha))
+            .TakeWhile(x => baseCommit != x)
+            .Where(element => !targetShas.Value.Contains(element.Sha))
             .Reverse();
 
         if (configuration.CommitMessageIncrementing == CommitMessageIncrementMode.MergeMessageOnly)
         {
             commits = commits.Where(c => c.Parents.Count() > 1);
         }
-
         return GetIncrementForCommits(
             majorVersionBumpMessage: configuration.MajorVersionBumpMessage,
             minorVersionBumpMessage: configuration.MinorVersionBumpMessage,