Add HEAD support for 5.x version, without introduction of new configuration properties.

docs/input/docs/reference/requirements.md

@@ -28,11 +28,6 @@ The repository needs to have an existing local `master` or `main` branch.
 For some branch strategies (such as [Git Flow][gitflow]), a local `develop`
 branch needs to exist.
 
-### Switched branch
-
-The repository should be [switched][git-switch] to a named, existing branch
-pointing to the commit being built (i.e. no detached `HEAD`).
-
 ### Configuration
 
 If using a `GitVersion.yml` [configuration][configuration] file, that file

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

@@ -5,7 +5,6 @@
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Options;
 using NUnit.Framework;
-using Shouldly;
 
 namespace GitVersion.Core.Tests.IntegrationTests;
 
@@ -87,15 +86,14 @@ public void GivenARemoteGitRepositoryAheadOfLocalRepositoryThenChangesShouldPull
     }
 
     [Test]
-    public void GivenARemoteGitRepositoryWhenCheckingOutDetachedHeadUsingExistingImplementationThrowsException()
+    public void GivenARemoteGitRepositoryWhenCheckingOutDetachedHeadUsingExistingImplementationHandleDetachedBranch()
     {
         using var fixture = new RemoteRepositoryFixture();
         Commands.Checkout(
             fixture.LocalRepositoryFixture.Repository,
             fixture.LocalRepositoryFixture.Repository.Head.Tip);
 
-        Should.Throw<WarningException>(() => fixture.AssertFullSemver("0.1.0+4", repository: fixture.LocalRepositoryFixture.Repository, onlyTrackedBranches: false),
-            $"It looks like the branch being examined is a detached Head pointing to commit '{fixture.LocalRepositoryFixture.Repository.Head.Tip.Id.ToString(7)}'. Without a proper branch name GitVersion cannot determine the build version.");
+        fixture.AssertFullSemver("0.1.0--no-branch-.1+4", repository: fixture.LocalRepositoryFixture.Repository, onlyTrackedBranches: false);
     }
 
     [Test]

src/GitVersion.Core/Core/Abstractions/IRepositoryStore.cs

@@ -33,7 +33,7 @@ public interface IRepositoryStore
     /// </summary>
     BranchCommit FindCommitBranchWasBranchedFrom(IBranch? branch, Config configuration, params IBranch[] excludedBranches);
 
-    SemanticVersion GetCurrentCommitTaggedVersion(ICommit? commit, string? tagPrefix);
+    SemanticVersion GetCurrentCommitTaggedVersion(ICommit? commit, string? tagPrefix, bool handleDetachedBranch);
     IEnumerable<SemanticVersion> GetVersionTagsOnBranch(IBranch branch, string? tagPrefixRegex);
     IEnumerable<(ITag Tag, SemanticVersion Semver, ICommit Commit)> GetValidVersionTags(string? tagPrefixRegex, DateTimeOffset? olderThan = null);
 

src/GitVersion.Core/Core/GitVersionContextFactory.cs

@@ -33,7 +33,7 @@ public GitVersionContext Create(GitVersionOptions gitVersionOptions)
             currentBranch = branchForCommit ?? currentBranch;
         }
 
-        var currentCommitTaggedVersion = this.repositoryStore.GetCurrentCommitTaggedVersion(currentCommit, configuration.TagPrefix);
+        var currentCommitTaggedVersion = this.repositoryStore.GetCurrentCommitTaggedVersion(currentCommit, configuration.TagPrefix, handleDetachedBranch: currentBranch.IsDetachedHead);
         var numberOfUncommittedChanges = this.repositoryStore.GetNumberOfUncommittedChanges();
 
         return new GitVersionContext(currentBranch, currentCommit, configuration, currentCommitTaggedVersion, numberOfUncommittedChanges);

src/GitVersion.Core/Core/RepositoryStore.cs

@@ -210,9 +210,9 @@ public BranchCommit FindCommitBranchWasBranchedFrom(IBranch? branch, Config conf
         }
     }
 
-    public SemanticVersion GetCurrentCommitTaggedVersion(ICommit? commit, string? tagPrefix)
+    public SemanticVersion GetCurrentCommitTaggedVersion(ICommit? commit, string? tagPrefix, bool handleDetachedBranch)
         => this.repository.Tags
-            .SelectMany(t => GetCurrentCommitSemanticVersions(commit, tagPrefix, t))
+            .SelectMany(t => GetCurrentCommitSemanticVersions(commit, tagPrefix, t, handleDetachedBranch))
             .Max();
 
     public IEnumerable<SemanticVersion> GetVersionTagsOnBranch(IBranch branch, string? tagPrefixRegex)
@@ -281,12 +281,20 @@ public bool IsCommitOnBranch(ICommit? baseVersionSource, IBranch branch, ICommit
     private static bool IsReleaseBranch(INamedReference branch, IEnumerable<KeyValuePair<string, BranchConfig>> releaseBranchConfig)
         => releaseBranchConfig.Any(c => c.Value?.Regex != null && Regex.IsMatch(branch.Name.Friendly, c.Value.Regex));
 
-    private static IEnumerable<SemanticVersion> GetCurrentCommitSemanticVersions(ICommit? commit, string? tagPrefix, ITag tag)
+    private IEnumerable<SemanticVersion> GetCurrentCommitSemanticVersions(ICommit? commit, string? tagPrefix, ITag tag, bool handleDetachedBranch)
     {
+        if (commit == null)
+            return Array.Empty<SemanticVersion>();
+
         var targetCommit = tag.PeeledTargetCommit();
+        if (targetCommit == null)
+            return Array.Empty<SemanticVersion>();
+
+        var commitToCompare = handleDetachedBranch ? FindMergeBase(commit, targetCommit) : commit;
+
         var tagName = tag.Name.Friendly;
 
-        return targetCommit != null && Equals(targetCommit, commit) && SemanticVersion.TryParse(tagName, tagPrefix, out var version)
+        return Equals(targetCommit, commitToCompare) && SemanticVersion.TryParse(tagName, tagPrefix, out var version)
             ? new[] { version }
             : Array.Empty<SemanticVersion>();
     }

src/GitVersion.Core/VersionCalculation/IncrementStrategyFinder.cs

@@ -53,7 +53,7 @@ public VersionField DetermineIncrementedField(GitVersionContext context, BaseVer
             return defaultIncrement;
         }
 
-        return commitMessageIncrement ?? VersionField.None;
+        return commitMessageIncrement.Value;
     }
 
     public VersionField? GetIncrementForCommits(Config configuration, IEnumerable<ICommit> commits)

src/GitVersion.Core/VersionCalculation/NextVersionCalculator.cs

@@ -40,10 +40,6 @@ public NextVersion FindVersion()
         {
             this.log.Info($"Current commit is tagged with version {Context.CurrentCommitTaggedVersion}, " + "version calculation is for metadata only.");
         }
-        else
-        {
-            EnsureHeadIsNotDetached(Context);
-        }
 
         SemanticVersion? taggedSemanticVersion = null;