Convert git wrapper classes to readonly structs

Replaces several internal classes with readonly structs to improve performance by avoiding unnecessary heap allocations. Updates related code to ensure compatibility with the new struct-based implementation.

Author: arturcic

src/GitVersion.LibGit2Sharp/Git/Branch.cs

@@ -3,7 +3,7 @@
 
 namespace GitVersion.Git;
 
-internal sealed class Branch : IBranch
+internal readonly struct Branch : IBranch
 {
     private static readonly LambdaEqualityHelper<IBranch> equalityHelper = new(x => x.Name.Canonical);
     private static readonly LambdaKeyComparer<IBranch, string> comparerHelper = new(x => x.Name.Canonical);

src/GitVersion.LibGit2Sharp/Git/Commit.cs

@@ -4,7 +4,7 @@
 
 namespace GitVersion.Git;
 
-internal sealed class Commit : ICommit
+internal readonly struct Commit : ICommit
 {
     private static readonly ConcurrentDictionary<string, IReadOnlyList<string>> pathsCache = new();
     private static readonly LambdaEqualityHelper<ICommit> equalityHelper = new(x => x.Id);
@@ -19,7 +19,7 @@ internal Commit(LibGit2Sharp.Commit innerCommit, LibGit2Sharp.Diff repoDiff, Git
         repoDiff.NotNull();
         repo.NotNull();
         this.innerCommit = innerCommit.NotNull();
-        this.parentsLazy = new(() => innerCommit.Parents.Select(parent => repo.GetOrWrap(parent, repoDiff)).ToList());
+        this.parentsLazy = new(() => [.. innerCommit.Parents.Select(parent => repo.GetOrWrap(parent, repoDiff))]);
         Id = new ObjectId(innerCommit.Id);
         Sha = innerCommit.Sha;
         When = innerCommit.Committer.When;

src/GitVersion.LibGit2Sharp/Git/ObjectId.cs

@@ -3,7 +3,7 @@
 
 namespace GitVersion.Git;
 
-internal sealed class ObjectId : IObjectId
+internal readonly struct ObjectId : IObjectId
 {
     private static readonly LambdaEqualityHelper<IObjectId> equalityHelper = new(x => x.Sha);
     private static readonly LambdaKeyComparer<IObjectId, string> comparerHelper = new(x => x.Sha);

src/GitVersion.LibGit2Sharp/Git/RefSpec.cs

@@ -3,7 +3,7 @@
 
 namespace GitVersion.Git;
 
-internal class RefSpec : IRefSpec
+internal readonly struct RefSpec : IRefSpec
 {
     private static readonly LambdaEqualityHelper<IRefSpec> equalityHelper = new(x => x.Specification);
     private static readonly LambdaKeyComparer<IRefSpec, string> comparerHelper = new(x => x.Specification);

src/GitVersion.LibGit2Sharp/Git/Reference.cs

@@ -2,32 +2,31 @@
 using GitVersion.Helpers;
 using LibGit2Sharp;
 
-namespace GitVersion.Git
-{
-    internal sealed class Reference : IReference
-    {
-        private static readonly LambdaEqualityHelper<IReference> equalityHelper = new(x => x.Name.Canonical);
-        private static readonly LambdaKeyComparer<IReference, string> comparerHelper = new(x => x.Name.Canonical);
-        internal readonly LibGit2Sharp.Reference innerReference;
+namespace GitVersion.Git;
 
-        internal Reference(LibGit2Sharp.Reference reference)
-        {
-            this.innerReference = reference.NotNull();
-            Name = new ReferenceName(reference.CanonicalName);
+internal readonly struct Reference : IReference
+{
+    private static readonly LambdaEqualityHelper<IReference> equalityHelper = new(x => x.Name.Canonical);
+    private static readonly LambdaKeyComparer<IReference, string> comparerHelper = new(x => x.Name.Canonical);
+    internal readonly LibGit2Sharp.Reference innerReference;
 
-            if (reference is DirectReference)
-                ReferenceTargetId = new ObjectId(reference.TargetIdentifier);
-        }
+    internal Reference(LibGit2Sharp.Reference reference)
+    {
+        this.innerReference = reference.NotNull();
+        Name = new ReferenceName(reference.CanonicalName);
 
-        public ReferenceName Name { get; }
-        public IObjectId? ReferenceTargetId { get; }
-        public int CompareTo(IReference? other) => comparerHelper.Compare(this, other);
-        public override bool Equals(object? obj) => Equals(obj as IReference);
-        public bool Equals(IReference? other) => equalityHelper.Equals(this, other);
-        public override int GetHashCode() => equalityHelper.GetHashCode(this);
-        public override string ToString() => Name.ToString();
-        public string TargetIdentifier => this.innerReference.TargetIdentifier;
-        public static implicit operator LibGit2Sharp.Reference(Reference d)
-            => d.NotNull().innerReference;
+        if (reference is DirectReference)
+            ReferenceTargetId = new ObjectId(reference.TargetIdentifier);
     }
+
+    public ReferenceName Name { get; }
+    public IObjectId? ReferenceTargetId { get; }
+    public int CompareTo(IReference? other) => comparerHelper.Compare(this, other);
+    public override bool Equals(object? obj) => Equals(obj as IReference);
+    public bool Equals(IReference? other) => equalityHelper.Equals(this, other);
+    public override int GetHashCode() => equalityHelper.GetHashCode(this);
+    public override string ToString() => Name.ToString();
+    public string TargetIdentifier => this.innerReference.TargetIdentifier;
+    public static implicit operator LibGit2Sharp.Reference(Reference d)
+        => d.innerReference;
 }

src/GitVersion.LibGit2Sharp/Git/ReferenceCollection.cs

@@ -38,5 +38,5 @@ public IReference? this[string name]
 
     public IReference? Head => this["HEAD"];
 
-    public IEnumerable<IReference> FromGlob(string prefix) => this.innerCollection.FromGlob(prefix).Select(reference => new Reference(reference));
+    public IEnumerable<IReference> FromGlob(string prefix) => this.innerCollection.FromGlob(prefix).Select(reference => (IReference)new Reference(reference));
 }

src/GitVersion.LibGit2Sharp/Git/Remote.cs

@@ -3,7 +3,7 @@
 
 namespace GitVersion.Git;
 
-internal sealed class Remote : IRemote
+internal readonly struct Remote : IRemote
 {
     private static readonly LambdaEqualityHelper<IRemote> equalityHelper = new(x => x.Name);
     private static readonly LambdaKeyComparer<IRemote, string> comparerHelper = new(x => x.Name);

src/GitVersion.LibGit2Sharp/Git/Tag.cs

@@ -4,7 +4,7 @@
 
 namespace GitVersion.Git;
 
-internal sealed class Tag : ITag
+internal readonly struct Tag : ITag
 {
     private static readonly LambdaEqualityHelper<ITag> equalityHelper = new(x => x.Name.Canonical);
     private static readonly LambdaKeyComparer<ITag, string> comparerHelper = new(x => x.Name.Canonical);
@@ -16,9 +16,9 @@ internal sealed class Tag : ITag
     internal Tag(LibGit2Sharp.Tag tag, Diff diff, GitRepository repo)
     {
         this.innerTag = tag.NotNull();
-        this.commitLazy = new(PeeledTargetCommit);
         this.diff = diff.NotNull();
         this.repo = repo.NotNull();
+        this.commitLazy = new(PeeledTargetCommit);
         Name = new(this.innerTag.CanonicalName);
     }
 
@@ -28,7 +28,7 @@ internal Tag(LibGit2Sharp.Tag tag, Diff diff, GitRepository repo)
     public string TargetSha => this.innerTag.Target.Sha;
     public ICommit Commit => this.commitLazy.Value.NotNull();
 
-    private Commit? PeeledTargetCommit()
+    private ICommit? PeeledTargetCommit()
     {
         var target = this.innerTag.Target;
 

src/GitVersion.LibGit2Sharp/Git/TreeChanges.cs

@@ -1,6 +1,6 @@
 namespace GitVersion.Git;
 
-internal sealed class TreeChanges(LibGit2Sharp.TreeChanges innerTreeChanges) : ITreeChanges
+internal readonly struct TreeChanges(LibGit2Sharp.TreeChanges innerTreeChanges) : ITreeChanges
 {
     private readonly LibGit2Sharp.TreeChanges innerTreeChanges = innerTreeChanges ?? throw new ArgumentNullException(nameof(innerTreeChanges));