feat(worktree): add ability to create worktree from provided reference

lib/src/bindings/branch.dart

@@ -158,6 +158,22 @@ bool isHead(Pointer<git_reference> branch) {
   }
 }
 
+/// Determine if any HEAD points to the current branch.
+///
+/// This will iterate over all known linked repositories (usually in the form of worktrees)
+/// and report whether any HEAD is pointing at the current branch.
+///
+/// Throws a [LibGit2Error] if error occured.
+bool isCheckedOut(Pointer<git_reference> branch) {
+  final result = libgit2.git_branch_is_checked_out(branch);
+
+  if (result < 0) {
+    throw LibGit2Error(libgit2.git_error_last());
+  } else {
+    return result == 1 ? true : false;
+  }
+}
+
 /// Get the branch name.
 ///
 /// Given a reference object, this will check that it really is a branch

lib/src/bindings/worktree.dart

@@ -15,14 +15,23 @@ Pointer<git_worktree> create(
   Pointer<git_repository> repo,
   String name,
   String path,
+  Pointer<git_reference>? ref,
 ) {
   final out = calloc<Pointer<git_worktree>>();
   final nameC = name.toNativeUtf8().cast<Int8>();
   final pathC = path.toNativeUtf8().cast<Int8>();
-  final error = libgit2.git_worktree_add(out, repo, nameC, pathC, nullptr);
+  final opts =
+      calloc<git_worktree_add_options>(sizeOf<git_worktree_add_options>());
+  opts.ref.version = 1;
+  opts.ref.lock = 0;
+  if (ref != null) {
+    opts.ref.ref = ref;
+  }
+  final error = libgit2.git_worktree_add(out, repo, nameC, pathC, opts);
 
   calloc.free(nameC);
   calloc.free(pathC);
+  calloc.free(opts);
 
   if (error < 0) {
     throw LibGit2Error(libgit2.git_error_last());

lib/src/branch.dart

@@ -115,11 +115,19 @@ class Branch {
     return Branch(bindings.rename(_branchPointer, newName, force));
   }
 
-  /// Determines if HEAD points to the given branch.
+  /// Checks if HEAD points to the given branch.
   ///
   /// Throws a [LibGit2Error] if error occured.
   bool get isHead => bindings.isHead(_branchPointer);
 
+  /// Checks if any HEAD points to the current branch.
+  ///
+  /// This will iterate over all known linked repositories (usually in the form of worktrees)
+  /// and report whether any HEAD is pointing at the current branch.
+  ///
+  /// Throws a [LibGit2Error] if error occured.
+  bool get isCheckedOut => bindings.isCheckedOut(_branchPointer);
+
   /// Returns the branch name.
   ///
   /// Given a reference object, this will check that it really is a branch

lib/src/reference.dart

@@ -134,12 +134,14 @@ class Reference {
     );
   }
 
-  /// Pointer to memory address for allocated reference object.
   late Pointer<git_reference> _refPointer;
 
   /// Pointer to memory address for allocated repository object.
   late final Pointer<git_repository> _repoPointer;
 
+  /// Pointer to memory address for allocated reference object.
+  Pointer<git_reference> get pointer => _refPointer;
+
   /// Returns the type of the reference.
   ReferenceType get type {
     return bindings.referenceType(_refPointer) == 1

lib/src/worktree.dart

@@ -1,11 +1,16 @@
 import 'dart:ffi';
 import 'bindings/libgit2_bindings.dart';
 import 'bindings/worktree.dart' as bindings;
+import 'reference.dart';
 import 'repository.dart';
 
 class Worktree {
   /// Initializes a new instance of [Worktree] class by creating new worktree
-  /// with provided [Repository] object worktree [name] and [path].
+  /// with provided [Repository] object worktree [name], [path] and optional [ref]
+  /// [Reference] object.
+  ///
+  /// If [ref] is provided, no new branch will be created but specified [ref] will
+  /// be used instead.
   ///
   /// Should be freed with `free()` to release allocated memory.
   ///
@@ -14,8 +19,9 @@ class Worktree {
     required Repository repo,
     required String name,
     required String path,
+    Reference? ref,
   }) {
-    _worktreePointer = bindings.create(repo.pointer, name, path);
+    _worktreePointer = bindings.create(repo.pointer, name, path, ref?.pointer);
   }
 
   /// Initializes a new instance of [Worktree] class by looking up existing worktree