feat(repository): add ability to set head

lib/src/repository.dart

@@ -1,5 +1,6 @@
 import 'dart:ffi';
 import 'odb.dart';
+import 'oid.dart';
 import 'reference.dart';
 import 'bindings/libgit2_bindings.dart';
 import 'bindings/repository.dart' as bindings;
@@ -77,11 +78,11 @@ class Repository {
     return bindings.isHeadDetached(_repoPointer);
   }
 
-  /// Makes the repository HEAD point to the specified reference.
+  /// Makes the repository HEAD point to the specified reference or commit.
   ///
-  /// If the provided [reference] points to a Tree or a Blob, the HEAD is unaltered.
+  /// If the provided [target] points to a Tree or a Blob, the HEAD is unaltered.
   ///
-  /// If the provided [reference] points to a branch, the HEAD will point to that branch,
+  /// If the provided [target] points to a branch, the HEAD will point to that branch,
   /// staying attached, or become attached if it isn't yet.
   ///
   /// If the branch doesn't exist yet, the HEAD will be attached to an unborn branch.
@@ -89,8 +90,22 @@ class Repository {
   /// Otherwise, the HEAD will be detached and will directly point to the Commit.
   ///
   /// Throws a [LibGit2Error] if error occured.
-  void setHead(String reference) {
-    bindings.setHead(_repoPointer, reference);
+  void setHead(String target) {
+    late final Oid oid;
+
+    if (isValidShaHex(target)) {
+      if (target.length == 40) {
+        oid = Oid.fromSHA(target);
+      } else {
+        final shortOid = Oid.fromSHAn(target);
+        final odb = this.odb;
+        oid = Oid(odb.existsPrefix(shortOid.pointer, target.length));
+        odb.free();
+      }
+      bindings.setHeadDetached(_repoPointer, oid.pointer);
+    } else {
+      bindings.setHead(_repoPointer, target);
+    }
   }
 
   /// Checks if the current branch is unborn.

test/repository_test.dart

@@ -50,15 +50,6 @@ void main() {
         test('returns empty string as path of the working directory', () {
           expect(repo.workdir, '');
         });
-
-        group('setHead', () {
-          test('throws when reference doesn\'t exist', () {
-            expect(
-              () => repo.setHead('refs/tags/doesnt/exist'),
-              throwsA(isA<LibGit2Error>()),
-            );
-          });
-        });
       });
 
       group('standard', () {
@@ -130,9 +121,12 @@ void main() {
     });
 
     group('testrepo', () {
+      const lastCommit = '78b8bf123e3952c970ae5c1ce0a3ea1d1336f6e8';
+      const featureCommit = '5aecfa0fb97eadaac050ccb99f03c3fb65460ad4';
+
       final tmpDir = '${Directory.systemTemp.path}/testrepo/';
 
-      setUpAll(() async {
+      setUp(() async {
         if (await Directory(tmpDir).exists()) {
           await Directory(tmpDir).delete(recursive: true);
         }
@@ -143,7 +137,7 @@ void main() {
         repo = Repository.open(tmpDir);
       });
 
-      tearDownAll(() async {
+      tearDown(() async {
         repo.free();
         await Directory(tmpDir).delete(recursive: true);
       });
@@ -159,6 +153,37 @@ void main() {
         repo.setNamespace(null);
         expect(repo.namespace, '');
       });
+
+      group('setHead', () {
+        test('successfully sets head when target is reference', () {
+          expect(repo.head.name, 'refs/heads/master');
+          expect(repo.head.target.sha, lastCommit);
+          repo.setHead('refs/heads/feature');
+          expect(repo.head.name, 'refs/heads/feature');
+          expect(repo.head.target.sha, featureCommit);
+        });
+
+        test('successfully sets head when target is sha hex', () {
+          expect(repo.head.target.sha, lastCommit);
+          repo.setHead(featureCommit);
+          expect(repo.head.target.sha, featureCommit);
+          expect(repo.isHeadDetached, true);
+        });
+
+        test('successfully sets head when target is short sha hex', () {
+          expect(repo.head.target.sha, lastCommit);
+          repo.setHead(featureCommit.substring(0, 5));
+          expect(repo.head.target.sha, featureCommit);
+          expect(repo.isHeadDetached, true);
+        });
+
+        test('successfully attaches to an unborn branch', () {
+          expect(repo.head.name, 'refs/heads/master');
+          expect(repo.isBranchUnborn, false);
+          repo.setHead('refs/heads/not.there');
+          expect(repo.isBranchUnborn, true);
+        });
+      });
     });
   });
 }