feat(merge): add bindings and api for merge analysis

test/merge_test.dart

@@ -0,0 +1,85 @@
+import 'dart:io';
+import 'package:test/test.dart';
+import 'package:libgit2dart/libgit2dart.dart';
+import 'helpers/util.dart';
+
+void main() {
+  late Repository repo;
+  final tmpDir = '${Directory.systemTemp.path}/merge_testrepo/';
+
+  setUp(() async {
+    if (await Directory(tmpDir).exists()) {
+      await Directory(tmpDir).delete(recursive: true);
+    }
+    await copyRepo(
+      from: Directory('test/assets/testrepo/'),
+      to: await Directory(tmpDir).create(),
+    );
+    repo = Repository.open(tmpDir);
+  });
+
+  tearDown(() async {
+    repo.free();
+    await Directory(tmpDir).delete(recursive: true);
+  });
+
+  group('Merge', () {
+    group('analysis', () {
+      test('is up to date when no reference is provided', () {
+        final commit =
+            repo['c68ff54aabf660fcdd9a2838d401583fe31249e3'] as Commit;
+        final result = repo.mergeAnalysis(commit.id);
+
+        expect(result[0], GitMergeAnalysis.upToDate.value);
+        expect(repo.status, isEmpty);
+
+        commit.free();
+      });
+
+      test('is up to date for provided ref', () {
+        final commit =
+            repo['c68ff54aabf660fcdd9a2838d401583fe31249e3'] as Commit;
+        final result = repo.mergeAnalysis(commit.id, 'refs/tags/v0.1');
+
+        expect(result[0], GitMergeAnalysis.upToDate.value);
+        expect(repo.status, isEmpty);
+
+        commit.free();
+      });
+
+      test('is fast forward', () {
+        final theirHead =
+            repo['6cbc22e509d72758ab4c8d9f287ea846b90c448b'] as Commit;
+        final ffCommit =
+            repo['f17d0d48eae3aa08cecf29128a35e310c97b3521'] as Commit;
+        final ffBranch = repo.branches.create(
+          name: 'ff-branch',
+          target: ffCommit,
+        );
+
+        final result = repo.mergeAnalysis(theirHead.id, ffBranch.name);
+
+        expect(
+          result[0],
+          GitMergeAnalysis.fastForward.value + GitMergeAnalysis.normal.value,
+        );
+        expect(repo.status, isEmpty);
+
+        ffBranch.free();
+        ffCommit.free();
+        theirHead.free();
+      });
+
+      test('is not fast forward and there is no conflicts', () {
+        final commit =
+            repo['5aecfa0fb97eadaac050ccb99f03c3fb65460ad4'] as Commit;
+        final result = repo.mergeAnalysis(commit.id);
+
+        expect(result[0], GitMergeAnalysis.normal.value);
+        expect(repo.status, isEmpty);
+
+        commit.free();
+      });
+    });
+  });
+}