refactor(revparse)!: add ability to get different git objects based on spec (#46)

lib/src/revparse.dart

@@ -1,6 +1,7 @@
 import 'dart:ffi';
 import 'package:libgit2dart/libgit2dart.dart';
 import 'package:libgit2dart/src/bindings/libgit2_bindings.dart';
+import 'package:libgit2dart/src/bindings/object.dart' as object_bindings;
 import 'package:libgit2dart/src/bindings/revparse.dart' as bindings;
 
 class RevParse {
@@ -40,18 +41,35 @@ class RevParse {
   /// See `man gitrevisions`, or https://git-scm.com/docs/git-rev-parse.html#_specifying_revisions
   /// for information on the syntax accepted.
   ///
+  /// Returned object should be explicitly downcasted to one of four of git
+  /// object types.
+  ///
+  /// ```dart
+  /// final commit = RevParse.single(repo: repo, spec: 'HEAD') as Commit;
+  /// final tree = RevParse.single(repo: repo, spec: 'HEAD^{tree}') as Tree;
+  /// final blob = RevParse.single(repo: repo, spec: 'HEAD:file.txt') as Blob;
+  /// final tag = RevParse.single(repo: repo, spec: 'v1.0') as Tag;
+  /// ```
+  ///
   /// **IMPORTANT**: Should be freed to release allocated memory.
   ///
   /// Throws a [LibGit2Error] if error occured.
-  static Commit single({required Repository repo, required String spec}) {
+  static Object single({required Repository repo, required String spec}) {
-    return Commit(
+    final object = bindings.revParseSingle(
-      bindings
-          .revParseSingle(
       repoPointer: repo.pointer,
       spec: spec,
-          )
-          .cast(),
     );
+    final objectType = object_bindings.type(object);
+
+    if (objectType == GitObject.commit.value) {
+      return Commit(object.cast());
+    } else if (objectType == GitObject.tree.value) {
+      return Tree(object.cast());
+    } else if (objectType == GitObject.blob.value) {
+      return Blob(object.cast());
+    } else {
+      return Tag(object.cast());
+    }
   }
 
   /// Parses a revision string for from, to, and intent.

test/revparse_test.dart

@@ -23,19 +23,30 @@ void main() {
   });
 
   group('revParse', () {
-    test('.single() returns commit with different spec strings', () {
+    test('.single() returns correct objects with different spec strings', () {
-      final headCommit = RevParse.single(repo: repo, spec: 'HEAD');
+      final commit = RevParse.single(repo: repo, spec: 'HEAD') as Commit;
-      expect(headCommit.oid.sha, headSHA);
+      expect(commit, isA<Commit>());
+      expect(commit.oid.sha, headSHA);
 
-      final parentCommit = RevParse.single(repo: repo, spec: 'HEAD^');
+      final tree = RevParse.single(repo: repo, spec: 'HEAD^{tree}') as Tree;
-      expect(parentCommit.oid.sha, parentSHA);
+      expect(tree, isA<Tree>());
+      expect(tree.length, isNonZero);
 
-      final initCommit = RevParse.single(repo: repo, spec: '@{-1}');
+      final blob = RevParse.single(
-      expect(initCommit.oid.sha, '5aecfa0fb97eadaac050ccb99f03c3fb65460ad4');
+        repo: repo,
+        spec: 'HEAD:feature_file',
+      ) as Blob;
+      expect(blob, isA<Blob>());
+      expect(blob.content, 'Feature edit\n');
 
-      headCommit.free();
+      final tag = RevParse.single(repo: repo, spec: 'v0.2') as Tag;
-      parentCommit.free();
+      expect(tag, isA<Tag>());
-      initCommit.free();
+      expect(tag.message, 'annotated tag\n');
+
+      commit.free();
+      tree.free();
+      blob.free();
+      tag.free();
     });
 
     test('.single() throws when spec string not found or invalid', () {

test/worktree_test.dart

@@ -55,7 +55,7 @@ void main() {
     });
 
     test('creates worktree at provided path from provided reference', () {
-      final head = RevParse.single(repo: repo, spec: 'HEAD');
+      final head = RevParse.single(repo: repo, spec: 'HEAD') as Commit;
       final worktreeBranch = Branch.create(
         repo: repo,
         name: 'v1',