feat(attr): add bindings and api

lib/src/bindings/attr.dart

@@ -0,0 +1,44 @@
+import 'dart:ffi';
+import 'package:ffi/ffi.dart';
+import '../error.dart';
+import '../util.dart';
+import 'libgit2_bindings.dart';
+
+/// Look up the value of one git attribute for path.
+///
+/// Returned value can be either `true`, `false`, `null` (if the attribute was not set at all),
+/// or a [String] value, if the attribute was set to an actual string.
+///
+/// Throws a [LibGit2Error] if error occured.
+dynamic getAttribute({
+  required Pointer<git_repository> repoPointer,
+  required int flags,
+  required String path,
+  required String name,
+}) {
+  final out = calloc<Pointer<Int8>>();
+  final pathC = path.toNativeUtf8().cast<Int8>();
+  final nameC = name.toNativeUtf8().cast<Int8>();
+  final error = libgit2.git_attr_get(out, repoPointer, flags, pathC, nameC);
+
+  calloc.free(pathC);
+  calloc.free(nameC);
+
+  if (error < 0) {
+    throw LibGit2Error(libgit2.git_error_last());
+  }
+
+  final attributeValue = libgit2.git_attr_value(out.value);
+
+  if (attributeValue == git_attr_value_t.GIT_ATTR_VALUE_UNSPECIFIED) {
+    return null;
+  } else if (attributeValue == git_attr_value_t.GIT_ATTR_VALUE_TRUE) {
+    return true;
+  } else if (attributeValue == git_attr_value_t.GIT_ATTR_VALUE_FALSE) {
+    return false;
+  } else if (attributeValue == git_attr_value_t.GIT_ATTR_VALUE_STRING) {
+    return out.value.cast<Utf8>().toDartString();
+  } else {
+    throw Exception('The attribute value from libgit2 is invalid');
+  }
+}

lib/src/git_types.dart

@@ -1356,3 +1356,31 @@ class GitFeature {
   @override
   String toString() => 'GitFeature.$_name';
 }
+
+/// Combinations of these values determine the lookup order for attribute.
+class GitAttributeCheck {
+  const GitAttributeCheck._(this._value, this._name);
+  final int _value;
+  final String _name;
+
+  static const fileThenIndex = GitAttributeCheck._(0, 'fileThenIndex');
+  static const indexThenFile = GitAttributeCheck._(1, 'indexThenFile');
+  static const indexOnly = GitAttributeCheck._(2, 'indexOnly');
+  static const noSystem = GitAttributeCheck._(4, 'noSystem');
+  static const includeHead = GitAttributeCheck._(8, 'includeHead');
+  static const includeCommit = GitAttributeCheck._(16, 'includeCommit');
+
+  static const List<GitAttributeCheck> values = [
+    fileThenIndex,
+    indexThenFile,
+    indexOnly,
+    noSystem,
+    includeHead,
+    includeCommit,
+  ];
+
+  int get value => _value;
+
+  @override
+  String toString() => 'GitAttributeCheck.$_name';
+}

lib/src/repository.dart

@@ -11,6 +11,7 @@ import 'bindings/checkout.dart' as checkout_bindings;
 import 'bindings/reset.dart' as reset_bindings;
 import 'bindings/diff.dart' as diff_bindings;
 import 'bindings/stash.dart' as stash_bindings;
+import 'bindings/attr.dart' as attr_bindings;
 import 'branch.dart';
 import 'commit.dart';
 import 'config.dart';
@@ -955,4 +956,26 @@ class Repository {
 
   /// Returns [Remotes] object.
   Remotes get remotes => Remotes(this);
+
+  /// Looks up the value of one git attribute for path.
+  ///
+  /// Returned value can be either `true`, `false`, `null` (if the attribute was not set at all),
+  /// or a [String] value, if the attribute was set to an actual string.
+  ///
+  /// Throws a [LibGit2Error] if error occured.
+  dynamic getAttribute({
+    required String path,
+    required String name,
+    Set<GitAttributeCheck> flags = const {GitAttributeCheck.fileThenIndex},
+  }) {
+    final int flagsInt =
+        flags.fold(0, (previousValue, e) => previousValue | e.value);
+
+    return attr_bindings.getAttribute(
+      repoPointer: _repoPointer,
+      flags: flagsInt,
+      path: path,
+      name: name,
+    );
+  }
 }