feat(diff): add binding and API method for git_diff_tree_to_workdir_with_index (#23)

lib/src/bindings/diff.dart

@@ -89,6 +89,44 @@ Pointer<git_diff> treeToWorkdir({
   return out.value;
 }
 
+/// Create a diff between a tree and the working directory using index data to
+/// account for staged deletes, tracked files, etc.
+///
+/// This emulates `git diff <tree>` by diffing the tree to the index and the
+/// index to the working directory and blending the results into a single diff
+/// that includes staged deleted, etc.
+///
+/// Throws a [LibGit2Error] if error occured.
+Pointer<git_diff> treeToWorkdirWithIndex({
+  required Pointer<git_repository> repoPointer,
+  required Pointer<git_tree>? treePointer,
+  required int flags,
+  required int contextLines,
+  required int interhunkLines,
+}) {
+  final out = calloc<Pointer<git_diff>>();
+  final opts = _diffOptionsInit(
+    flags: flags,
+    contextLines: contextLines,
+    interhunkLines: interhunkLines,
+  );
+
+  final error = libgit2.git_diff_tree_to_workdir_with_index(
+    out,
+    repoPointer,
+    treePointer ?? nullptr,
+    opts,
+  );
+
+  if (error < 0) {
+    throw LibGit2Error(libgit2.git_error_last());
+  }
+
+  calloc.free(opts);
+
+  return out.value;
+}
+
 /// Create a diff with the difference between two tree objects.
 ///
 /// Throws a [LibGit2Error] if error occured.

lib/src/diff.dart

@@ -14,6 +14,44 @@ class Diff {
   /// **IMPORTANT**: Should be freed to release allocated memory.
   Diff(this._diffPointer);
 
+  /// Creates a diff between a [tree] and the working directory using index
+  /// data to account for staged deletes, tracked files, etc.
+  ///
+  /// This emulates `git diff <tree>` by diffing the tree to the index and the
+  /// index to the working directory and blending the results into a single diff
+  /// that includes staged deleted, etc.
+  ///
+  /// [repo] is the repository containing the tree.
+  ///
+  /// [tree] is a [Tree] object to diff from, or null for empty tree.
+  ///
+  /// [flags] is a combination of [GitDiff] flags. Defaults to [GitDiff.normal].
+  ///
+  /// [contextLines] is the number of unchanged lines that define the boundary
+  /// of a hunk (and to display before and after). Defaults to 3.
+  ///
+  /// [interhunkLines] is the maximum number of unchanged lines between hunk
+  /// boundaries before the hunks will be merged into one. Defaults to 0.
+  ///
+  /// **IMPORTANT**: Should be freed to release allocated memory.
+  ///
+  /// Throws a [LibGit2Error] if error occured.
+  Diff.treeToWorkdirWithIndex({
+    required Repository repo,
+    required Tree? tree,
+    Set<GitDiff> flags = const {GitDiff.normal},
+    int contextLines = 3,
+    int interhunkLines = 0,
+  }) {
+    _diffPointer = bindings.treeToWorkdirWithIndex(
+      repoPointer: repo.pointer,
+      treePointer: tree?.pointer,
+      flags: flags.fold(0, (acc, e) => acc | e.value),
+      contextLines: contextLines,
+      interhunkLines: interhunkLines,
+    );
+  }
+
   /// Reads the [content]s of a git patch file into a git diff object.
   ///
   /// The diff object produced is similar to the one that would be produced if

test/diff_test.dart

@@ -56,6 +56,20 @@ void main() {
     'subdir/modified_file',
   ];
 
+  const treeToWorkdirWithIndex = [
+    'file_deleted',
+    'modified_file',
+    'staged_changes',
+    'staged_changes_file_deleted',
+    'staged_changes_file_modified',
+    'staged_delete',
+    'staged_delete_file_modified',
+    'staged_new',
+    'staged_new_file_modified',
+    'subdir/deleted_file',
+    'subdir/modified_file',
+  ];
+
   const patchText = """
 diff --git a/subdir/modified_file b/subdir/modified_file
 index e69de29..c217c63 100644
@@ -205,6 +219,23 @@ index e69de29..c217c63 100644
       tree.free();
     });
 
+    test('returns diff between tree and workdir with index', () {
+      final head = repo.head;
+      final commit = repo.lookupCommit(head.target);
+      final tree = commit.tree;
+
+      final diff = Diff.treeToWorkdirWithIndex(repo: repo, tree: tree);
+      expect(diff.length, 11);
+      for (var i = 0; i < diff.deltas.length; i++) {
+        expect(diff.deltas[i].newFile.path, treeToWorkdirWithIndex[i]);
+      }
+
+      diff.free();
+      tree.free();
+      commit.free();
+      head.free();
+    });
+
     test('successfully merges diffs', () {
       final head = repo.head;
       final commit = repo.lookupCommit(head.target);