feat(merge): add ability to pass options to fileFromIndex(...) API method (#69)

lib/src/bindings/merge.dart

@@ -186,30 +186,39 @@ String mergeFile({
   libgit2.git_merge_file_input_init(theirsC, GIT_MERGE_FILE_INPUT_VERSION);
   ancestorC.ref.ptr = ancestor.toChar();
   ancestorC.ref.size = ancestor.length;
+  Pointer<Char> ancestorLabelC = nullptr;
   oursC.ref.ptr = ours.toChar();
   oursC.ref.size = ours.length;
+  Pointer<Char> oursLabelC = nullptr;
   theirsC.ref.ptr = theirs.toChar();
   theirsC.ref.size = theirs.length;
+  Pointer<Char> theirsLabelC = nullptr;
 
   final opts = calloc<git_merge_file_options>();
   libgit2.git_merge_file_options_init(opts, GIT_MERGE_FILE_OPTIONS_VERSION);
   opts.ref.favor = favor;
   opts.ref.flags = flags;
   if (ancestorLabel.isNotEmpty) {
-    opts.ref.ancestor_label = ancestorLabel.toChar();
+    ancestorLabelC = ancestorLabel.toChar();
+    opts.ref.ancestor_label = ancestorLabelC;
   }
   if (oursLabel.isNotEmpty) {
-    opts.ref.our_label = oursLabel.toChar();
+    oursLabelC = oursLabel.toChar();
+    opts.ref.our_label = oursLabelC;
   }
   if (theirsLabel.isNotEmpty) {
-    opts.ref.their_label = theirsLabel.toChar();
+    theirsLabelC = theirsLabel.toChar();
+    opts.ref.their_label = theirsLabelC;
   }
 
   libgit2.git_merge_file(out, ancestorC, oursC, theirsC, opts);
 
   calloc.free(ancestorC);
+  calloc.free(ancestorLabelC);
   calloc.free(oursC);
+  calloc.free(oursLabelC);
   calloc.free(theirsC);
+  calloc.free(theirsLabelC);
   calloc.free(opts);
 
   final result = out.ref.ptr.toDartString(length: out.ref.len);
@@ -226,17 +235,43 @@ String mergeFile({
 String mergeFileFromIndex({
   required Pointer<git_repository> repoPointer,
   required Pointer<git_index_entry>? ancestorPointer,
+  required String ancestorLabel,
   required Pointer<git_index_entry> oursPointer,
+  required String oursLabel,
   required Pointer<git_index_entry> theirsPointer,
+  required String theirsLabel,
+  required int favor,
+  required int flags,
 }) {
   final out = calloc<git_merge_file_result>();
+  final opts = calloc<git_merge_file_options>();
+  Pointer<Char> ancestorLabelC = nullptr;
+  Pointer<Char> oursLabelC = nullptr;
+  Pointer<Char> theirsLabelC = nullptr;
+
+  libgit2.git_merge_file_options_init(opts, GIT_MERGE_FILE_OPTIONS_VERSION);
+  opts.ref.favor = favor;
+  opts.ref.flags = flags;
+  if (ancestorLabel.isNotEmpty) {
+    ancestorLabelC = ancestorLabel.toChar();
+    opts.ref.ancestor_label = ancestorLabelC;
+  }
+  if (oursLabel.isNotEmpty) {
+    oursLabelC = oursLabel.toChar();
+    opts.ref.our_label = oursLabelC;
+  }
+  if (theirsLabel.isNotEmpty) {
+    theirsLabelC = theirsLabel.toChar();
+    opts.ref.their_label = theirsLabelC;
+  }
+
   final error = libgit2.git_merge_file_from_index(
     out,
     repoPointer,
     ancestorPointer ?? nullptr,
     oursPointer,
     theirsPointer,
-    nullptr,
+    opts,
   );
 
   late final String result;
@@ -244,6 +279,10 @@ String mergeFileFromIndex({
     result = out.ref.ptr.toDartString(length: out.ref.len);
   }
 
+  calloc.free(ancestorLabelC);
+  calloc.free(oursLabelC);
+  calloc.free(theirsLabelC);
+  calloc.free(opts);
   calloc.free(out);
 
   if (error < 0) {

lib/src/merge.dart

@@ -265,18 +265,43 @@ class Merge {
   /// given common [ancestor] as the baseline, producing a string that reflects
   /// the merge result containing possible conflicts.
   ///
+  /// [ancestorLabel] is optional label for the ancestor file side of the
+  /// conflict which will be prepended to labels in diff3-format merge files.
+  ///
+  /// [oursLabel] is optional label for our file side of the conflict which
+  /// will be prepended to labels in merge files.
+  ///
+  /// [theirsLabel] is optional label for their file side of the conflict which
+  /// will be prepended to labels in merge files.
+  ///
+  /// [favor] is one of the [GitMergeFileFavor] flags for handling conflicting
+  /// content. Defaults to [GitMergeFileFavor.normal].
+  ///
+  /// [flags] is a combination of [GitMergeFileFlag] flags. Defaults to
+  /// [GitMergeFileFlag.defaults].
+  ///
   /// Throws a [LibGit2Error] if error occured.
   static String fileFromIndex({
     required Repository repo,
     required IndexEntry? ancestor,
+    String ancestorLabel = '',
     required IndexEntry ours,
+    String oursLabel = '',
     required IndexEntry theirs,
+    String theirsLabel = '',
+    GitMergeFileFavor favor = GitMergeFileFavor.normal,
+    Set<GitMergeFileFlag> flags = const {GitMergeFileFlag.defaults},
   }) {
     return bindings.mergeFileFromIndex(
       repoPointer: repo.pointer,
       ancestorPointer: ancestor?.pointer,
+      ancestorLabel: ancestorLabel,
       oursPointer: ours.pointer,
+      oursLabel: oursLabel,
       theirsPointer: theirs.pointer,
+      theirsLabel: theirsLabel,
+      favor: favor.value,
+      flags: flags.fold(0, (acc, e) => acc | e.value),
     );
   }