feat(blame): add binding and api method for git_blame_buffer (#20)

lib/src/bindings/blame.dart

@@ -58,6 +58,38 @@ Pointer<git_blame> file({
   }
 }
 
+/// Get blame data for a file that has been modified in memory. The [reference]
+/// parameter is a pre-calculated blame for the in-odb history of the file.
+/// This means that once a file blame is completed (which can be expensive),
+/// updating the buffer blame is very fast.
+///
+/// Lines that differ between the buffer and the committed version are marked
+/// as having a zero OID for their finalCommitOid.
+///
+/// Throws a [LibGit2Error] if error occured.
+Pointer<git_blame> buffer({
+  required Pointer<git_blame> reference,
+  required String buffer,
+}) {
+  final out = calloc<Pointer<git_blame>>();
+  final bufferC = buffer.toNativeUtf8().cast<Int8>();
+  final error = libgit2.git_blame_buffer(
+    out,
+    reference,
+    bufferC,
+    buffer.length,
+  );
+
+  calloc.free(bufferC);
+
+  if (error < 0) {
+    calloc.free(out);
+    throw LibGit2Error(libgit2.git_error_last());
+  } else {
+    return out.value;
+  }
+}
+
 /// Gets the number of hunks that exist in the blame structure.
 int hunkCount(Pointer<git_blame> blame) {
   return libgit2.git_blame_get_hunk_count(blame);

lib/src/blame.dart

@@ -59,6 +59,23 @@ class Blame with IterableMixin<BlameHunk> {
     );
   }
 
+  /// Returns blame data for a file that has been modified in memory. The
+  /// [reference] parameter is a pre-calculated blame for the in-odb history of
+  /// the file.
+  /// This means that once a file blame is completed (which can be expensive),
+  /// updating the buffer blame is very fast.
+  ///
+  /// Lines that differ between the buffer and the committed version are marked
+  /// as having a zero Oid for their finalCommitOid.
+  ///
+  /// Throws a [LibGit2Error] if error occured.
+  Blame.buffer({required Blame reference, required String buffer}) {
+    _blamePointer = bindings.buffer(
+      reference: reference._blamePointer,
+      buffer: buffer,
+    );
+  }
+
   /// Pointer to memory address for allocated blame object.
   late final Pointer<git_blame> _blamePointer;
 
@@ -117,8 +134,11 @@ class BlameHunk {
 
   /// Author of [finalCommitOid]. If [GitBlameFlag.useMailmap] has been
   /// specified, it will contain the canonical real name and email address.
-  Signature get finalCommitter =>
+  Signature? get finalCommitter {
-      Signature(_blameHunkPointer.ref.final_signature);
+    return _blameHunkPointer.ref.final_signature == nullptr
+        ? null
+        : Signature(_blameHunkPointer.ref.final_signature);
+  }
 
   /// [Oid] of the commit where this line was last changed.
   Oid get finalCommitOid => Oid.fromRaw(_blameHunkPointer.ref.final_commit_id);
@@ -129,8 +149,11 @@ class BlameHunk {
 
   /// Author of [originCommitOid]. If [GitBlameFlag.useMailmap] has been
   /// specified, it will contain the canonical real name and email address.
-  Signature get originCommitter =>
+  Signature? get originCommitter {
-      Signature(_blameHunkPointer.ref.orig_signature);
+    return _blameHunkPointer.ref.orig_signature == nullptr
+        ? null
+        : Signature(_blameHunkPointer.ref.orig_signature);
+  }
 
   /// [Oid] of the commit where this hunk was found. This will usually be the
   /// same as [finalCommitOid], except when

test/blame_test.dart

@@ -88,6 +88,31 @@ void main() {
       expect(() => repo.blame(path: 'invalid'), throwsA(isA<LibGit2Error>()));
     });
 
+    test('returns blame for buffer', () {
+      final blame = repo.blame(path: 'feature_file');
+      expect(blame.length, 2);
+
+      final bufferBlame = Blame.buffer(reference: blame, buffer: ' ');
+      final blameHunk = bufferBlame.first;
+      expect(bufferBlame.length, 1);
+      expect(blameHunk.originCommitOid.sha, '0' * 40);
+      expect(blameHunk.originCommitter, null);
+      expect(blameHunk.finalCommitOid.sha, '0' * 40);
+      expect(blameHunk.finalCommitter, null);
+
+      bufferBlame.free();
+      blame.free();
+    });
+
+    test('throws when trying to get blame for empty buffer', () {
+      final blame = repo.blame(path: 'feature_file');
+      expect(
+        () => Blame.buffer(reference: blame, buffer: ''),
+        throwsA(isA<LibGit2Error>()),
+      );
+      blame.free();
+    });
+
     test(
         'successfully gets the blame for provided file with '
         'minMatchCharacters set', () {