Add commit co-authors support

AUTHORS

@@ -48,4 +48,5 @@ Contributors are:
 -Hiroki Tokunaga <tokusan441 _at_ gmail.com>
 -Julien Mauroy <pro.julien.mauroy _at_ gmail.com>
 -Patrick Gerard
+-Luke Twist <[email protected]>
 Portions derived from other open source works and are clearly marked.

git/objects/commit.py

@@ -4,6 +4,7 @@
 # This module is part of GitPython and is released under
 # the BSD License: http://www.opensource.org/licenses/bsd-license.php
 import datetime
+import re
 from subprocess import Popen, PIPE
 from gitdb import IStream
 from git.util import hex_to_bin, Actor, Stats, finalize_process
@@ -738,3 +739,24 @@ def _deserialize(self, stream: BytesIO) -> "Commit":
         return self
 
     # } END serializable implementation
+
+    @property
+    def co_authors(self) -> List[Actor]:
+        """
+        Search the commit message for any co-authors of this commit.
+        Details on co-authors: https://github.blog/2018-01-29-commit-together-with-co-authors/
+
+        :return: List of co-authors for this commit (as Actor objects).
+        """
+        co_authors = []
+
+        if self.message:
+            results = re.findall(
+                r"^Co-authored-by: ((?:\w|\-| ){0,38} <\S*>)$",
+                self.message,
+                re.MULTILINE,
+            )
+            for author_string in results:
+                co_authors.append(Actor._from_string(author_string))
+
+        return co_authors

test/test_commit.py

@@ -509,3 +509,18 @@ def test_trailers(self):
         assert KEY_1 not in commit.trailers.keys()
         assert KEY_2 in commit.trailers.keys()
         assert commit.trailers[KEY_2] == VALUE_2
+
+    def test_commit_co_authors(self):
+        commit = copy.copy(self.rorepo.commit("4251bd5"))
+        commit.message = """Commit message
+
+Co-authored-by: Test User 1 <[email protected]>
+Co-authored-by: test_user_2 <[email protected]>
+Co_authored_by: test_user_x <[email protected]>
+Co-authored-by: test_user_y <poorly formatted email @github.com>
+Co-authored-by: test_user_3 <[email protected]>"""
+        assert commit.co_authors == [
+            Actor("Test User 1", "[email protected]"),
+            Actor("test_user_2", "[email protected]"),
+            Actor("test_user_3", "[email protected]"),
+        ]