Use git interpret-trailers for trailers property

The whitespace handling and trailer selection isn't very trivial or good
documented. It therefore seemed easier and less error prone to just call
git to parse the message for the trailers section and remove superfluos
whitespaces.

git/objects/commit.py

@@ -4,8 +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
+from subprocess import Popen, PIPE
 from gitdb import IStream
 from git.util import (
     hex_to_bin,
@@ -14,6 +13,7 @@
     finalize_process
 )
 from git.diff import Diffable
+from git.cmd import Git
 
 from .tree import Tree
 from . import base
@@ -322,10 +322,10 @@ def trailers(self) -> Dict:
 
         Git messages can contain trailer information that are similar to RFC 822
         e-mail headers (see: https://git-scm.com/docs/git-interpret-trailers).
-        
-        The trailer is thereby the last paragraph (seperated by a empty line
-        from the subject/body). This trailer paragraph must contain a ``:`` as
-        seperator for key and value in every line.
+
+        This funcions calls ``git interpret-trailers --parse`` onto the message
+        to extract the trailer information. The key value pairs are stripped of
+        leading and trailing whitespaces before they get saved into a dictionary.
 
         Valid message with trailer:
 
@@ -338,20 +338,29 @@ def trailers(self) -> Dict:
             another information
 
             key1: value1
-            key2: value2
+            key2 :    value 2 with inner spaces
+
+        dictionary will look like this:
+        .. code-block::
+
+            {
+                "key1": "value1",
+                "key2": "value 2 with inner spaces"
+            }
 
         :return: Dictionary containing whitespace stripped trailer information
+
         """
-        d: Dict[str, str] = {}
-        match = re.search(r".+^\s*$\n([\w\n\s:]+?)\s*\Z", str(self.message), re.MULTILINE | re.DOTALL)
-        if match is None:
-            return d
-        last_paragraph = match.group(1)
-        if not all(':' in line for line in last_paragraph.split('\n')):
-            return d
-        for line in last_paragraph.split('\n'):
-            key, value = line.split(':', 1)
-            d[key.strip()] = value.strip()
+        d = {}
+        cmd = ['git', 'interpret-trailers', '--parse']
+        proc: Git.AutoInterrupt = self.repo.git.execute(cmd, as_process=True, istream=PIPE)  # type: ignore
+        trailer: str = proc.communicate(str(self.message).encode())[0].decode()
+        if trailer.endswith('\n'):
+            trailer = trailer[0:-1]
+        if trailer != '':
+            for line in trailer.split('\n'):
+                key, value = line.split(':', 1)
+                d[key.strip()] = value.strip()
         return d
 
     @ classmethod

test/test_commit.py

@@ -435,14 +435,14 @@ def test_trailers(self):
         KEY_1 = "Hello"
         VALUE_1 = "World"
         KEY_2 = "Key"
-        VALUE_2 = "Value"
+        VALUE_2 = "Value with inner spaces"
 
         # Check if KEY 1 & 2 with Value 1 & 2 is extracted from multiple msg variations
         msgs = []
         msgs.append(f"Subject\n\n{KEY_1}: {VALUE_1}\n{KEY_2}: {VALUE_2}\n")
         msgs.append(f"Subject\n  \nSome body of a function\n \n{KEY_1}: {VALUE_1}\n{KEY_2}: {VALUE_2}\n")
         msgs.append(f"Subject\n  \nSome body of a function\n\nnon-key: non-value\n\n{KEY_1}: {VALUE_1}\n{KEY_2}: {VALUE_2}\n")
-        msgs.append(f"Subject\n  \nSome multiline\n body of a function\n\nnon-key: non-value\n\n{KEY_1}: {VALUE_1}\n{KEY_2}: {VALUE_2}\n")
+        msgs.append(f"Subject\n  \nSome multiline\n body of a function\n\nnon-key: non-value\n\n{KEY_1}: {VALUE_1}\n{KEY_2} :      {VALUE_2}\n")
 
         for msg in msgs:
             commit = self.rorepo.commit('master')