GitCommitBear.py: Require URL in commit message body

This ensures that the git commit contains a URL
that relates to an issue.

Fixes coala#1112

bears/vcs/git/GitCommitBear.py

@@ -3,6 +3,8 @@
 import shutil
 import os
 
+from urllib.parse import urlparse
+
 from coalib.bears.GlobalBear import GlobalBear
 from coalib.bears.requirements.PipRequirement import PipRequirement
 from coala_utils.ContextManagers import change_directory
@@ -197,6 +199,25 @@ def check_body(self, body,
                                'HEAD commit. Please add one.')
             return
 
+        urls = re.findall(r'(https|http?://\S+)', body)
+        has_good_url = False
+        for url in urls:
+            pieces = urlparse(url)
+            netloc = pieces.netloc
+            scheme = pieces.scheme
+            path = pieces.path
+            try:
+                assert all([scheme, netloc, path])
+                if netloc.find('github') != -1 and path.find('issues'):
+                    has_good_url = True
+            except AssertionError:
+                pass
+
+        if not has_good_url:
+            yield Result(self, 'No issue related URL found in the body at '
+                               'HEAD commit. Please add one.')
+            return
+
         ignore_regexes = [re.compile(regex) for regex in ignore_length_regex]
         if any((len(line) > body_line_length and
                 not any(regex.search(line) for regex in ignore_regexes))