GitCommitBear.py: Require URL in commit 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
@@ -175,6 +177,7 @@ def check_imperative(self, paragraph):
     def check_body(self, body,
                    body_line_length: int=72,
                    force_body: bool=False,
+                   should_contain_url: bool=False,
                    ignore_length_regex: typed_list(str)=()):
         """
         Checks the given commit body.
@@ -197,6 +200,27 @@ def check_body(self, body,
                                'HEAD commit. Please add one.')
             return
 
+        if should_contain_url:
+            urls = re.findall(r'(https?://\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))