GitCommitBear.py: Require URL in commit body

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

Fixes coala#1112

.coafile

@@ -29,6 +29,8 @@ bears = SpaceConsistencyBear
 
 [commit]
 bears = GitCommitBear
+host_used = github
+contains_url = True
 shortlog_trailing_period = False
 shortlog_regex = ([^:]*|[^:]+: [A-Z0-9*].*)
 

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
@@ -50,7 +52,9 @@ def get_metadata(cls):
             cls.get_shortlog_checks_metadata(),
             cls.get_body_checks_metadata())
 
-    def run(self, allow_empty_commit_message: bool = False, **kwargs):
+    def run(self,
+            allow_empty_commit_message: bool = False,
+            **kwargs):
         """
         Check the current git commit message at HEAD.
 
@@ -175,6 +179,8 @@ def check_imperative(self, paragraph):
     def check_body(self, body,
                    body_line_length: int=72,
                    force_body: bool=False,
+                   host_used: str='',
+                   contains_url: bool=False,
                    ignore_length_regex: typed_list(str)=()):
         """
         Checks the given commit body.
@@ -183,6 +189,9 @@ def check_body(self, body,
         :param body_line_length:    The maximum line-length of the body. The
                                     newline character at each line end does not
                                     count to the length.
+        :param host_used:           The version control system used.
+        :param contains_url:        Whether the body contains a issue related
+                                    URL or not.
         :param force_body:          Whether a body shall exist or not.
         :param ignore_length_regex: Lines matching each of the regular
                                     expressions in this list will be ignored.
@@ -197,6 +206,27 @@ def check_body(self, body,
                                'HEAD commit. Please add one.')
             return
 
+        if contains_url:
+            urls = re.findall(r'(https?://\S+)', '\n'.join(body))
+            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])
+                except AssertionError:
+                    pass
+                if netloc.find(host_used) != -1 and path.find('issues') != -1:
+                    good_url = True
+
+            if not 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))