GitCommitBear.py: Detect revert commits

This detects revert commits
and checks they have a reason as well.

Closes #337

bears/vcs/git/GitCommitBear.py

@@ -67,6 +67,12 @@ def check_prerequisites(cls):
         else:
             return True
 
+    @classmethod
+    def get_revert_checks_metadata(cls):
+        return FunctionMetadata.from_function(
+            cls.check_revert,
+            omit={'self', 'shortlog', 'body'})
+
     @classmethod
     def get_shortlog_checks_metadata(cls):
         return FunctionMetadata.from_function(
@@ -91,6 +97,7 @@ def get_metadata(cls):
             FunctionMetadata.from_function(
                 cls.run,
                 omit={'self', 'dependency_results'}),
+            cls.get_revert_checks_metadata(),
             cls.get_shortlog_checks_metadata(),
             cls.get_body_checks_metadata(),
             cls.get_issue_checks_metadata())
@@ -112,8 +119,7 @@ def get_host_from_remotes():
         netloc = parsed_url.host
         return netloc.split('.')[0]
 
-    def run(self,
-            allow_empty_commit_message: bool = False,
+    def run(self, allow_empty_commit_message: bool = False,
             **kwargs):
         """
         Check the current git commit message at HEAD.
@@ -141,6 +147,10 @@ def run(self,
                 yield Result(self, 'HEAD commit has no message.')
             return
 
+        yield from self.check_revert(
+            shortlog,
+            body,
+            **self.get_revert_checks_metadata().filter_parameters(kwargs))
         yield from self.check_shortlog(
             shortlog,
             **self.get_shortlog_checks_metadata().filter_parameters(kwargs))
@@ -151,6 +161,47 @@ def run(self,
             body,
             **self.get_issue_checks_metadata().filter_parameters(kwargs))
 
+    def check_revert(self, shortlog, body,
+                     allow_revert_commits_without_reason: bool = False,):
+        """
+        Validates revert commits.
+
+        :param shortlog:                 The shortlog message string.
+        :param body:          The body of the commit message of HEAD.
+        :param allow_revert_commits_without_reason: Whether reason is
+                                           needed for revert commits.
+        """
+        REVERT_REGEX = re.compile(r'(Revert ")([\S+\s*]*)("$)')
+        HEADLINE_REGEX = re.compile(r'(^This reverts commit )([0-9a-f]{40})')
+
+        if REVERT_REGEX.match(shortlog):
+            reverted_shortlog = re.search(REVERT_REGEX, shortlog).group(2)
+
+            body = body.strip('\n')
+            blankline = body.find('\n\n')
+            headline = body[:blankline] if blankline != -1 else body
+
+            if not HEADLINE_REGEX.match(headline):
+                yield Result(self, 'Invalid revert commit.')
+                return
+
+            commit_sha = re.search(HEADLINE_REGEX, headline).group(2)
+            command = ('git log -n 1 ' +
+                       str(commit_sha) + ' --pretty=%B')
+            rstdout, _ = run_shell_command(command)
+            rstdout = rstdout.rstrip('\n')
+            rpos = rstdout.find('\n')
+            old_shortlog = rstdout[:rpos] if rpos != -1 else rstdout
+
+            if old_shortlog != reverted_shortlog:
+                yield Result(self, 'Shortlog of revert commit does '
+                             'not match the original commit.')
+
+            reason = body[blankline+1:] if blankline != -1 else ''
+
+            if not allow_revert_commits_without_reason and len(reason) == 0:
+                yield Result(self, 'Revert commit does not have a reason.')
+
     def check_shortlog(self, shortlog,
                        shortlog_length: int = 50,
                        shortlog_regex: str = '',

tests/vcs/git/GitCommitBearTest.py

@@ -95,11 +95,13 @@ def test_get_metadata(self):
         metadata = GitCommitBear.get_metadata()
         self.assertEqual(
             metadata.name,
-            "<Merged signature of 'run', 'check_shortlog', 'check_body'"
-            ", 'check_issue_reference'>")
+            "<Merged signature of 'run', 'check_revert', 'check_shortlog'"
+            ", 'check_body', 'check_issue_reference'>")
 
         # Test if at least one parameter of each signature is used.
         self.assertIn('allow_empty_commit_message', metadata.optional_params)
+        self.assertIn('allow_revert_commits_without_reason',
+                      metadata.optional_params)
         self.assertIn('shortlog_length', metadata.optional_params)
         self.assertIn('body_line_length', metadata.optional_params)
         self.assertIn('body_close_issue', metadata.optional_params)
@@ -125,6 +127,60 @@ def test_empty_message(self):
                          [])
         self.assert_no_msgs()
 
+    def test_revert_checks(self):
+        self.git_commit('Test commit')
+        commit_hash, _ = run_shell_command('git rev-parse HEAD')
+        self.git_commit('Revert "Test commit"\n\n'
+                        'Abcdef blablabla commit ' + str(commit_hash) + '\n\n'
+                        'Reason for the revert commit is explained here.\n')
+        self.assertEqual(self.run_uut(),
+                         ['Invalid revert commit.'])
+        self.assert_no_msgs()
+
+        self.git_commit('Test commit1\n\n'
+                        'This is body of test commit1\n')
+        commit_hash, _ = run_shell_command('git rev-parse HEAD')
+
+        self.git_commit('Revert "Another Test commit2"\n\n'
+                        'This reverts commit ' + str(commit_hash) + '\n\n'
+                        'Reason for the revert commit is explained here.\n')
+        self.assertEqual(
+            self.run_uut(),
+            ['Shortlog of revert commit does not match the original commit.'])
+        self.assert_no_msgs()
+
+        self.git_commit('Test commit3')
+        commit_hash, _ = run_shell_command('git rev-parse HEAD')
+        self.git_commit('Revert "Test commit3"\n\n'
+                        'This reverts commit ' + str(commit_hash) + '\n\n')
+        self.assertEqual(self.run_uut(),
+                         ['Revert commit does not have a reason.'])
+        self.assert_no_msgs()
+
+        self.git_commit('Revert "Test commit3"\n\n'
+                        'This reverts commit ' + str(commit_hash) + '\n\n')
+        self.assertEqual(
+            self.run_uut(allow_revert_commits_without_reason=True),
+            [])
+        self.assert_no_msgs()
+
+        self.git_commit('Revert "Test commit3"\n\n'
+                        'This reverts commit ' + str(commit_hash) + '\n\n'
+                        'Reason for the revert commit is explained here.\n')
+        self.assertEqual(self.run_uut(), [])
+        self.assert_no_msgs()
+
+        self.git_commit('Test commit4\n\n'
+                        'This is body of test commit1\n')
+        commit_hash, _ = run_shell_command('git rev-parse HEAD')
+        self.git_commit('Revert "Another Test commit5"\n\n'
+                        'This reverts commit ' + str(commit_hash) + '\n\n'
+                        'Reason for the revert commit is explained here.\n')
+        self.assertEqual(
+            self.run_uut(),
+            ['Shortlog of revert commit does not match the original commit.'])
+        self.assert_no_msgs()
+
     @unittest.mock.patch('bears.vcs.git.GitCommitBear.run_shell_command',
                          return_value=('one-liner-message\n', ''))
     def test_pure_oneliner_message(self, patch):