Exit github_deploy if output folder is committed on source branch.

nikola/plugins/command/github_deploy.py

@@ -50,13 +50,15 @@ class CommandGitHubDeploy(Command):
         It performs the following actions:
 
         1. Ensure that your site is a git repository, and git is on the PATH.
-        2. Check for changes, and prompt the user to continue, if required.
-        3. Build the site
-        4. Clean any files that are "unknown" to Nikola.
-        5. Create a deploy branch, if one doesn't exist.
-        6. Commit the output to this branch.  (NOTE: Any untracked source
+        2. Ensure that the output directory is not committed on the
+           source branch.
+        3. Check for changes, and prompt the user to continue, if required.
+        4. Build the site
+        5. Clean any files that are "unknown" to Nikola.
+        6. Create a deploy branch, if one doesn't exist.
+        7. Commit the output to this branch.  (NOTE: Any untracked source
            files, may get committed at this stage, on the wrong branch!)
-        7. Push and deploy!
+        8. Push and deploy!
 
         NOTE: This command needs your site to be a git repository, with a
         master branch (or a different branch, configured using
@@ -91,6 +93,8 @@ def _execute(self, command, args):
 
         self._ensure_git_repo()
 
+        self._exit_if_output_committed()
+
         if not self._prompt_continue():
             return
 
@@ -229,6 +233,24 @@ def _ensure_git_repo(self):
                 )
                 sys.exit(1)
 
+    def _exit_if_output_committed(self):
+        """ Exit if the output folder is committed on the source branch. """
+
+        source = self._source_branch
+        subprocess.check_call(['git', 'checkout', source])
+
+        output_folder = self.site.config['OUTPUT_FOLDER']
+        output_log = subprocess.check_output(
+            ['git', 'ls-files', '--', output_folder]
+        )
+
+        if len(output_log.strip()) > 0:
+            self.logger.error(
+                'Output folder is committed on the source branch. '
+                'Cannot proceed until it is removed.'
+                )
+            sys.exit(1)
+
     def _prompt_continue(self):
         """ Show uncommitted changes, and ask if user wants to continue. """