In Git.unstaged_files, handle the case when there are no changes.

third_party/WebKit/Tools/Scripts/webkitpy/common/checkout/scm/git.py

 # Copyright (c) 2009, 2010, 2011 Google Inc. All rights reserved.
 # Copyright (c) 2009 Apple Inc. All rights reserved.
 #
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
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 #     * Redistributions in binary form must reproduce the above
@@ skipping 103 matching lines @@
 
     def unstaged_changes(self):
         """Lists files with unstaged changes, including untracked files.
 
         Returns a dict mapping modified file paths (relative to checkout root)
         to one-character codes identifying the change, e.g. 'M' for modified,
         'D' for deleted, '?' for untracked.
         """
         # `git status -z` is a version of `git status -s`, that's recommended
         # for machine parsing. Lines are terminated with NUL rather than LF.
+        change_lines = self._run_git(['status', '-z']).rstrip('\x00')
+        if not change_lines:
+            return {}  # No changes.
         unstaged_changes = {}

[qyearsley, 2016/12/28 18:47:20]

Here, if there are no changes, then change_lines is [''], and line[1] hits an
IndexError.

-        change_lines = self._run_git(['status', '-z']).rstrip('\x00').split('\x00')
-        for line in change_lines:
+        for line in change_lines.split('\x00'):
+            assert len(line) > 4, 'Unexpected change line format %s' % line
             if line[1] == ' ':
                 continue  # Already staged for commit.
             path = line[3:]
             unstaged_changes[path] = line[1]
         return unstaged_changes
 
     def status_command(self):
         # git status returns non-zero when there are changes, so we use git diff name --name-status HEAD instead.
         # No file contents printed, thus utf-8 autodecoding in self.run is fine.
         return [self.executable_name, "diff", "--name-status", "--no-renames", "HEAD"]
@@ skipping 211 matching lines @@
         if self.current_branch() != self._branch_tracking_remote_master():
             return False
         if len(self._local_commits(self._branch_tracking_remote_master())) > 0:
             return False
         return True
 
     def ensure_cleanly_tracking_remote_master(self):
         self._discard_working_directory_changes()
         self._run_git(['checkout', '-q', self._branch_tracking_remote_master()])
         self._discard_local_commits()