--- a/python/mozbuild/mozbuild/vendor_aom.py
+++ b/python/mozbuild/mozbuild/vendor_aom.py
@@ -195,17 +195,17 @@ Please check manually and update the ven
                          cwd=target)
 
     def check_modified_files(self):
         '''
         Ensure that there aren't any uncommitted changes to files
         in the working copy, since we're going to change some state
         on the user.
         '''
-        modified = self.repository.get_modified_files()
+        modified = self.repository.get_changed_files('M')
         if modified:
             self.log(logging.ERROR, 'modified_files', {},
                      '''You have uncommitted changes to the following files:
 
 {files}
 
 Please commit or stash these changes before vendoring, or re-run with `--ignore-modified`.
 '''.format(files='\n'.join(sorted(modified))))

--- a/python/mozbuild/mozbuild/vendor_rust.py
+++ b/python/mozbuild/mozbuild/vendor_rust.py
@@ -55,17 +55,17 @@ class VendorRust(MozbuildObject):
 
     def check_modified_files(self):
         '''
         Ensure that there aren't any uncommitted changes to files
         in the working copy, since we're going to change some state
         on the user. Allow changes to Cargo.{toml,lock} since that's
         likely to be a common use case.
         '''
-        modified = [f for f in self.repository.get_modified_files() if os.path.basename(f) not in ('Cargo.toml', 'Cargo.lock')]
+        modified = [f for f in self.repository.get_changed_files('M') if os.path.basename(f) not in ('Cargo.toml', 'Cargo.lock')]
         if modified:
             self.log(logging.ERROR, 'modified_files', {},
                      '''You have uncommitted changes to the following files:
 
 {files}
 
 Please commit or stash these changes before vendoring, or re-run with `--ignore-modified`.
 '''.format(files='\n'.join(sorted(modified))))
@@ -291,17 +291,17 @@ license file's hash.
             sys.exit(1)
 
         self.repository.add_remove_files(vendor_dir)
 
         # 100k is a reasonable upper bound on source file size.
         FILESIZE_LIMIT = 100 * 1024
         large_files = set()
         cumulative_added_size = 0
-        for f in self.repository.get_added_files():
+        for f in self.repository.get_changed_files('A'):
             path = mozpath.join(self.topsrcdir, f)
             size = os.stat(path).st_size
             cumulative_added_size += size
             if size > FILESIZE_LIMIT:
                 large_files.add(f)
 
         # Forcefully complain about large files being added, as history has
         # shown that large-ish files typically are not needed.

--- a/python/mozversioncontrol/mozversioncontrol/__init__.py
+++ b/python/mozversioncontrol/mozversioncontrol/__init__.py
@@ -53,16 +53,17 @@ class Repository(object):
 
     __metaclass__ = abc.ABCMeta
 
     def __init__(self, path, tool):
         self.path = os.path.abspath(path)
         self._tool = get_tool_path(tool)
         self._env = os.environ.copy()
         self._version = None
+        self._valid_diff_filter = ('m', 'a', 'd')
 
     def __enter__(self):
         return self
 
     def __exit__(self, exc_type, exc_value, exc_tb):
         pass
 
     def _run(self, *args):
@@ -93,24 +94,32 @@ class Repository(object):
 
         A sparse checkout is defined as a working directory that only
         materializes a subset of files in a given revision.
 
         Returns a bool.
         """
 
     @abc.abstractmethod
-    def get_modified_files(self):
-        '''Return a list of files that are modified in this repository's
-        working copy.'''
+    def get_changed_files(self, diff_filter, mode='unstaged'):
+        """Return a list of files that are changed in this repository's
+        working copy.
+
+        ``diff_filter`` controls which kinds of modifications are returned.
+        It is a string which may only contain the following characters:
 
-    @abc.abstractmethod
-    def get_added_files(self):
-        '''Return a list of files that are added in this repository's
-        working copy.'''
+            A - Include files that were added
+            D - Include files that were deleted
+            M - Include files that were modified
+
+        By default, all three will be included.
+
+        ``mode`` can be one of 'unstaged', 'staged' or 'all'. Only has an
+        affect on git. Defaults to 'unstaged'.
+        """
 
     @abc.abstractmethod
     def add_remove_files(self, path):
         '''Add and remove files under `path` in this repository's working copy.
         '''
 
     @abc.abstractmethod
     def forget_add_remove_files(self, path):
@@ -191,23 +200,31 @@ class HgRepository(Repository):
             st = os.stat(sparse)
             return st.st_size > 0
         except OSError as e:
             if e.errno != errno.ENOENT:
                 raise
 
             return False
 
-    def get_modified_files(self):
-        # Use --no-status to print just the filename.
-        return self._run('status', '--modified', '--no-status').splitlines()
+    def _format_diff_filter(self, diff_filter):
+        df = diff_filter.lower()
+        assert all(f in self._valid_diff_filter for f in df)
+
+        # Mercurial uses 'r' to denote removed files whereas git uses 'd'.
+        if 'd' in df:
+            df.replace('d', 'r')
 
-    def get_added_files(self):
+        return df.lower()
+
+    def get_changed_files(self, diff_filter='ADM', mode='unstaged'):
+        df = self._format_diff_filter(diff_filter)
+
         # Use --no-status to print just the filename.
-        return self._run('status', '--added', '--no-status').splitlines()
+        return self._run('status', '--no-status', '-{}'.format(df)).splitlines()
 
     def add_remove_files(self, path):
         args = ['addremove', path]
         if self.tool_version >= b'3.9':
             args = ['--config', 'extensions.automv='] + args
         self._run(*args)
 
     def forget_add_remove_files(self, path):
@@ -240,21 +257,26 @@ class GitRepository(Repository):
     @property
     def name(self):
         return 'git'
 
     def sparse_checkout_present(self):
         # Not yet implemented.
         return False
 
-    def get_modified_files(self):
-        return self._run('diff', '--diff-filter=M', '--name-only').splitlines()
+    def get_changed_files(self, diff_filter='ADM', mode='unstaged'):
+        assert all(f.lower() in self._valid_diff_filter for f in diff_filter)
 
-    def get_added_files(self):
-        return self._run('diff', '--diff-filter=A', '--name-only').splitlines()
+        cmd = ['diff', '--diff-filter={}'.format(diff_filter.upper()), '--name-only']
+        if mode == 'staged':
+            cmd.append('--cached')
+        elif mode == 'all':
+            cmd.append('HEAD')
+
+        return self._run(*cmd).splitlines()
 
     def add_remove_files(self, path):
         self._run('add', path)
 
     def forget_add_remove_files(self, path):
         self._run('reset', path)
 
     def get_files_in_working_directory(self):