Add remove modification

This modification can be used to remove files from the distgit repo:

```yaml
content:
  source:
    modifications:
    - action: remove
      glob: **/*.txt  # remove all .txt files from the distgit repo
```

doozerlib/source_modifications.py

@@ -4,6 +4,7 @@
 
 import requests
 import yaml
+from pathlib import Path
 
 from doozerlib.exceptions import DoozerFatalError
 from doozerlib.exectools import cmd_assert
@@ -192,3 +193,40 @@ def act(self, *args, **kwargs):
 
 
 SourceModifierFactory.MODIFICATIONS["command"] = CommandModifier
+
+
+class RemoveModifier(object):
+    """ A source modifier that supports removing files from the distgit repository.
+    """
+
+    def __init__(self, *args, **kwargs):
+        """ Initialize CommandModifier
+        :param command: a `str` or `list` of the command with arguments
+        """
+        self.glob = kwargs["glob"]
+
+    def act(self, *args, **kwargs):
+        """ Run the command
+        :param context: A context dict. `context.set_env` is a `dict` of env vars to set for command (overriding existing).
+        """
+        context = kwargs["context"]
+        component = context["component_name"]
+        distgit_path = Path(context['distgit_path'])
+        ceiling_dir = Path(kwargs["ceiling_dir"])
+
+        LOGGER.info("Distgit repo %s: Running 'remove' modification action...", component)
+        removed = []
+        for path in distgit_path.rglob(self.glob):
+            if not is_in_directory(path, ceiling_dir):
+                raise PermissionError("Removing a file from a location outside of directory {} is not allowed.".format(ceiling_dir))
+            relative_path = str(path.relative_to(distgit_path))
+            LOGGER.info("Distgit repo %s: Removing %s", component, relative_path)
+            path.unlink()
+            removed.append(relative_path)
+        if len(removed):
+            LOGGER.info("Distgit repo %s: %s files have been removed:\n%s", component, len(removed), "\n".join(removed))
+        else:
+            LOGGER.warning("Distgit repo %s: No files matching glob `%s`", component, self.glob)
+
+
+SourceModifierFactory.MODIFICATIONS["remove"] = RemoveModifier

tests/test_source_modifications.py

@@ -8,7 +8,8 @@
 import mock
 import yaml.scanner
 
-from doozerlib.source_modifications import AddModifier, SourceModifierFactory
+from doozerlib.source_modifications import (AddModifier, RemoveModifier,
+                                            SourceModifierFactory)
 
 
 class SourceModifierFactoryTestCase(unittest.TestCase):
@@ -90,5 +91,43 @@ def test_act_failed_with_invalid_yaml(self):
                 modifier.act(ceiling_dir=self.temp_dir, session=session, context=context)
 
 
+class TestRemoveModifier(unittest.TestCase):
+    def test_remove_file(self):
+        distgit_path = pathlib.Path("/path/to/distgit")
+        modifier = RemoveModifier(glob="**/*.txt", distgit_path=distgit_path)
+        context = {
+            "component_name": "foo",
+            "kind": "Dockerfile",
+            "content": "whatever",
+            "distgit_path": distgit_path,
+        }
+        with mock.patch.object(pathlib.Path, "rglob") as rglob, mock.patch.object(pathlib.Path, "unlink") as unlink:
+            rglob.return_value = map(lambda path: distgit_path.joinpath(path), [
+                "1.txt",
+                "a/2.txt",
+                "b/c/d/e/3.txt",
+            ])
+            modifier.act(context=context, ceiling_dir=str(distgit_path))
+            unlink.assert_called()
+
+    def test_remove_file_outside_of_distgit_dir(self):
+        distgit_path = pathlib.Path("/path/to/distgit")
+        modifier = RemoveModifier(glob="**/*.txt", distgit_path=distgit_path)
+        context = {
+            "component_name": "foo",
+            "kind": "Dockerfile",
+            "content": "whatever",
+            "distgit_path": distgit_path,
+        }
+        with mock.patch.object(pathlib.Path, "rglob") as rglob:
+            rglob.return_value = map(lambda path: pathlib.Path("/some/other/path").joinpath(path), [
+                "1.txt",
+                "a/2.txt",
+                "b/c/d/e/3.txt",
+            ])
+            with self.assertRaises(PermissionError):
+                modifier.act(context=context, ceiling_dir=str(distgit_path))
+
+
 if __name__ == "__main__":
     unittest.main()