Add Strict Metaschema Validation (#1101)

Improve schema validation.

This adds strict validation of config module definitions at testing
time, with plumbing included for future runtime validation. This
eliminates a class of bugs resulting from schemas that have definitions
that are incorrect, but get interpreted by jsonschema as
"additionalProperties" that are therefore ignored.

- Add strict meta-schema for jsonschema unit test validation
- Separate schema from module metadata structure
- Improve type annotations for various functions and data types

Cleanup:
- Remove unused jsonschema "required" elements 
- Eliminate manual memoization in schema.py:get_schema(),
        reference module.__doc__ directly

1 files changed, 19 insertions, 22 deletions

diff --git a/cloudinit/config/cc_write_files_deferred.py b/cloudinit/config/cc_write_files_deferred.py
index 0c75aa22..4fc8659c 100644
--- a/cloudinit/config/cc_write_files_deferred.py
+++ b/cloudinit/config/cc_write_files_deferred.py
@@ -4,34 +4,31 @@
 
 """Defer writing certain files"""
 
-from textwrap import dedent
-
 from cloudinit.config.schema import validate_cloudconfig_schema
 from cloudinit import util
 from cloudinit.config.cc_write_files import (
     schema as write_files_schema, write_files, DEFAULT_DEFER)
 
+# meta is not used in this module, but it remains as code documentation
+#
+# id: cc_write_files_deferred'
+# name: 'Write Deferred Files
+# distros: ['all'],
+# frequency: PER_INSTANCE,
+# title:
+#    write certain files, whose creation as been deferred, during
+#    final stage
+# description:
+#    This module is based on `'Write Files' <write-files>`__, and
+#    will handle all files from the write_files list, that have been
+#    marked as deferred and thus are not being processed by the
+#    write-files module.
+#
+#    *Please note that his module is not exposed to the user through
+#    its own dedicated top-level directive.*
+
+schema = write_files_schema
 
-schema = util.mergemanydict([
-    {
-        'id': 'cc_write_files_deferred',
-        'name': 'Write Deferred Files',
-        'title': dedent("""\
-            write certain files, whose creation as been deferred, during
-            final stage
-        """),
-        'description': dedent("""\
-            This module is based on `'Write Files' <write-files>`__, and
-            will handle all files from the write_files list, that have been
-            marked as deferred and thus are not being processed by the
-            write-files module.
-
-            *Please note that his module is not exposed to the user through
-            its own dedicated top-level directive.*
-        """)
-    },
-    write_files_schema
-])
 
 # Not exposed, because related modules should document this behaviour
 __doc__ = None