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, 7 insertions, 4 deletions

diff --git a/cloudinit/config/cc_apt_configure.py b/cloudinit/config/cc_apt_configure.py
index 86d0feae..2e844c2c 100644
--- a/cloudinit/config/cc_apt_configure.py
+++ b/cloudinit/config/cc_apt_configure.py
@@ -14,8 +14,7 @@ import re
 import pathlib
 from textwrap import dedent
 
-from cloudinit.config.schema import (
-    get_schema_doc, validate_cloudconfig_schema)
+from cloudinit.config.schema import get_meta_doc, validate_cloudconfig_schema
 from cloudinit import gpg
 from cloudinit import log as logging
 from cloudinit import subp
@@ -75,7 +74,8 @@ mirror_property = {
         }
     }
 }
-schema = {
+
+meta = {
     'id': 'cc_apt_configure',
     'name': 'Apt Configure',
     'title': 'Configure apt for the user',
@@ -155,6 +155,9 @@ schema = {
                       <key data>
                       ------END PGP PUBLIC KEY BLOCK-------""")],
     'frequency': frequency,
+}
+
+schema = {
     'type': 'object',
     'properties': {
         'apt': {
@@ -398,7 +401,7 @@ schema = {
     }
 }
 
-__doc__ = get_schema_doc(schema)
+__doc__ = get_meta_doc(meta, schema)
 
 
 # place where apt stores cached repository data