Fix freeze() with YAML anchors usage

YAML parser creates object references when using YAML anchors.
When one object in the tree is frozen, it affects all references to it,
so when the traversal encounters a reference to already frozen object,
it must not attempt to freeze it again. This commit enhances the type
checks and skips freezing of already frozen objects.

Author: MichalHaluza

src/cdn_definitions/_impl/__init__.py

@@ -34,6 +34,12 @@ def freeze(node):
     """
     Converts dict to frozendict and list to frozenlist.
     """
+    if isinstance(node, (frozenlist, frozendict)):
+        # YAML parser creates object references when using YAML anchors.
+        # When one object in the tree is frozen, it affects all references to it,
+        # so when the traversal encounters a reference to already frozen object,
+        # it must not attempt to freeze it again.
+        return node
     if isinstance(node, list):
         # Iterating using index instead of enumeration
         # so we can replace the list items in place

src/cdn_definitions/data.yaml

@@ -225,7 +225,7 @@ rhel_open_dist:
 # repo_content_sync configures selective content synchronization from RHEL repos to other products.
 # It is used e.g. by UBI to sync content to Public CDN.
 repo_content_sync:
-  stage:
+  stage: &repo_content_sync_yaml_anchor
   # Source git repo contains the configuration for tooling that facilitates
   # the repo content sync (currently ubipop).
   # The configuration includes content set labels and lists with allowed and blocked packages.
@@ -237,11 +237,7 @@ repo_content_sync:
     populate_dot_repos: False
   - source: https://example.com/client-tools/data
     populate_dot_repos: True
-  prod:
-  - source: https://example.com/ubi/data
-    populate_dot_repos: False
-  - source: https://example.com/client-tools/data
-    populate_dot_repos: True
+  prod: *repo_content_sync_yaml_anchor
 
 # repo_overrides can be used to define mappings between certain criteria matching CDN repos
 # and configuration which should be set on those repos. The intended usage is to allow