add support to override refspec of repos

This patch adds the top-level `overrides` entry, which is used to
override (or pin) the refspec of repositories. The main difference to a
direct override is that this logic only applies to repos that are
already defined. By that, a superset of all repos can be added to this
entry (similar to a global lockfile), but only the currently active ones
are affected. A new top-level keyword is required because everything
below the "repos" keyword is potentially defined by "default" values.
For the locking mechanism, a clear separation between overrides (only
override if existing) and definitions is required to be able to define a
global lockfile with all possible repos, while just defining some repos.

Proposed-by: Ross Burton <ross@burtonini.com>
Signed-off-by: Felix Moessbauer <felix.moessbauer@siemens.com>
[Jan: also bump __file_version__]
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>

kas/__version__.py

@@ -28,5 +28,5 @@ __copyright__ = 'Copyright (c) Siemens AG, 2017-2020'
 __version__ = '3.2.3'
 
 # Please update docs/format-changelog.rst when changing the file version.
-__file_version__ = 13
+__file_version__ = 14
 __compatible_file_version__ = 1

kas/config.py

@@ -104,11 +104,14 @@ class Config:
             `name`.
         """
         repo_defaults = self._config.get('defaults', {}).get('repos', {})
+        overrides = self._config.get('overrides', {}) \
+                                .get('repos', {}).get(name, {})
         config = self.get_repos_config()[name] or {}
         return Repo.factory(name,
                             config,
                             repo_defaults,
-                            self.top_repo_path)
+                            self.top_repo_path,
+                            overrides)
 
     def _get_repo_dict(self):
         """

kas/repos.py

@@ -90,7 +90,8 @@ class Repo:
                                 self.path, self._layers)
 
     @staticmethod
-    def factory(name, repo_config, repo_defaults, repo_fallback_path):
+    def factory(name, repo_config, repo_defaults, repo_fallback_path,
+                repo_overrides={}):
         """
             Returns a Repo instance depending on params.
         """
@@ -119,8 +120,8 @@ class Repo:
         url = repo_config.get('url', None)
         name = repo_config.get('name', name)
         typ = repo_config.get('type', 'git')
-        refspec = repo_config.get('refspec',
-                                  repo_defaults.get('refspec', None))
+        refspec = repo_overrides.get('refspec', repo_config.get('refspec',
+                                     repo_defaults.get('refspec', None)))
         if refspec is None and url is not None:
             logging.error('No refspec specified for repository "%s". This is '
                           'only allowed for local repositories.', name)

kas/schema-kas.json

@@ -89,6 +89,24 @@
                 }
             }
         },
+        "overrides": {
+            "type": "object",
+            "additionalProperties": false,
+            "properties": {
+                "repos": {
+                    "type": "object",
+                    "additionalProperties": {
+                        "type": "object",
+                        "additionalProperties": false,
+                        "properties": {
+                            "refspec" : {
+                                "type": "string"
+                            }
+                        }
+                    }
+                }
+            }
+        },
         "machine": {
             "type": "string"
         },