support unified charmcraft model

scenario/state.py

@@ -947,6 +947,8 @@ class _CharmSpec(_DCBase):
     """Charm spec."""
 
     charm_type: Type["CharmType"]
+
+    # TODO: consider unifying the data model since nowadays it's all in one file
     meta: Optional[Dict[str, Any]]
     actions: Optional[Dict[str, Any]] = None
     config: Optional[Dict[str, Any]] = None
@@ -956,16 +958,10 @@ class _CharmSpec(_DCBase):
     is_autoloaded: bool = False
 
     @staticmethod
-    def autoload(charm_type: Type["CharmType"]):
-        charm_source_path = Path(inspect.getfile(charm_type))
-        charm_root = charm_source_path.parent.parent
-
+    def _load_metadata_legacy(charm_root: Path):
+        # back in the days, we used to have separate metadata.yaml, config.yaml and actions.yaml
+        # files for charm metadata.
         metadata_path = charm_root / "metadata.yaml"
-        if not metadata_path.exists():
-            raise MetadataNotFoundError(
-                f"invalid charm root {charm_root!r}; "
-                f"expected to contain at least a `metadata.yaml` file.",
-            )
         meta = yaml.safe_load(metadata_path.open())
 
         actions = config = None
@@ -978,6 +974,35 @@ def autoload(charm_type: Type["CharmType"]):
         if actions_path.exists():
             actions = yaml.safe_load(actions_path.open())
 
+        return meta, config, actions
+
+    @staticmethod
+    def _load_metadata(charm_root: Path):
+        metadata_path = charm_root / "charmcraft.yaml"
+        meta = yaml.safe_load(metadata_path.open()) if metadata_path.exists() else {}
+        config = meta.get("config", None)
+        actions = meta.get("actions", None)
+        return meta, config, actions
+
+    @staticmethod
+    def autoload(charm_type: Type["CharmType"]):
+        charm_source_path = Path(inspect.getfile(charm_type))
+        charm_root = charm_source_path.parent.parent
+
+        metadata_path = charm_root / "metadata.yaml"
+
+        if metadata_path.exists():
+            meta, config, actions = _CharmSpec._load_metadata_legacy(charm_root)
+        else:
+            meta, config, actions = _CharmSpec._load_metadata(charm_root)
+
+        if not meta:
+            raise MetadataNotFoundError(
+                f"invalid charm root {charm_root!r}; "
+                f"expected to contain at least a `charmcraft.yaml` file "
+                f"(or a `metadata.yaml` file if it's an old charm).",
+            )
+
         return _CharmSpec(
             charm_type=charm_type,
             meta=meta,

tests/test_charm_spec_autoload.py

@@ -38,51 +38,69 @@ def create_tempcharm(
     actions=None,
     config=None,
     name: str = "MyCharm",
+    legacy: bool = True,
 ):
     src = root / "src"
     src.mkdir(parents=True)
     charmpy = src / "charm.py"
     charmpy.write_text(charm)
 
-    if meta is not None:
-        (root / "metadata.yaml").write_text(yaml.safe_dump(meta))
+    if legacy:
+        if meta is not None:
+            (root / "metadata.yaml").write_text(yaml.safe_dump(meta))
 
-    if actions is not None:
-        (root / "actions.yaml").write_text(yaml.safe_dump(actions))
+        if actions is not None:
+            (root / "actions.yaml").write_text(yaml.safe_dump(actions))
 
-    if config is not None:
-        (root / "config.yaml").write_text(yaml.safe_dump(config))
+        if config is not None:
+            (root / "config.yaml").write_text(yaml.safe_dump(config))
+    else:
+        unified_meta = meta or {}
+        if actions:
+            unified_meta["actions"] = actions
+        if config:
+            unified_meta["config"] = config
+        if unified_meta:
+            (root / "charmcraft.yaml").write_text(yaml.safe_dump(unified_meta))
 
     with import_name(name, charmpy) as charm:
         yield charm
 
 
-def test_meta_autoload(tmp_path):
-    with create_tempcharm(tmp_path, meta={"name": "foo"}) as charm:
+@pytest.mark.parametrize("legacy", (True, False))
+def test_meta_autoload(tmp_path, legacy):
+    with create_tempcharm(tmp_path, legacy=legacy, meta={"name": "foo"}) as charm:
         ctx = Context(charm)
         ctx.run("start", State())
 
 
-def test_no_meta_raises(tmp_path):
+@pytest.mark.parametrize("legacy", (True, False))
+def test_no_meta_raises(tmp_path, legacy):
     with create_tempcharm(
         tmp_path,
+        legacy=legacy,
     ) as charm:
         # metadata not found:
         with pytest.raises(ContextSetupError):
             Context(charm)
 
 
-def test_relations_ok(tmp_path):
+@pytest.mark.parametrize("legacy", (True, False))
+def test_relations_ok(tmp_path, legacy):
     with create_tempcharm(
-        tmp_path, meta={"name": "josh", "requires": {"cuddles": {"interface": "arms"}}}
+        tmp_path,
+        legacy=legacy,
+        meta={"name": "josh", "requires": {"cuddles": {"interface": "arms"}}},
     ) as charm:
         # this would fail if there were no 'cuddles' relation defined in meta
         Context(charm).run("start", State(relations=[Relation("cuddles")]))
 
 
-def test_config_defaults(tmp_path):
+@pytest.mark.parametrize("legacy", (True, False))
+def test_config_defaults(tmp_path, legacy):
     with create_tempcharm(
         tmp_path,
+        legacy=legacy,
         meta={"name": "josh"},
         config={"options": {"foo": {"type": "bool", "default": True}}},
     ) as charm: