feat: mediate creation of gadget.yaml and kernel.yaml

snapcraft/parts/setup_assets.py

@@ -32,6 +32,13 @@
 from .desktop_file import DesktopFile
 
 
+def _uses_legacy_system_metadata(project: models.Project) -> bool:
+    """Return whether gadget/kernel metadata should follow the core22 path."""
+    return project.base == "core22" or (
+        project.base is None and project.build_base == "core22"
+    )
+
+
 def setup_assets(
     project: models.Project,
     *,
@@ -67,16 +74,16 @@ def setup_assets(
             )
             setup_hooks(component.hooks, prime_dirs[component_name])
 
-    if project.type == const.ProjectType.GADGET:
-        gadget_yaml = project_dir / "gadget.yaml"
-        if not gadget_yaml.exists():
-            raise errors.SnapcraftError("gadget.yaml is required for gadget snaps")
-        _copy_file(gadget_yaml, meta_dir / "gadget.yaml")
-
-    if project.type == const.ProjectType.KERNEL:
-        kernel_yaml = project_dir / "kernel.yaml"
-        if kernel_yaml.exists():
-            _copy_file(kernel_yaml, meta_dir / "kernel.yaml")
+    if _uses_legacy_system_metadata(project):
+        if project.type == const.ProjectType.GADGET:
+            gadget_yaml = project_dir / "gadget.yaml"
+            if not gadget_yaml.exists():
+                raise errors.SnapcraftError("gadget.yaml is required for gadget snaps")
+            _copy_file(gadget_yaml, meta_dir / "gadget.yaml")
+        elif project.type == const.ProjectType.KERNEL:
+            kernel_yaml = project_dir / "kernel.yaml"
+            if kernel_yaml.exists():
+                _copy_file(kernel_yaml, meta_dir / "kernel.yaml")
 
     icon_path = _finalize_icon(
         project.icon, assets_dir=assets_dir, gui_dir=gui_dir, prime_dir=prime_dir

snapcraft/services/package.py

@@ -29,7 +29,7 @@
 from craft_cli import emit
 from typing_extensions import override
 
-from snapcraft import errors, linters, models, pack
+from snapcraft import const, errors, linters, models, pack
 from snapcraft.errors import SnapcraftPrecreationEscapesPrimeError
 from snapcraft.linters import LinterStatus
 from snapcraft.meta import component_yaml, snap_yaml
@@ -68,6 +68,40 @@ def _get_component_yaml(self, partition: str | None = None) -> str:
         component_name = partition.removeprefix("component/")
         return component_yaml.get_str(self._project, component_name)
 
+    @package_file("meta/gadget.yaml", partition_re="default")
+    def _get_gadget_yaml(
+        self, partition: str | None = None  # noqa: ARG002
+    ) -> str | Literal[False] | None:
+        """Generate mediated gadget metadata for core24+ gadget snaps.
+
+        Returns ``False`` (leave existing file untouched) when this project
+        should not be mediated (core22 snaps use the legacy copy path in
+        ``setup_assets``) or when the project is not a gadget snap.
+        """
+        if self._project.type != const.ProjectType.GADGET:
+            return False
+
+        return self._read_project_metadata_file(
+            "gadget.yaml",
+            required=True,
+            error_message="gadget.yaml is required for gadget snaps",
+        )
+
+    @package_file("meta/kernel.yaml", partition_re="default")
+    def _get_kernel_yaml(
+        self, partition: str | None = None  # noqa: ARG002
+    ) -> str | Literal[False] | None:
+        """Generate mediated kernel metadata for core24+ kernel snaps.
+
+        Returns ``False`` (leave existing file untouched) when this project
+        should not be mediated (core22 snaps use the legacy copy path in
+        ``setup_assets``) or when the project is not a kernel snap.
+        """
+        if self._project.type != const.ProjectType.KERNEL:
+            return False
+
+        return self._read_project_metadata_file("kernel.yaml")
+
     @override
     def setup(self) -> None:
         """Application-specific service setup."""
@@ -433,6 +467,37 @@ def _get_assets_dir(self) -> pathlib.Path:
         # This is for backwards compatibility with setup_assets(...)
         return project_dir / "snap"
 
+    def _read_project_metadata_file(
+        self,
+        filename: str,
+        *,
+        required: bool = False,
+        error_message: str | None = None,
+    ) -> str | None:
+        """Read a top-level project metadata file if it exists."""
+        metadata_path = self._services.lifecycle.project_info.project_dir / filename
+        if metadata_path.exists():
+            return metadata_path.read_text(encoding="utf-8")
+
+        if required:
+            raise errors.SnapcraftError(error_message or f"{filename} is required")
+
+        return None
+
+    def _write_system_metadata(self, path: pathlib.Path) -> None:
+        """Materialize mediated gadget/kernel metadata files for core24+ snaps."""
+        meta_dir = path / "meta"
+
+        if self._project.type == const.ProjectType.GADGET:
+            contents = self._get_gadget_yaml()
+            if isinstance(contents, str):
+                (meta_dir / "gadget.yaml").write_text(contents, encoding="utf-8")
+
+        if self._project.type == const.ProjectType.KERNEL:
+            contents = self._get_kernel_yaml()
+            if isinstance(contents, str):
+                (meta_dir / "kernel.yaml").write_text(contents, encoding="utf-8")
+
     @override
     def write_metadata(self, path: pathlib.Path) -> None:
         """Write the project metadata to metadata.yaml in the given directory.
@@ -466,6 +531,7 @@ def write_metadata(self, path: pathlib.Path) -> None:
             prime_dirs=lifecycle_service.prime_dirs,
             meta_directory_handler=meta_directory_handler,
         )
+        self._write_system_metadata(path)
 
         for component in self._project.get_component_names():
             component_yaml.write(

tests/unit/parts/test_setup_assets.py

@@ -111,6 +111,30 @@ def test_gadget(yaml_data, gadget_yaml_file, new_dir):
     assert gadget_path.is_file()
 
 
+def test_gadget_core24_not_copied(yaml_data, gadget_yaml_file, new_dir):
+    project = models.Project.unmarshal(
+        yaml_data(
+            {
+                "type": "gadget",
+                "base": "core24",
+                "build-base": "core24",
+                "version": "1.0",
+                "summary": "summary",
+                "description": "description",
+            }
+        )
+    )
+
+    setup_assets(
+        project,
+        assets_dir=Path("snap"),
+        project_dir=Path.cwd(),
+        prime_dirs={None: Path("prime")},
+    )
+
+    assert not Path("prime/meta/gadget.yaml").exists()
+
+
 def test_gadget_missing(yaml_data, new_dir):
     project = models.Project.unmarshal(
         yaml_data(
@@ -144,7 +168,7 @@ def test_kernel(yaml_data, kernel_yaml_file, new_dir):
             "summary": "summary",
             "description": "description",
             "parts": {},
-            "build-base": "devel",
+            "build-base": "core22",
         }
     )
 
@@ -160,6 +184,30 @@ def test_kernel(yaml_data, kernel_yaml_file, new_dir):
     assert kernel_path.is_file()
 
 
+def test_kernel_core24_not_copied(yaml_data, kernel_yaml_file, new_dir):
+    project = models.Project.unmarshal(
+        {
+            "name": "custom-kernel",
+            "type": "kernel",
+            "confinement": "strict",
+            "version": "1.0",
+            "summary": "summary",
+            "description": "description",
+            "parts": {},
+            "build-base": "core24",
+        }
+    )
+
+    setup_assets(
+        project,
+        assets_dir=Path("snap"),
+        project_dir=Path.cwd(),
+        prime_dirs={None: Path("prime")},
+    )
+
+    assert not Path("prime/meta/kernel.yaml").exists()
+
+
 def test_kernel_missing(yaml_data, new_dir):
     project = models.Project.unmarshal(
         {
@@ -170,7 +218,7 @@ def test_kernel_missing(yaml_data, new_dir):
             "summary": "summary",
             "description": "description",
             "parts": {},
-            "build-base": "devel",
+            "build-base": "core22",
         }
     )