partitions: add feature and validation (#489)

Signed-off-by: Callahan Kovacs <[email protected]>

craft_parts/errors.py

@@ -49,8 +49,8 @@ def __str__(self) -> str:
         return "\n".join(components)
 
 
-class FeatureDisabled(PartsError):
-    """The requested feature is not enabled."""
+class FeatureError(PartsError):
+    """A feature is not configured as expected."""
 
     def __init__(self, message: str) -> None:
         self.message = message

craft_parts/features.py

@@ -27,9 +27,14 @@
 
 @dataclasses.dataclass(frozen=True)
 class Features(metaclass=Singleton):
-    """Configurable craft-parts features."""
+    """Configurable craft-parts features.
+
+    :cvar enable_overlay: Enables the overlay step.
+    :cvar enable_partitions: Enables the usage of partitions.
+    """
 
     enable_overlay: bool = False
+    enable_partitions: bool = False
 
     @classmethod
     def reset(cls) -> None:

craft_parts/infos.py

@@ -46,6 +46,7 @@ class ProjectVar(YamlModel):
     updated: bool = False
 
 
+# pylint: disable-next=too-many-instance-attributes
 class ProjectInfo:
     """Project-level information containing project-specific fields.
 
@@ -67,6 +68,7 @@ class ProjectInfo:
     :param project_vars: A dictionary containing the project variables.
     :param custom_args: Any additional arguments defined by the application
         when creating a :class:`LifecycleManager`.
+    :param partitions: A list of partitions.
     """
 
     def __init__(
@@ -82,6 +84,7 @@ def __init__(
         project_name: Optional[str] = None,
         project_vars_part_name: Optional[str] = None,
         project_vars: Optional[Dict[str, str]] = None,
+        partitions: Optional[List[str]] = None,
         **custom_args: Any,  # custom passthrough args
     ):
         if not project_dirs:
@@ -99,6 +102,7 @@ def __init__(
         self._project_name = project_name
         self._project_vars_part_name = project_vars_part_name
         self._project_vars = {k: ProjectVar(value=v) for k, v in pvars.items()}
+        self._partitions = partitions
         self._custom_args = custom_args
         self.global_environment: Dict[str, str] = {}
 
@@ -184,6 +188,11 @@ def project_options(self) -> Dict[str, Any]:
             "project_vars": self._project_vars,
         }
 
+    @property
+    def partitions(self) -> Optional[List[str]]:
+        """Return the project's partitions."""
+        return self._partitions
+
     def set_project_var(
         self,
         name: str,

craft_parts/lifecycle_manager.py

@@ -74,6 +74,9 @@ class LifecycleManager:
     :param project_vars_part_name: Project variables can only be set in the part
         matching this name.
     :param project_vars: A dictionary containing project variables.
+    :param partitions: A list of partitions to use when the partitions feature is
+        enabled. The first partition must be "default" and all partitions must be
+        lowercase alphabetical.
     :param custom_args: Any additional arguments that will be passed directly
         to :ref:`callbacks<callbacks>`.
     """
@@ -99,6 +102,7 @@ def __init__(
         base_layer_hash: Optional[bytes] = None,
         project_vars_part_name: Optional[str] = None,
         project_vars: Optional[Dict[str, str]] = None,
+        partitions: Optional[List[str]] = None,
         **custom_args: Any,  # custom passthrough args
     ):
         # pylint: disable=too-many-locals
@@ -115,6 +119,8 @@ def __init__(
         if "parts" not in all_parts:
             raise ValueError("parts definition is missing")
 
+        _validate_partitions(partitions)
+
         packages.Repository.configure(application_package_name)
 
         project_dirs = ProjectDirs(work_dir=work_dir)
@@ -130,6 +136,7 @@ def __init__(
             project_dirs=project_dirs,
             project_vars_part_name=project_vars_part_name,
             project_vars=project_vars,
+            partitions=partitions,
             **custom_args,
         )
 
@@ -263,7 +270,7 @@ def get_primed_stage_packages(self, *, part_name: str) -> Optional[List[str]]:
 def _ensure_overlay_supported() -> None:
     """Overlay is only supported in Linux and requires superuser privileges."""
     if not Features().enable_overlay:
-        raise errors.FeatureDisabled("Overlays are not supported.")
+        raise errors.FeatureError("Overlays are not supported.")
 
     if sys.platform != "linux":
         raise errors.OverlayPlatformError()
@@ -324,3 +331,38 @@ def _build_part(
     )
 
     return part
+
+
+def _validate_partitions(partitions: Optional[List[str]]) -> None:
+    """Validate the partition feature set.
+
+    If the partition feature is enabled, then:
+      - the first partition must be "default"
+      - each partition must contain only lowercase alphabetical characters
+      - partitions are unique
+
+    :param partitions: Partition data to verify.
+
+    :raises ValueError: If the partitions are not valid or the feature is not enabled.
+    """
+    if Features().enable_partitions:
+        if not partitions:
+            raise errors.FeatureError(
+                "Partition feature is enabled but no partitions are defined."
+            )
+
+        if partitions[0] != "default":
+            raise ValueError("First partition must be 'default'.")
+
+        if any(not re.fullmatch("[a-z]+", partition) for partition in partitions):
+            raise ValueError(
+                "Partitions must only contain lowercase alphabetical characters."
+            )
+
+        if len(partitions) != len(set(partitions)):
+            raise ValueError("Partitions must be unique.")
+
+    elif partitions:
+        raise errors.FeatureError(
+            "Partitions are defined but partition feature is not enabled."
+        )

craft_parts/sequencer.py

@@ -81,7 +81,7 @@ def plan(
         :returns: The list of actions that should be executed.
         """
         if target_step == Step.OVERLAY and not Features().enable_overlay:
-            raise errors.FeatureDisabled("Overlay step is not supported.")
+            raise errors.FeatureError("Overlay step is not supported.")
 
         self._actions = []
         self._add_all_actions(target_step, part_names)

setup.py

@@ -86,12 +86,14 @@ def is_rtd() -> bool:
     "codespell",
     "coverage",
     "isort",
+    "hypothesis",
     "pydocstyle",
     "pylint",
     "pylint-fixme-info",
     "pylint-pytest",
     "pyright",
     "pytest",
+    "pytest-check",
     "pytest-cov",
     "pytest-mock",
     "requests-mock",

tests/conftest.py

@@ -71,6 +71,17 @@ def enable_overlay_feature():
     Features.reset()
 
 
+@pytest.fixture
+def enable_partitions_feature():
+    assert Features().enable_partitions is False
+    Features.reset()
+    Features(enable_partitions=True)
+
+    yield
+
+    Features.reset()
+
+
 @pytest.fixture(autouse=True)
 def temp_xdg(tmpdir, mocker):
     """Use a temporary locaction for XDG directories."""