hotsos/core: add name aliasing support

at the moment, scenarios are using the long import paths in order to
reference to a Python property. this feature allows assigning an alias
to a Python class or variable in order to make using plugin property
interfaces easier.

Added aliases to the plugins.
Updated existing scenarios to use aliases.
Added unit tests for the aliasing code.
Updated the docs.

Fixes #912

Signed-off-by: Mustafa Kemal Gilor <[email protected]>

doc/source/contrib/language_ref/property_ref/main_properties.rst

@@ -18,6 +18,7 @@ Or they can reference a Python property. This is done by prefixing the import st
 
   vars:
     foo: '@path.to.myproperty'
+    bar: '@property.alias'
 
 A :ref:`factory <FactoryClasses>` reference can also be defined using the following form:
 
@@ -46,6 +47,89 @@ Variables are accessible from any property within the file in which they are def
 
 NOTE: global properties are not yet supported.
 
+Aliases
+=======
+
+Aliasing provides easier access to a class or property. The class or property needs to
+be aliased in order to use this feature.
+
+.. code-block:: python
+
+  class MyHelperClass:
+
+    @property
+    def my_awesome_property(self):
+      return True
+
+
+Normally, if the user wants to retrieve the value of the my_awesome_property in a YAML scenario
+they have to write the whole import path to the class, as follows:
+
+.. code-block:: yaml
+
+  vars:
+    foo: '@hotsos.module.path.MyHelperClass.my_awesome_property'
+  checks:
+    foo_is_true:
+      requires:
+        varops: [[$foo], [eq, true]]
+
+But, with the help of aliasing, we can make it easier to type and remember for the user:
+
+.. code-block:: python
+
+  from hotsos.core.alias import alias
+
+  @alias("helper")
+  class MyHelperClass:
+
+    @property
+    def my_awesome_property(self):
+      return True
+
+... so the previous example can be written as follows:
+
+.. code-block:: yaml
+
+  vars:
+    foo: '@helper.my_awesome_property'
+  checks:
+    foo_is_true:
+      requires:
+        varops: [[$foo], [eq, true]]
+
+Individual properties can be aliased too:
+
+.. code-block:: python
+
+  from hotsos.core.alias import alias
+
+  class MyHelperClass:
+
+    @alias('awesomeness')
+    @property
+    def my_awesome_property(self):
+      return True
+
+.. code-block:: yaml
+
+  vars:
+    awesome: '@awesomeness'
+
+
+Aliasing works for the following constructs:
+
+- Python property names
+- Class names (e.g. Config handler class type name)
+
+Alias Naming
+------------
+
+An alias can be anything. The only limitation is that an alias cannot start with the
+name of the main package (i.e., `hotsos.`). This is to prevent mixing up aliases with
+the real property paths. The alias registration will fail with `AliasForbiddenError(...)`
+in such cases.
+
 Checks
 ======
 

doc/source/contrib/language_ref/property_ref/requirement_types.rst

@@ -30,14 +30,14 @@ Usage:
 
 .. code-block:: yaml
 
-    property: <import path to python property>
+    property: <import path to python property or alias>
 
 or
 
 .. code-block:: yaml
 
     property:
-      path: <import path to python property>
+      path: <import path to python property or alias>
       ops: OPS_LIST
 
 Cache keys:
@@ -269,7 +269,7 @@ Usage:
 .. code-block:: yaml
 
     config:
-      handler: <import path>
+      handler: <import path or alias>
       path: <path to config file>
       assertions:
         - allow-unset: <bool>
@@ -295,7 +295,7 @@ Example:
     checks:
       checkcfg:
         config:
-          handler: hotsos.core.plugins.openstack.OpenstackConfig
+          handler: openstack.config
           path: etc/nova/nova.conf
           assertions:
             - key: debug

doc/source/contrib/scenarios.rst

@@ -67,7 +67,7 @@ matches and the second is a fallback:
 .. code-block:: yaml
 
     vars:
-      mem_current: '@hotsos.core.host_helpers.systemd.ServiceFactory.memory_current:neverfail'
+      mem_current: '@systemd.service.memory_current:neverfail'
     checks:
       is_enabled:
         systemd:

doc/source/contrib/writing_checks_overview.rst

@@ -50,5 +50,6 @@ the rest of the directory will only be run if it resolves to *True*:
     requires:
       or:
         - property: hotsos.core.plugins.myplugin.mustbetrue
+        - property: alias.mustbetrue
         - path: file/that/must/exist
 

hotsos/core/alias.py

@@ -0,0 +1,105 @@
+"""Aliasing utilities."""
+
+from hotsos.core.log import log
+
+
+class AliasAlreadyInUseError(Exception):
+    """Raised when an alias is already in use."""
+
+    def __init__(self, name):
+        self.message = f"Alias '{name}` already in use!"
+
+    def __str__(self):
+        return self.message
+
+
+class AliasForbiddenError(Exception):
+    """Raised when an alias is forbidden to use."""
+
+    def __init__(self, name):
+        self.message = f"Alias '{name}` is forbidden!"
+
+    def __str__(self):
+        return self.message
+
+
+class AliasRegistry:
+    """
+    A class that provides a registry for aliasing Python things.
+    """
+
+    # A class-level dictionary to store registered aliases.
+    registry = {}
+
+    @staticmethod
+    def register(name, decoratee):
+        """
+        Register a function, method, or property under an alias.
+
+        This method handles different types of Python objects and creates
+        appropriate wrappers or registrations based on the object type.
+
+        Args:
+            name (str): The alias under which to register the decoratee.
+            decoratee (callable or property): The Python object to be
+            registered.
+
+        Raises:
+            AliasAlreadyInUseError: If the alias name is already registered.
+            AliasForbiddenError: If the alias name starts with "hotsos."
+        """
+        isprop = isinstance(decoratee, property)
+        target = decoratee.fget if isprop else decoratee
+
+        if name.startswith("hotsos."):
+            raise AliasForbiddenError(name)
+
+        if name in AliasRegistry.registry:
+            log.debug("alias registration failed -- already in use(`%s`)",
+                      name)
+            raise AliasAlreadyInUseError(name)
+
+        import_path = f"{target.__module__}.{target.__qualname__}"
+        log.debug("registering alias `%s` --> {%s}", name, import_path)
+        # Register full import path.
+        AliasRegistry.registry[name] = import_path
+
+    @staticmethod
+    def resolve(the_alias, default=None):
+        """
+        Retrieve a registered alias.
+
+        Args:
+            the_alias (str): The alias to retrieve.
+
+        Returns:
+            callable: The function or wrapper associated with the alias.
+
+        Raises:
+            NoSuchAliasError: No such alias in the registry.
+        """
+
+        if the_alias not in AliasRegistry.registry:
+            log.debug(
+                "alias `%s` not found in the registry, "
+                "returning the default value",
+                the_alias,
+            )
+            return default
+
+        value = AliasRegistry.registry[the_alias]
+        log.debug("alias %s resolved to %s", the_alias, value)
+        return value
+
+
+def alias(argument):
+    """Create an alias for a property, function or a thing."""
+
+    def real_decorator(func):
+        """We're not wrapping the func as we don't want
+        to do anything at runtime. We just want to alias
+        `func` to some user-defined name and call it on-demand."""
+        AliasRegistry.register(argument, func)
+        return func
+
+    return real_decorator

hotsos/core/host_helpers/__init__.py

@@ -37,3 +37,7 @@
     AAProfileFactory,
     ApparmorHelper,
 )
+from .filestat import (  # noqa: F403,F401
+    FileFactory,
+    FileObj
+)

hotsos/core/host_helpers/apparmor.py

@@ -10,6 +10,7 @@
 )
 from hotsos.core.factory import FactoryBase
 from hotsos.core.host_helpers.cli import CLIHelperFile
+from hotsos.core.alias import alias
 
 
 @dataclass
@@ -81,6 +82,7 @@ def profiles_unconfined(self):
         return self.profiles.get('unconfined', {}).get('profiles', [])
 
 
+@alias('apparmor.profile')
 class AAProfileFactory(FactoryBase):
     """
     Dynamically create AAProfile objects using profile name.

hotsos/core/host_helpers/filestat.py

@@ -3,6 +3,7 @@
 from hotsos.core.config import HotSOSConfig
 from hotsos.core.factory import FactoryBase
 from hotsos.core.log import log
+from hotsos.core.alias import alias
 
 
 class FileObj():
@@ -38,6 +39,7 @@ def size(self):
         return size
 
 
+@alias('file')
 class FileFactory(FactoryBase):
     """
     Factory to dynamically create FileObj objects using file path as input.

hotsos/core/host_helpers/packaging.py

@@ -7,6 +7,7 @@
 from hotsos.core.host_helpers.cli import CLIHelper
 from hotsos.core.log import log
 from hotsos.core.utils import sorted_dict
+from hotsos.core.alias import alias
 
 
 class DPKGBadVersionSyntax(Exception):
@@ -484,6 +485,7 @@ class AptPackage:
     version: str
 
 
+@alias('apt.package')
 class AptFactory(FactoryBase):
     """
     Factory to dynamically get package versions.

hotsos/core/host_helpers/ssl.py

@@ -7,6 +7,7 @@
 from hotsos.core.factory import FactoryBase
 from hotsos.core.host_helpers.cli import CLIHelper
 from hotsos.core.log import log
+from hotsos.core.alias import alias
 
 
 class SSLCertificate():
@@ -65,6 +66,7 @@ def certificate_expires_soon(self):
         return self.certificate.days_to_expire <= self.expire_days
 
 
+@alias('sslcert')
 class SSLCertificatesFactory(FactoryBase):
     """
     Factory to dynamically create SSLCertificate objects for given paths.

hotsos/core/host_helpers/systemd.py

@@ -19,6 +19,7 @@
 from hotsos.core.host_helpers import CLIHelper, CLIHelperFile
 from hotsos.core.host_helpers.common import ServiceManagerBase
 from hotsos.core.log import log
+from hotsos.core.alias import alias
 
 
 class SystemdService():
@@ -354,6 +355,7 @@ def _service_filtered_ps(self):
         return ps_filtered
 
 
+@alias("systemd.service")
 class ServiceFactory(FactoryBase):
     """
     Factory to dynamically create SystemdService objects for given services.

hotsos/core/plugins/juju/common.py

@@ -3,6 +3,7 @@
 from hotsos.core.host_helpers import PebbleHelper, SystemdHelper
 from hotsos.core.plugins.juju.resources import JujuBase
 from hotsos.core import plugintools
+from hotsos.core.alias import alias
 
 SVC_VALID_SUFFIX = r'[0-9a-zA-Z-_]*'
 JUJU_SVC_EXPRS = [rf'mongod{SVC_VALID_SUFFIX}',
@@ -12,6 +13,7 @@
                   rf'(?:^|[^\s])juju-db{SVC_VALID_SUFFIX}']
 
 
+@alias('juju')
 class JujuChecks(plugintools.PluginPartBase, JujuBase):
     """ Juju checks. """
     plugin_name = 'juju'

hotsos/core/plugins/juju/resources.py

@@ -11,6 +11,7 @@
 from hotsos.core.config import HotSOSConfig
 from hotsos.core.log import log
 from hotsos.core import utils
+from hotsos.core.alias import alias
 
 
 class JujuMachine():
@@ -176,6 +177,7 @@ class JujuCharm:
     version: int
 
 
+@alias('juju.base')
 class JujuBase():
     """ Juju checks base class. """
     CHARM_MANIFEST_GLOB = "agents/unit-*/state/deployer/manifests"
@@ -259,6 +261,7 @@ def charm_names(self):
         return list(self.charms.keys())
 
 
+@alias('juju.bin')
 class JujuBinaryInterface(JujuBase):
     """ Interface to juju binary. """
     @property

hotsos/core/plugins/kernel/common.py

@@ -5,8 +5,10 @@
 from hotsos.core import host_helpers, plugintools
 from hotsos.core.config import HotSOSConfig
 from hotsos.core.plugins.kernel.config import KernelConfig
+from hotsos.core.alias import alias
 
 
+@alias('kernel')
 class KernelBase():
     """ Base class for kernel plugin helpers. """
     @cached_property