hotsos/core: add name aliasing support

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
 
 lower_bound_ops = ["gt", "ge", "eq"]  # ops that define a lower bound
 upper_bound_ops = ["lt", "le", "eq"]  # ops that define an upper bound
@@ -495,6 +496,7 @@ 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():
@@ -357,6 +358,7 @@ 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