Use custom WorkflowFactory to provide plugin install instructions

The `WorkflowFactory` from `aiida-core` is replaced with a custom
version in the `aiida_common_workflows.plugins.factories` module. This
function will call the factory from `aiida-core` but catch the
`MissingEntryPointError` exception. In this case, if the entry point
corresponds to a plugin implementation of one of the common workflows
the exception is reraised but with a useful message that provides the
user with the install command to install the necessary plugin package.

While this should catch all cases of users trying to load a workflow for
a plugin that is not installed through its entry point, it won't catch
import errors that are raised when a module is imported directly from
that plugin package. Therefore, these imports should not be placed at
the top of modules, but placed inside functions/methods of the
implementation as much as possible.

src/aiida_common_workflows/plugins/__init__.py

@@ -1,4 +1,10 @@
 """Module with utilities for working with the plugins provided by this plugin package."""
 from .entry_point import get_entry_point_name_from_class, get_workflow_entry_point_names, load_workflow_entry_point
+from .factories import WorkflowFactory
 
-__all__ = ('get_workflow_entry_point_names', 'get_entry_point_name_from_class', 'load_workflow_entry_point')
+__all__ = (
+    'WorkflowFactory',
+    'get_workflow_entry_point_names',
+    'get_entry_point_name_from_class',
+    'load_workflow_entry_point',
+)

src/aiida_common_workflows/plugins/entry_point.py

@@ -3,6 +3,8 @@
 
 from aiida.plugins import entry_point
 
+from .factories import WorkflowFactory
+
 PACKAGE_PREFIX = 'common_workflows'
 
 __all__ = ('get_workflow_entry_point_names', 'get_entry_point_name_from_class', 'load_workflow_entry_point')
@@ -38,5 +40,5 @@ def load_workflow_entry_point(workflow: str, plugin_name: str):
     :param plugin_name: name of the plugin implementation.
     :return: the workchain class of the plugin implementation of the common workflow.
     """
-    prefix = f'{PACKAGE_PREFIX}.{workflow}.{plugin_name}'
-    return entry_point.load_entry_point('aiida.workflows', prefix)
+    entry_point_name = f'{PACKAGE_PREFIX}.{workflow}.{plugin_name}'
+    return WorkflowFactory(entry_point_name)

src/aiida_common_workflows/plugins/factories.py

@@ -0,0 +1,47 @@
+"""Factories to load entry points."""
+import typing as t
+
+from aiida import plugins
+from aiida.common import exceptions
+
+if t.TYPE_CHECKING:
+    from aiida.engine import WorkChain
+    from importlib_metadata import EntryPoint
+
+__all__ = ('WorkflowFactory',)
+
+
+@t.overload
+def WorkflowFactory(entry_point_name: str, load: t.Literal[True] = True) -> t.Union[t.Type['WorkChain'], t.Callable]:
+    ...
+
+
+@t.overload
+def WorkflowFactory(entry_point_name: str, load: t.Literal[False]) -> 'EntryPoint':
+    ...
+
+
+def WorkflowFactory(entry_point_name: str, load: bool = True) -> t.Union['EntryPoint', t.Type['WorkChain'], t.Callable]:  # noqa: N802
+    """Return the `WorkChain` sub class registered under the given entry point.
+
+    :param entry_point_name: the entry point name.
+    :param load: if True, load the matched entry point and return the loaded resource instead of the entry point itself.
+    :return: sub class of :py:class:`~aiida.engine.processes.workchains.workchain.WorkChain` or a `workfunction`
+    :raises aiida.common.MissingEntryPointError: entry point was not registered
+    :raises aiida.common.MultipleEntryPointError: entry point could not be uniquely resolved
+    :raises aiida.common.LoadingEntryPointError: entry point could not be loaded
+    :raises aiida.common.InvalidEntryPointTypeError: if the type of the loaded entry point is invalid.
+    """
+    common_workflow_prefixes = ('common_workflows.relax.', 'common_workflows.bands.')
+    try:
+        return plugins.WorkflowFactory(entry_point_name, load)
+    except exceptions.MissingEntryPointError as exception:
+        for prefix in common_workflow_prefixes:
+            if entry_point_name.startswith(prefix):
+                plugin_name = entry_point_name.removeprefix(prefix)
+                raise exceptions.MissingEntryPointError(
+                    f'Could not load the entry point `{entry_point_name}`, probably because the plugin package is not '
+                    f'installed. Please install it with `pip install aiida-common-workflows[{plugin_name}]`.'
+                ) from exception
+        else:  # noqa: PLW0120
+            raise

src/aiida_common_workflows/workflows/relax/abinit/workchain.py

@@ -3,7 +3,7 @@
 from aiida import orm
 from aiida.common import exceptions
 from aiida.engine import calcfunction
-from aiida_abinit.workflows.base import AbinitBaseWorkChain
+from aiida.plugins import WorkflowFactory
 
 from ..workchain import CommonRelaxWorkChain
 from .generator import AbinitCommonRelaxInputGenerator
@@ -44,7 +44,7 @@ def get_total_magnetization(parameters):
 class AbinitCommonRelaxWorkChain(CommonRelaxWorkChain):
     """Implementation of `aiida_common_workflows.common.relax.workchain.CommonRelaxWorkChain` for Abinit."""
 
-    _process_class = AbinitBaseWorkChain
+    _process_class = WorkflowFactory('abinit.base')
     _generator_class = AbinitCommonRelaxInputGenerator
 
     def convert_outputs(self):

src/aiida_common_workflows/workflows/relax/castep/generator.py

@@ -8,14 +8,15 @@
 import yaml
 from aiida import engine, orm, plugins
 from aiida.common import exceptions
-from aiida_castep.data import get_pseudos_from_structure
-from aiida_castep.data.otfg import OTFGGroup
 
 from aiida_common_workflows.common import ElectronicType, RelaxType, SpinType
 from aiida_common_workflows.generators import ChoiceType, CodeType
 
 from ..generator import CommonRelaxInputGenerator
 
+if t.TYPE_CHECKING:
+    from aiida_castep.data.otfg import OTFGGroup
+
 KNOWN_BUILTIN_FAMILIES = ('C19', 'NCP19', 'QC5', 'C17', 'C9')
 
 __all__ = ('CastepCommonRelaxInputGenerator',)
@@ -247,8 +248,8 @@ def generate_inputs(
     :param override: a dictionary to override specific inputs
     :return: input dictionary
     """
-
     from aiida.common.lang import type_check
+    from aiida_castep.data.otfg import OTFGGroup
 
     family_name = protocol['relax']['base']['pseudos_family']
     if isinstance(family_name, orm.Str):
@@ -285,7 +286,7 @@ def generate_inputs_relax(
     protocol: t.Dict,
     code: orm.Code,
     structure: orm.StructureData,
-    otfg_family: OTFGGroup,
+    otfg_family: 'OTFGGroup',
     override: t.Optional[t.Dict[str, t.Any]] = None,
 ) -> t.Dict[str, t.Any]:
     """Generate the inputs for the `CastepCommonRelaxWorkChain` for a given code, structure and pseudo potential family.
@@ -321,7 +322,7 @@ def generate_inputs_base(
     protocol: t.Dict,
     code: orm.Code,
     structure: orm.StructureData,
-    otfg_family: OTFGGroup,
+    otfg_family: 'OTFGGroup',
     override: t.Optional[t.Dict[str, t.Any]] = None,
 ) -> t.Dict[str, t.Any]:
     """Generate the inputs for the `CastepBaseWorkChain` for a given code, structure and pseudo potential family.
@@ -359,7 +360,7 @@ def generate_inputs_calculation(
     protocol: t.Dict,
     code: orm.Code,
     structure: orm.StructureData,
-    otfg_family: OTFGGroup,
+    otfg_family: 'OTFGGroup',
     override: t.Optional[t.Dict[str, t.Any]] = None,
 ) -> t.Dict[str, t.Any]:
     """Generate the inputs for the `CastepCalculation` for a given code, structure and pseudo potential family.
@@ -372,6 +373,7 @@ def generate_inputs_calculation(
     :return: the fully defined input dictionary.
     """
     from aiida_castep.calculations.helper import CastepHelper
+    from aiida_castep.data import get_pseudos_from_structure
 
     override = {} if not override else override.get('calc', {})
     # This merge perserves the merged `parameters` in the override
@@ -415,9 +417,8 @@ def ensure_otfg_family(family_name, force_update=False):
     NOTE: CASTEP also supports UPF families, but it is not enabled here, since no UPS based protocol
     has been implemented.
     """
-
     from aiida.common import NotExistent
-    from aiida_castep.data.otfg import upload_otfg_family
+    from aiida_castep.data.otfg import OTFGGroup, upload_otfg_family
 
     # Ensure family name is a str
     if isinstance(family_name, orm.Str):

src/aiida_common_workflows/workflows/relax/quantum_espresso/generator.py

@@ -3,7 +3,6 @@
 
 import yaml
 from aiida import engine, orm, plugins
-from aiida_quantumespresso.workflows.protocols.utils import recursive_merge
 
 from aiida_common_workflows.common import ElectronicType, RelaxType, SpinType
 from aiida_common_workflows.generators import ChoiceType, CodeType
@@ -108,8 +107,8 @@ def _construct_builder(self, **kwargs) -> engine.ProcessBuilder:  # noqa: PLR091
 
         The keyword arguments will have been validated against the input generator specification.
         """
-
         from aiida_quantumespresso.common import types
+        from aiida_quantumespresso.workflows.protocols.utils import recursive_merge
         from qe_tools import CONSTANTS
 
         structure = kwargs['structure']

tests/test_minimal_install.py

@@ -4,6 +4,8 @@
 installed. This guarantees that most of the code can be imported without any plugin packages being installed.
 """
 import pytest
+from aiida.common import exceptions
+from aiida_common_workflows.plugins import WorkflowFactory, get_workflow_entry_point_names
 
 
 @pytest.mark.minimal_install
@@ -18,3 +20,29 @@ def test_imports():
     import aiida_common_workflows.workflows
     import aiida_common_workflows.workflows.dissociation
     import aiida_common_workflows.workflows.eos  # noqa: F401
+
+
+@pytest.mark.minimal_install
+@pytest.mark.parametrize('entry_point_name', get_workflow_entry_point_names('relax'))
+def test_workflow_factory_relax(entry_point_name):
+    """Test that trying to load common relax workflow implementations will raise if not installed.
+
+    The exception message should provide the pip command to install the require plugin package.
+    """
+    plugin_name = entry_point_name.removeprefix('common_workflows.relax.')
+    match = rf'.*plugin package is not installed.*`pip install aiida-common-workflows\[{plugin_name}\]`.*'
+    with pytest.raises(exceptions.MissingEntryPointError, match=match):
+        WorkflowFactory(entry_point_name)
+
+
+@pytest.mark.minimal_install
+@pytest.mark.parametrize('entry_point_name', get_workflow_entry_point_names('bands'))
+def test_workflow_factory_bands(entry_point_name):
+    """Test that trying to load common bands workflow implementations will raise if not installed.
+
+    The exception message should provide the pip command to install the require plugin package.
+    """
+    plugin_name = entry_point_name.removeprefix('common_workflows.bands.')
+    match = rf'.*plugin package is not installed.*`pip install aiida-common-workflows\[{plugin_name}\]`.*'
+    with pytest.raises(exceptions.MissingEntryPointError, match=match):
+        WorkflowFactory(entry_point_name)