Process: Have inputs property always return AttributesFrozenDict (

#6010)

The `Process.inputs` property as implemented in `plumpy` has as a return
type `AttributesFrozenDict | None`. This leads to a lot unnecessary
complexities in the code having to deal with the potential `None`, where
really this should never really occur. A lot of user code will never
even check for `Process.inputs` returning `None`, such as in `WorkChain`
implementations, and as a result type checkers will fail forcing a user
to either unnecessarily complicate their code by explicitly checking for
`None`, but will typically end up silencing the error.

The `inputs` property is overridden here to return an empty
`AttributesFrozenDict` in case the inputs are `None`, which allows to
simplify the return type and get rid of any type errors in downstream
code.

aiida/engine/processes/calcjobs/calcjob.py

@@ -539,11 +539,11 @@ def run(self) -> Union[plumpy.process_states.Stop, int, plumpy.process_states.Wa
             `Wait` command if the calcjob is to be uploaded
 
         """
-        if self.inputs.metadata.dry_run:  # type: ignore[union-attr]
+        if self.inputs.metadata.dry_run:
             self._perform_dry_run()
             return plumpy.process_states.Stop(None, True)
 
-        if 'remote_folder' in self.inputs:  # type: ignore[operator]
+        if 'remote_folder' in self.inputs:
             exit_code = self._perform_import()
             return exit_code
 
@@ -596,7 +596,7 @@ def _setup_inputs(self) -> None:
         # will have an associated computer, but in that case the ``computer`` property should return ``None`` and
         # nothing would change anyway.
         if not self.node.computer:
-            self.node.computer = self.inputs.code.computer  # type: ignore[union-attr]
+            self.node.computer = self.inputs.code.computer
 
     def _perform_dry_run(self):
         """Perform a dry run.
@@ -640,9 +640,7 @@ def _perform_import(self):
             with SandboxFolder(filepath_sandbox) as folder:
                 with SandboxFolder(filepath_sandbox) as retrieved_temporary_folder:
                     self.presubmit(folder)
-                    self.node.set_remote_workdir(
-                        self.inputs.remote_folder.get_remote_path()  # type: ignore[union-attr]
-                    )
+                    self.node.set_remote_workdir(self.inputs.remote_folder.get_remote_path())
                     retrieve_calculation(self.node, transport, retrieved_temporary_folder.abspath)
                     self.node.set_state(CalcJobState.PARSING)
                     self.node.base.attributes.set(orm.CalcJobNode.IMMIGRATED_KEY, True)
@@ -821,7 +819,7 @@ def presubmit(self, folder: Folder) -> CalcInfo:
 
         inputs = self.node.base.links.get_incoming(link_type=LinkType.INPUT_CALC)
 
-        if not self.inputs.metadata.dry_run and not self.node.is_stored:  # type: ignore[union-attr]
+        if not self.inputs.metadata.dry_run and not self.node.is_stored:
             raise InvalidOperation('calculation node is not stored.')
 
         computer = self.node.computer

aiida/engine/processes/process.py

@@ -41,6 +41,7 @@
 import plumpy.persistence
 from plumpy.process_states import Finished, ProcessState
 import plumpy.processes
+from plumpy.utils import AttributesFrozendict
 
 from aiida import orm
 from aiida.common import exceptions
@@ -233,6 +234,15 @@ def uuid(self) -> str:  # type: ignore[override]
         """
         return self.node.uuid
 
+    @property
+    def inputs(self) -> AttributesFrozendict:
+        """Return the inputs attribute dictionary or an empty one.
+
+        This overrides the property of the base class because that can also return ``None``. This override ensures
+        calling functions that they will always get an instance of ``AttributesFrozenDict``.
+        """
+        return super().inputs or AttributesFrozendict()
+
     @property
     def metadata(self) -> AttributeDict:
         """Return the metadata that were specified when this process instance was launched.
@@ -953,7 +963,7 @@ def exposed_inputs(
             else:
                 inputs = self.inputs
                 for part in sub_namespace.split('.'):
-                    inputs = inputs[part]  # type: ignore[index]
+                    inputs = inputs[part]
                 try:
                     port_namespace = self.spec().inputs.get_port(sub_namespace)  # type: ignore[assignment]
                 except KeyError:

aiida/engine/processes/workchains/restart.py

@@ -178,7 +178,7 @@ def should_run_process(self) -> bool:
         This is the case as long as the last process has not finished successfully and the maximum number of restarts
         has not yet been exceeded.
         """
-        max_iterations = self.inputs.max_iterations.value  # type: ignore[union-attr]
+        max_iterations = self.inputs.max_iterations.value
         return not self.ctx.is_finished and self.ctx.iteration < max_iterations
 
     def run_process(self) -> ToContext:
@@ -311,7 +311,7 @@ def results(self) -> Optional['ExitCode']:
         # We check the `is_finished` attribute of the work chain and not the successfulness of the last process
         # because the error handlers in the last iteration can have qualified a "failed" process as satisfactory
         # for the outcome of the work chain and so have marked it as `is_finished=True`.
-        max_iterations = self.inputs.max_iterations.value  # type: ignore[union-attr]
+        max_iterations = self.inputs.max_iterations.value
         if not self.ctx.is_finished and self.ctx.iteration >= max_iterations:
             self.report(
                 f'reached the maximum number of iterations {max_iterations}: '
@@ -392,7 +392,7 @@ def on_terminated(self):
         """Clean the working directories of all child calculation jobs if `clean_workdir=True` in the inputs."""
         super().on_terminated()
 
-        if self.inputs.clean_workdir.value is False:  # type: ignore[union-attr]
+        if self.inputs.clean_workdir.value is False:
             self.report('remote folders will not be cleaned')
             return
 

docs/source/nitpick-exceptions

@@ -135,6 +135,7 @@ py:class paramiko.proxy.ProxyCommand
 # These can be removed once they are properly included in the `__all__` in `plumpy`
 py:class plumpy.ports.PortNamespace
 py:class plumpy.utils.AttributesDict
+py:class plumpy.utils.AttributesFrozendict
 py:class plumpy.process_states.State
 py:class plumpy.workchains._If
 py:class plumpy.workchains._While