CLI: Fix exception for verdi plugin list (#6560)

In e952d77 a bug in `verdi plugin list`
was fixed where the conditional to check whether the plugin was a
process class would always raise an `AttributeError` if the plugin was
not a `Process` or a proces function. As a result, the code would never
get to the else-clause.

The else-clause contained itself another bug, which was now revealed by
the fixing of the bug in the conditional. The else-clause would call the
`get_description` classmethod of the plugin, but no classes in AiiDA
that are pluginnable even define such a class method. Probably, the
original author confused it with the instance method `get_description`
but the `verdi plugin list` command just deals with the class.

The `get_description` call is replaced with just getting `__doc__` which
returns the docstring of the class/function, or `None` if it is not
defined. In the latter case, a default message is displayed saying that
no description is available.

Since the else-clause code was never reached before the recent fix and
the `get_description` method was never supported officially by AiiDA's
pluginnable interfaces, it is fine to just change this behavior.

src/aiida/cmdline/commands/cmd_plugin.py

@@ -47,14 +47,13 @@ def plugin_list(entry_point_group, entry_point):
         except EntryPointError as exception:
             echo.echo_critical(str(exception))
         else:
-            try:
-                if (inspect.isclass(plugin) and issubclass(plugin, Process)) or (
-                    hasattr(plugin, 'is_process_function') and plugin.is_process_function
-                ):
-                    print_process_info(plugin)
-                else:
-                    echo.echo(str(plugin.get_description()))
-            except AttributeError:
+            if (inspect.isclass(plugin) and issubclass(plugin, Process)) or (
+                hasattr(plugin, 'is_process_function') and plugin.is_process_function
+            ):
+                print_process_info(plugin)
+            elif plugin.__doc__:
+                echo.echo(plugin.__doc__)
+            else:
                 echo.echo_error(f'No description available for {entry_point}')
     else:
         entry_points = get_entry_point_names(entry_point_group)

tests/cmdline/commands/test_plugin.py

@@ -11,7 +11,7 @@
 import pytest
 from aiida.cmdline.commands import cmd_plugin
 from aiida.parsers import Parser
-from aiida.plugins import CalculationFactory, ParserFactory, WorkflowFactory
+from aiida.plugins import BaseFactory
 from aiida.plugins.entry_point import ENTRY_POINT_GROUP_TO_MODULE_PATH_MAP
 
 
@@ -43,6 +43,7 @@ def test_plugin_list_non_existing(run_cli_command):
     'entry_point_string',
     (
         'aiida.calculations:core.arithmetic.add',
+        'aiida.data:core.array',
         'aiida.workflows:core.arithmetic.multiply_add',
         'aiida.workflows:core.arithmetic.add_multiply',
     ),
@@ -52,24 +53,20 @@ def test_plugin_list_detail(run_cli_command, entry_point_string):
     from aiida.plugins.entry_point import parse_entry_point_string
 
     entry_point_group, entry_point_name = parse_entry_point_string(entry_point_string)
-    factory = CalculationFactory if entry_point_group == 'aiida.calculations' else WorkflowFactory
-    entry_point = factory(entry_point_name)
+    entry_point = BaseFactory(entry_point_group, entry_point_name)
 
     result = run_cli_command(cmd_plugin.plugin_list, [entry_point_group, entry_point_name])
     assert entry_point.__doc__ in result.output
 
 
-class CustomParser(Parser):
-    @classmethod
-    def get_description(cls) -> str:
-        return 'str69'
+class NoDocStringPluginParser(Parser):
+    pass
 
 
-def test_plugin_description(run_cli_command, entry_points):
-    """Test that ``verdi plugin list`` uses ``get_description`` if defined."""
-
-    entry_points.add(CustomParser, 'aiida.parsers:custom.parser')
-    assert ParserFactory('custom.parser') is CustomParser
+def test_plugin_list_no_docstring(run_cli_command, entry_points):
+    """Test ``verdi plugin list`` does not fail if the plugin does not define a docstring."""
+    entry_points.add(NoDocStringPluginParser, 'aiida.parsers:custom.parser')
+    assert BaseFactory('aiida.parsers', 'custom.parser') is NoDocStringPluginParser
 
     result = run_cli_command(cmd_plugin.plugin_list, ['aiida.parsers', 'custom.parser'])
-    assert result.output.strip() == 'str69'
+    assert result.output.strip() == 'Error: No description available for custom.parser'