fixed Command.get_argument_type bug with UnionType (#110)

`Command.get_argument_type` currently crashes when `UnionType` is
encountered. Add special handling for this type

src/databricks/labs/blueprint/cli.py

@@ -4,6 +4,7 @@
 import inspect
 import json
 import logging
+import types
 from collections.abc import Callable
 from dataclasses import dataclass
 
@@ -40,7 +41,10 @@ def get_argument_type(self, argument_name: str) -> str | None:
         sig = inspect.signature(self.fn)
         if argument_name not in sig.parameters:
             return None
-        return sig.parameters[argument_name].annotation.__name__
+        annotation = sig.parameters[argument_name].annotation
+        if isinstance(annotation, types.UnionType):
+            return str(annotation)
+        return annotation.__name__
 
 
 class App:

tests/unit/test_cli.py

@@ -16,6 +16,7 @@
             "address": "",
             "is_customer": "true",
             "log_level": "disabled",
+            "optional_arg": "optional",
         },
     }
 )
@@ -26,27 +27,42 @@ def test_commands():
     app = App(inspect.getfile(App))
 
     @app.command(is_unauthenticated=True)
-    def foo(name: str, age: int, salary: float, is_customer: bool, address: str = "default"):
+    def foo(
+        name: str,
+        age: int,
+        salary: float,
+        is_customer: bool,
+        address: str = "default",
+        optional_arg: str | None = None,
+    ):
         """Some comment"""
-        some(name, age, salary, is_customer, address)
+        some(name, age, salary, is_customer, address, optional_arg)
 
     with mock.patch.object(sys, "argv", [..., FOO_COMMAND]):
         app()
 
-    some.assert_called_with("y", 100, 100.5, True, "default")
+    some.assert_called_with("y", 100, 100.5, True, "default", "optional")
 
 
 def test_injects_prompts():
     some = mock.Mock()
     app = App(inspect.getfile(App))
 
     @app.command(is_unauthenticated=True)
-    def foo(name: str, age: int, salary: float, is_customer: bool, prompts: Prompts, address: str = "default"):
+    def foo(
+        name: str,
+        age: int,
+        salary: float,
+        is_customer: bool,
+        prompts: Prompts,
+        address: str = "default",
+        optional_arg: str | None = None,
+    ):
         """Some comment"""
         assert isinstance(prompts, Prompts)
-        some(name, age, salary, is_customer, address)
+        some(name, age, salary, is_customer, address, optional_arg)
 
     with mock.patch.object(sys, "argv", [..., FOO_COMMAND]):
         app()
 
-    some.assert_called_with("y", 100, 100.5, True, "default")
+    some.assert_called_with("y", 100, 100.5, True, "default", "optional")