Fix dynamic defaults (pantsbuild#14637)

After doing the work to switch the remaining subsystem options to the new style I hit some mypy errors. This fixes those (and adds tests to ensure we don't hit them again).

[ci skip-rust]
[ci skip-build-wheels]

src/python/pants/option/option_types.py

@@ -29,15 +29,17 @@ class OptionsInfo:
 # subsytem type and returning a value. E.g. `prop = Option(..., default=lambda cls: cls.default)`.
 # This is necessary to support "base" subsystem types which are subclassed with more specific
 # values.
-_DynamicDefaultT = Callable[[_SubsystemType], _DefaultT]
+# NB: Marking this as `Callable[[_SubsystemType], _DefaultT]` will upset mypy at the call site
+# because mypy won't be able to have enough info to deduce the correct type.
+_DynamicDefaultT = Callable[[_SubsystemType], Any]
 # The type of the `default` parameter for each option.
-_MaybeDynamicT = Union[_DynamicDefaultT[_DefaultT], _DefaultT]
+_MaybeDynamicT = Union[_DynamicDefaultT, _DefaultT]
 # The type of the `help` parameter for each option.
 _HelpT = _MaybeDynamicT[str]
 
 
 def _eval_maybe_dynamic(val: _MaybeDynamicT[_DefaultT], subsystem_cls: _SubsystemType) -> _DefaultT:
-    return val(subsystem_cls) if inspect.isfunction(val) else val  # type: ignore[operator,return-value]
+    return val(subsystem_cls) if inspect.isfunction(val) else val  # type: ignore[operator,return-value,no-any-return]
 
 
 class _OptionBase(Generic[_OptT, _DefaultT]):
@@ -51,7 +53,7 @@ class _OptionBase(Generic[_OptT, _DefaultT]):
     """
 
     _flag_names: tuple[str, ...]
-    _default: _DefaultT
+    _default: _MaybeDynamicT[_DefaultT]
     _help: _HelpT
     _extra_kwargs: dict[str, Any]
 
@@ -60,7 +62,7 @@ class _OptionBase(Generic[_OptT, _DefaultT]):
     def __new__(
         cls,
         *flag_names: str,
-        default: _DefaultT,
+        default: _MaybeDynamicT[_DefaultT],
         help: _HelpT,
         # Additional bells/whistles
         advanced: bool | None = None,
@@ -150,7 +152,7 @@ class _ListOptionBase(
     def __new__(
         cls,
         *flag_names: str,
-        default: list[_ListMemberT] = [],
+        default: _MaybeDynamicT[list[_ListMemberT]] = [],
         help: _HelpT,
         # Additional bells/whistles
         advanced: bool | None = None,
@@ -382,9 +384,7 @@ def __new__(
         cls,
         *flag_names: str,
         enum_type: type[_EnumT],
-        # NB: Marking this as `_DynamicDefaultT[_EnumT]` will upset mypy at the call site because
-        # mypy won't be able to have enough info to deduce the correct type.
-        default: _DynamicDefaultT[Any],
+        default: _DynamicDefaultT,
         help: _HelpT,
         # Additional bells/whistles
         advanced: bool | None = None,
@@ -509,9 +509,7 @@ def __new__(
         cls,
         *flag_names: str,
         enum_type: type[_EnumT],
-        # NB: Marking this as `_DynamicDefaultT[list[_EnumT]]` will upset mypy at the call site
-        # because mypy won't be able to have enough info to deduce the correct type.
-        default: _DynamicDefaultT[Any],
+        default: _DynamicDefaultT,
         help: _HelpT,
         # Additional bells/whistles
         advanced: bool | None = ...,
@@ -627,7 +625,7 @@ class DictOption(_OptionBase["dict[str, _ValueT]", "dict[str, _ValueT]"], Generi
     def __new__(
         cls,
         *flag_names,
-        default: dict[str, _ValueT] = {},
+        default: _MaybeDynamicT[dict[str, _ValueT]] = {},
         help,
         advanced: bool | None = None,
         daemon: bool | None = None,

src/python/pants/option/option_types_test.py

@@ -134,7 +134,7 @@ def __init__(self):
         dyn_enum_list_prop = EnumListOption(
             "--dyn-enum-list-opt",
             enum_type=MyEnum,
-            default=lambda cls: [cls.dyn_default],
+            default=lambda cls: cls.dyn_default_list,
             help=lambda cls: f"{cls.dyn_help}",
         )
         defaultless_enum_list_prop = EnumListOption(
@@ -146,6 +146,7 @@ def __init__(self):
     class MySubsystem(MyBaseSubsystem):
         dyn_help = "Dynamic Help"
         dyn_default = MyEnum.Val1
+        dyn_default_list = [MyEnum.Val1]
 
     register = Mock()
     MySubsystem.register_options(register)
@@ -265,6 +266,8 @@ def __init__(self):
         file_list_opt = FileListOption("--opt", help="")
         shellstr_list_opt = ShellStrListOption("--opt", help="")
         memorysize_list_opt = MemorySizeListOption("--opt", help="")
+        # And just test one dynamic default
+        dyn_str_list_opt = StrListOption("--opt", default=lambda cls: cls.default, help="")
 
         # Enum opts
         enum_opt = EnumOption("--opt", default=MyEnum.Val1, help="")
@@ -277,7 +280,7 @@ def __init__(self):
         enum_list_opt1 = EnumListOption("--opt", default=[MyEnum.Val1], help="")
         enum_list_opt2 = EnumListOption("--opt", enum_type=MyEnum, help="")
         dyn_enum_list_opt = EnumListOption(
-            "--opt", enum_type=MyEnum, default=lambda cls: [cls.default], help=""
+            "--opt", enum_type=MyEnum, default=lambda cls: cls.default_list, help=""
         )
         # mypy correctly complains about needing a type annotation
         enum_list_bad_opt = EnumListOption("--opt", default=[], help="")  # type: ignore[var-annotated]
@@ -291,6 +294,7 @@ def __init__(self):
         dict_opt5 = DictOption("--opt", default=dict(key="val"), help="")
         dict_opt6 = DictOption("--opt", default=dict(key=1), help="")
         dict_opt7 = DictOption("--opt", default=dict(key1=1, key2="str"), help="")
+        dyn_dict_opt = DictOption[str]("--opt", lambda cls: cls.default, help="")
 
     my_subsystem = MySubsystem()
     if TYPE_CHECKING:
@@ -322,6 +326,7 @@ def __init__(self):
         assert_type["tuple[str, ...]"](my_subsystem.file_list_opt)
         assert_type["tuple[str, ...]"](my_subsystem.shellstr_list_opt)
         assert_type["tuple[int, ...]"](my_subsystem.memorysize_list_opt)
+        assert_type["tuple[str, ...]"](my_subsystem.dyn_str_list_opt)
 
         assert_type["MyEnum"](my_subsystem.enum_opt)
         assert_type["MyEnum | None"](my_subsystem.optional_enum_opt)
@@ -339,3 +344,4 @@ def __init__(self):
         assert_type["dict[str, str]"](my_subsystem.dict_opt5)
         assert_type["dict[str, int]"](my_subsystem.dict_opt6)
         assert_type["dict[str, object]"](my_subsystem.dict_opt7)
+        assert_type["dict[str, str]"](my_subsystem.dyn_dict_opt)