refactor: use DTO for both inferred and declared args

forgot to add the new module :)

src/argh/dto.py

@@ -0,0 +1,85 @@
+"""
+Data transfer objects for internal usage.
+"""
+from dataclasses import dataclass, field
+from typing import Any, Callable, Dict, List, Optional, Union, Type
+
+
+class NotDefined:
+    """
+    Specifies that an argument should not be passed to
+    ArgumentParser.add_argument(), even as None
+    """
+
+
+@dataclass
+class ParserAddArgumentSpec:
+    """
+    DTO, maps CLI arg(s) onto a function arg.
+    Ends up in ArgumentParser.add_argument().
+    """
+
+    func_arg_name: Optional[str]  # TODO: make it required (needs rearranging the logic)
+    cli_arg_names: List[str]
+    is_required: Union[bool, Type[NotDefined]] = NotDefined
+    default_value: Any = NotDefined
+    nargs: Optional[str] = None
+    other_add_parser_kwargs: Dict[str, Any] = field(default_factory=dict)
+
+    # https://kislyuk.github.io/argcomplete/#specifying-completers
+    completer: Optional[Callable] = None
+
+    def update(self, other: "ParserAddArgumentSpec") -> None:
+        for name in other.cli_arg_names:
+            if name not in self.cli_arg_names:
+                self.cli_arg_names.append(name)
+
+        if other.is_required != NotDefined:
+            self.is_required = other.is_required
+
+        if other.default_value != NotDefined:
+            self.default_value = other.default_value
+
+        if other.nargs:
+            self.nargs = other.nargs
+
+        if other.completer:
+            self.completer = other.completer
+
+        self.other_add_parser_kwargs.update(other.other_add_parser_kwargs)
+
+    def get_all_kwargs(self) -> Dict[str, Any]:
+        kwargs: Dict[str, Any] = {}
+
+        if self.is_required != NotDefined:
+            kwargs["required"] = self.is_required
+
+        if self.default_value != NotDefined:
+            kwargs["default"] = self.default_value
+
+        if self.nargs:
+            kwargs["nargs"] = self.nargs
+
+        return dict(kwargs, **self.other_add_parser_kwargs)
+
+    @classmethod
+    def make_from_kwargs(cls, func_arg_name, cli_arg_names, parser_add_argument_kwargs: Dict[str, Any]) -> "ParserAddArgumentSpec":
+        """
+        Constructs and returns a `ParserAddArgumentSpec` instance
+        according to keyword arguments according to the
+        `ArgumentParser.add_argument()` signature.
+        """
+        kwargs_copy = parser_add_argument_kwargs.copy()
+        instance = cls(
+            func_arg_name=func_arg_name,
+            cli_arg_names=cli_arg_names,
+        )
+        if "required" in kwargs_copy:
+            instance.is_required = kwargs_copy.pop("required")
+        if "nargs" in kwargs_copy:
+            instance.nargs = kwargs_copy.pop("nargs")
+        if "default" in kwargs_copy:
+            instance.default_value = kwargs_copy.pop("default")
+        if kwargs_copy:
+            instance.other_add_parser_kwargs = kwargs_copy
+        return instance