Allow --arg Value for booleans in HfArgumentParser (#9823)

* Allow --arg Value for booleans in HfArgumentParser

* Update last test

* Better error message

src/transformers/hf_argparser.py

@@ -15,7 +15,7 @@
 import dataclasses
 import json
 import sys
-from argparse import ArgumentParser
+from argparse import ArgumentParser, ArgumentTypeError
 from enum import Enum
 from pathlib import Path
 from typing import Any, Iterable, List, NewType, Optional, Tuple, Union
@@ -25,6 +25,20 @@ DataClass = NewType("DataClass", Any)
 DataClassType = NewType("DataClassType", Any)
 
 
+# From https://stackoverflow.com/questions/15008758/parsing-boolean-values-with-argparse
+def string_to_bool(v):
+    if isinstance(v, bool):
+        return v
+    if v.lower() in ("yes", "true", "t", "y", "1"):
+        return True
+    elif v.lower() in ("no", "false", "f", "n", "0"):
+        return False
+    else:
+        raise ArgumentTypeError(
+            f"Truthy value expected: got {v} but expected one of yes/no, true/false, t/f, y/n, 1/0 (case insensitive)."
+        )
+
+
 class HfArgumentParser(ArgumentParser):
     """
     This subclass of `argparse.ArgumentParser` uses type hints on dataclasses to generate arguments.
@@ -85,11 +99,20 @@ class HfArgumentParser(ArgumentParser):
                 if field.default is not dataclasses.MISSING:
                     kwargs["default"] = field.default
             elif field.type is bool or field.type is Optional[bool]:
-                if field.type is bool or (field.default is not None and field.default is not dataclasses.MISSING):
-                    kwargs["action"] = "store_false" if field.default is True else "store_true"
                 if field.default is True:
-                    field_name = f"--no_{field.name}"
-                    kwargs["dest"] = field.name
+                    self.add_argument(f"--no_{field.name}", action="store_false", dest=field.name, **kwargs)
+
+                # Hack because type=bool in argparse does not behave as we want.
+                kwargs["type"] = string_to_bool
+                if field.type is bool or (field.default is not None and field.default is not dataclasses.MISSING):
+                    # Default value is True if we have no default when of type bool.
+                    default = True if field.default is dataclasses.MISSING else field.default
+                    # This is the value that will get picked if we don't include --field_name in any way
+                    kwargs["default"] = default
+                    # This tells argparse we accept 0 or 1 value after --field_name
+                    kwargs["nargs"] = "?"
+                    # This is the value that will get picked if we do --field_name (without value)
+                    kwargs["const"] = True
             elif hasattr(field.type, "__origin__") and issubclass(field.type.__origin__, List):
                 kwargs["nargs"] = "+"
                 kwargs["type"] = field.type.__args__[0]