fix: display full type info for Optional/Union annotations (fixes #508)

fire/helptext.py

@@ -33,6 +33,7 @@
 
 import collections
 import itertools
+import typing
 
 from fire import completion
 from fire import custom_descriptions
@@ -524,14 +525,37 @@ def _GetArgType(arg, spec):
   """
   if arg in spec.annotations:
     arg_type = spec.annotations[arg]
+    return _FormatType(arg_type)
+  return ''
+
+
+def _FormatType(tp):
+  """Format a type annotation for display in help text.
+
+  Handles Optional, Union, and other typing constructs properly,
+  displaying e.g. Optional[str] instead of just 'Optional'.
+  """
+  origin = typing.get_origin(tp)
+  args = typing.get_args(tp)
+
+  if origin is None:
+    # Simple type like str, int, etc.
     try:
-      return arg_type.__qualname__
+      return tp.__qualname__
     except AttributeError:
-      # Some typing objects, such as typing.Union do not have either a __name__
-      # or __qualname__ attribute.
-      # repr(typing.Union[int, str]) will return ': typing.Union[int, str]'
-      return repr(arg_type)
-  return ''
+      return repr(tp)
+
+  if origin is typing.Union:
+    # Display Optional[str] as 'str | None'
+    non_none = [a for a in args if a is not type(None)]
+    if len(non_none) == 1 and len(args) == 2:
+      return f'{_FormatType(non_none[0])} | None'
+    return ' | '.join(_FormatType(a) for a in args)
+
+  # For generic types like List[str], Dict[str, int]
+  args_str = ', '.join(_FormatType(a) for a in args)
+  origin_name = getattr(origin, '__qualname__', str(origin))
+  return f'{origin_name}[{args_str}]'
 
 
 def _GetArgDefault(flag, spec):