Using ctx.obj in shell completion for a subcommand

[jwodder]

Python: 3.9.9
Click: 8.0.3

I have a script with several subcommands where the main command reads from a config file to populate the context object, and the subcommands then operate on this data in the object. Here's an MVCE:

from configparser import ConfigParser
from dataclasses import dataclass
from pathlib import Path
from typing import Dict
import click
from click.shell_completion import CompletionItem
from platformdirs import user_config_path


@dataclass
class MyObject:
    entities: Dict[str, str]


class EntityType(click.ParamType):
    def convert(self, value, _param, ctx):
        if value in ctx.obj.entities:
            return value
        else:
            self.fail(f"{value!r}: unknown entity")

    def shell_complete(self, ctx, _param, incomplete):
        return [CompletionItem(c) for c in ctx.obj.entities if c.startswith(incomplete)]


@click.group()
@click.option(
    "-c",
    "--config",
    type=click.Path(dir_okay=False, path_type=Path),
    default=user_config_path("obj-complete") / "config.cfg",
    show_default=True,
)
@click.pass_context
def main(ctx, config):
    cfg = ConfigParser()
    cfg.read(config)
    try:
        entities = cfg["entities"]
    except KeyError:
        entities = {}
    ctx.obj = MyObject(entities=entities)


@main.command()
@click.argument("entities", type=EntityType(), nargs=-1)
def foo(entities):
    for e in entities:
        print("Fooing", e)


if __name__ == "__main__":
    main()

Unfortunately, the shell completion for EntityType isn't working; when it gets triggered, the script fails with:

Traceback (most recent call last):
  File "/Users/jwodder/.local/virtualenvwrapper/venvs/tmp-c51a37fb0e04aa3/bin/obj-complete", line 8, in <module>
    sys.exit(main())
  File "/Users/jwodder/.local/virtualenvwrapper/venvs/tmp-c51a37fb0e04aa3/lib/python3.9/site-packages/click/core.py", line 1128, in __call__
    return self.main(*args, **kwargs)
  File "/Users/jwodder/.local/virtualenvwrapper/venvs/tmp-c51a37fb0e04aa3/lib/python3.9/site-packages/click/core.py", line 1048, in main
    self._main_shell_completion(extra, prog_name, complete_var)  
  File "/Users/jwodder/.local/virtualenvwrapper/venvs/tmp-c51a37fb0e04aa3/lib/python3.9/site-packages/click/core.py", line 1123, in _main_shell_completion
    rv = shell_complete(self, ctx_args, prog_name, complete_var, instruction)
  File "/Users/jwodder/.local/virtualenvwrapper/venvs/tmp-c51a37fb0e04aa3/lib/python3.9/site-packages/click/shell_completion.py", line 49, in shell_complete
    echo(comp.complete())
  File "/Users/jwodder/.local/virtualenvwrapper/venvs/tmp-c51a37fb0e04aa3/lib/python3.9/site-packages/click/shell_completion.py", line 291, in complete
    completions = self.get_completions(args, incomplete)
  File "/Users/jwodder/.local/virtualenvwrapper/venvs/tmp-c51a37fb0e04aa3/lib/python3.9/site-packages/click/shell_completion.py", line 273, in get_completions
    return obj.shell_complete(ctx, incomplete)
  File "/Users/jwodder/.local/virtualenvwrapper/venvs/tmp-c51a37fb0e04aa3/lib/python3.9/site-packages/click/core.py", line 2393, in shell_complete
    return self.type.shell_complete(ctx, self, incomplete)
  File "/Users/jwodder/.local/virtualenvwrapper/venvs/tmp-c51a37fb0e04aa3/lib/python3.9/site-packages/obj_complete.py", line 23, in shell_complete
    return [CompletionItem(c) for c in ctx.obj.entities if c.startswith(incomplete)]
AttributeError: 'NoneType' object has no attribute 'entities'

Is there a way to get the ctx.obj assignment in main() to be in effect when completing arguments for subcommands?