I thought of a better place to trigger extension installation rather than argparse._check_value. argparse._check_value is already too deep.

How about we check whether the command is in the command_table or command_group_table after they are full-loaded:

This will be very easy with the extraction of extension installation logic from _check_value (#17474).

As for the behavior of argparse, it is expected that -s is skipped during parsing and marked as unrecognized later.

We can repro with

import argparse

# create the top-level parser
parser = argparse.ArgumentParser(prog='PROG')
subparsers = parser.add_subparsers(help='sub-command help')

# create the parser for the "a" command
parser_a = subparsers.add_parser('a', help='a help')
parser_a.add_argument('--bar', type=int, help='bar help')

print(parser.parse_args('--bar a'.split()))

usage: PROG [-h] {a} ...
PROG: error: unrecognized arguments: --bar

So checking whether the command is valid is much easier than altering the behavior of argparse.

I thought of a better place to trigger extension installation rather than argparse._check_value. argparse._check_value is alrady too deep.

How about we check whether the command is in the command_table or command_group_table after they are full-loaded:

azure-cli/src/azure-cli-core/azure/cli/core/__init__.py

Lines 452 to 460 in 1ca05db

	# No module found from the index. Load all command modules and extensions
	logger.debug("Loading all modules and extensions")
	_update_command_table_from_modules(args)
	ext_suppressions = _get_extension_suppressions(self.loaders)
	# We always load extensions even if the appropriate module has been loaded
	# as an extension could override the commands already loaded.
	_update_command_table_from_extensions(ext_suppressions)
	logger.debug("Loaded %d groups, %d commands.", len(self.command_group_table), len(self.command_table))

This will be very easy with the extraction of extension installation logic from _check_value (#17474).

Thanks for the suggestion. I will check long-term solutions later.