CLI Serialization Fixes

[kschwab]

• Adds serialization of sub commands.
• Fixes serialization of kebab case of flags.

[hramezani]

Thanks @kschwab

Is it a fix for an issue?

[kschwab]

@hramezani yes, it is an issue I found locally. I can open a formal ticket if you would like.

CliApp.serialize is incorrect when cli_kebab_case is enabled. Currently on main it will do the below:

from pydantic_settings import BaseSettings, CliApp

class Cfg(BaseSettings, cli_kebab_case=True):
    foo_kebab: int = 123

args = CliApp.serialize(Cfg())

print(args)
#> ['--foo_kebab', '123']

CliApp.run(Cfg, cli_args=args)
"""
usage: example.py [-h] [--foo-kebab int]
example.py: error: unrecognized arguments: --foo_kebab 123
"""

With this fix, it will correctly apply the kebab case to serialization:

from pydantic_settings import BaseSettings, CliApp

class Cfg(BaseSettings, cli_kebab_case=True):
    foo_kebab: int = 123

print(CliApp.serialize(Cfg()))
#> ['--foo-kebab', '123'] 

print(CliApp.run(Cfg, cli_args=args))
#> foo_kebab=123

I also missed serialization of subcommands, which addressed as well in this PR. See added test.

[kschwab]

I also just noticed that cli_implicit_flags case will also likely need an adjustment.

[kschwab]

Ok @hramezani, this is ready for review again. When I looked closer, there were a handful of bugs I found with the original serialization. The change set looks larger then it is. I reverted the original serialization implementation, and consolidated it into two standalone functions.

The bugs I found and fixed were:

• Serialization ordering could be wrong. i.e., ordering of positionals and subcommands has to be strictly maintained.
• Skip serialization of defaults. Only modified values should be serialized.
• Handle serialization of kebab case.
• Handle implicit bool flags.

All the newly added tests currently fail on main.

[hramezani]

Thanks @kschwab, Great job!