Continue improvement of flag parsing / validation. #22594

I am interested in continuing the work started here: #16097 Basically, I would like to continue the expansion of util/system.cpp CheckValid for checking of additional types (e.g: ALLOW_STRING, etc) -> then start assigning and checking.

Is this already being undertaken? If not, I'd be more than happy to pick it up.

Yes, there are a number of followups that have been stuck in review, and one way to help would be contributing review or working to fix issues came up in review comments! Followup PRs are:

• #16545 - implements ALLOW_INT ALLOW_STRING ALLOW_BOOL settings validation
• #17580 - based on #16545, enforces consistent application of ALLOW_LIST flag internally
• #17493 - based on #17580, implements ALLOW_LIST validation, forbidding multiple ambiguous non-list settings in the config file, while still allowing non-list overrides on the command line.
• #17581 - based on #17493 just makes a code simplification enabled by the previous PRs
• #17783 - based on #17580 fixes strange option interpretations when various list options are negated and adds a check to prevent this type of buggy option parsing in the future

Also may be interesting:

• #17508 - issue suggesting more settings cleanups and fixes
• #15936 - somewhat related PR switching bitcoin-qt to store node & wallet settings in settings.json so bitcoin-qt and bitcoind are not using different settings from each other