cli: show default values in config args log #18611

This PR expands the config args listing that shows up at boot. The motivation for this PR is based on this old issue from 2016: #8165

However, this PR isn't changing anything in the UI and only changes the output of the config args list in debug.log.

The proposed config arg list would like this:

2020-04-12T20:35:30Z Config file arg: [main] daemon="1"
2020-04-12T20:35:30Z Config file arg: [main] deprecatedrpc="signrawtransaction"
2020-04-12T20:35:30Z Config file arg: [main] listen="1", default=1
2020-04-12T20:35:30Z Config file arg: [main] port="8444", default=8333
2020-04-12T20:35:30Z Config file arg: [main] prune="550", default=0
2020-04-12T20:35:30Z Config file arg: [main] rest="1", default=0
2020-04-12T20:35:30Z Config file arg: [main] rpcallowip="127.0.0.1"
2020-04-12T20:35:30Z Config file arg: [main] rpcbind=****, default=127
2020-04-12T20:35:30Z Config file arg: [main] rpcpassword=****
2020-04-12T20:35:30Z Config file arg: [main] rpcport="8445", default=8332
2020-04-12T20:35:30Z Config file arg: [main] rpcuser=****
2020-04-12T20:35:30Z Config file arg: [main] server="1"
2020-04-12T20:35:30Z Config file arg: [regtest] blockfilterindex="basic", default=0
2020-04-12T20:35:30Z Config file arg: [regtest] daemon="0"
2020-04-12T20:35:30Z Config file arg: [regtest] listen="1", default=1
2020-04-12T20:35:30Z Config file arg: [regtest] rest="1", default=0
2020-04-12T20:35:30Z Config file arg: [regtest] rpcallowip="127.0.0.1"
2020-04-12T20:35:30Z Config file arg: [regtest] rpcbind=****, default=127
2020-04-12T20:35:30Z Config file arg: [regtest] server="1"
2020-04-12T20:35:30Z Config file arg: [regtest] upnp="0", default=0
2020-04-12T20:35:30Z Config file arg: [test] daemon="1"
2020-04-12T20:35:30Z Config file arg: [test] deprecatedrpc="signrawtransaction"
2020-04-12T20:35:30Z Config file arg: [test] listen="1", default=1
2020-04-12T20:35:30Z Config file arg: [test] prune="550", default=0
2020-04-12T20:35:30Z Config file arg: [test] rest="1", default=0
2020-04-12T20:35:30Z Config file arg: [test] rpcallowip="127.0.0.1"
2020-04-12T20:35:30Z Config file arg: [test] rpcbind=****, default=127
2020-04-12T20:35:30Z Config file arg: [test] server="1"

Only those args that have default values set will be extended with a default= entry.

The current implementation is using a simple regex to extract default values from available argument descriptions.

<!--e57a25ab6845829454e8d69fc972939a-->

The following sections might be updated with supplementary metadata relevant to reviewers and maintainers.

<!--174a7506f384e20aa4161008e828411d-->

Conflicts

Reviewers, this pull request conflicts with the following ones:

• #16673 (Relog configuration args on debug.log rotation by LarryRuane)

If you consider this pull request important, please also help to review the conflicting pull requests. Ideally, start with the one that should be merged first.

When we add defaults, I think we should show all options, not just ones the user has changed.

Also, this can't handle complex defaults (eg, "1 unless -connect used"), so I think it's not necessarily a step in the right direction...

Maybe instead, it should iterate all the options in order, printing the current value, and where that value came from (default including soft-set, config, or command line)?

Many thanks, @luke-jr !

I will then try to implement the points you mentioned. Will also make this PR a "draft".

When we add defaults, I think we should show all options, not just ones the user has changed.

Also, this can't handle complex defaults (eg, "1 unless -connect used"), so I think it's not necessarily a step in the right direction...

Maybe instead, it should iterate all the options in order, printing the current value, and where that value came from (default including soft-set, config, or command line)?