rfc: Add -printconfig arg to bitcoind #15493

This PR adds the -printconfig argument to bitcoind. Like -help and -version, after printing to the console it exits.

Examples:

bitcoind -printconfig
 datadir:   /Users/joao/Library/Application Support/Bitcoin
 blocksdir: /Users/joao/Library/Application Support/Bitcoin/blocks

# network is handled
bitcoind -printconfig -regtest
 datadir:   /Users/joao/Library/Application Support/Bitcoin
 blocksdir: /Users/joao/Library/Application Support/Bitcoin/regtest/blocks

# support overriding datadir
bitcoind -datadir=/tmp -testnet -printconfig
 datadir:   /tmp
 blocksdir: /tmp/testnet3/blocks

Suggested in #15438 (comment).

If you concept ACK feel free to suggest other configs to print.

I think we could print :

• the path to the pid file
• whether or not txindex is activated
• if we listen through tor
• what we debug (which category, ips, timestamps)

Why print the block dir since you already print datadir ?

Why print the block dir since you already print datadir ?

Because depends on the network.

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Conflicts

Reviewers, this pull request conflicts with the following ones:

• #15849 (Thread names in logs and deadlock debug tools by jamesob)
• #15457 (Check std::system for -[alert|block|wallet]notify by Sjors)
• #15329 (Fix InitError() and InitWarning() content by hebasto)
• #12557 ([WIP] 64 bit iOS device support by Sjors)

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.

Concept ACK, but to prevent endless bike shedding, it should just print everything except passwords.

You mean iterate ArgsManager?

Yes, that might be useful to see which options override others. So ideally do this after the parameter interaction stuff. In that case it won't complete if there's a problem, but those problems generally have their own error message which should contain enough information.

concept ACK, it might be completely redundant, but printing explicitly which file is being used as conf would be useful.

Yes, that might be useful to see which options override others. So ideally do this after the parameter interaction stuff. In that case it won't complete if there's a problem, but those problems generally have their own error message which should contain enough information.

I tend to agree. If you're going to do this, print everything that can be printed, I guess apart from really sensitive options (purely to prevent shoulder surfing, as any user being able to run this will have by definition access to bitcoin.conf, unlike the case for an equivalent RPC command).

Concept ACK.

In order to print everything I have to move the default from GetArg(..., default_value) to AddArg(...). Is this acceptable?

Concept ACK

@promag IMO we should probably do that anyway.

Perhaps also print it in a format that could be put directly in a bitcoin.conf if so desired?

<!--cf906140f33d8803c4a75a2196329ecb-->Needs rebase

Concept ACK

<!--5fd3d806e98f4a0ca80977bb178665a0-->There hasn't been much activity lately and the patch still needs rebase, so I am closing this for now. Please let me know when you want to continue working on this, so the pull request can be re-opened.

I'll pick this again once flags are settled.