Allow a default to be specified for boolean flags

[rhwood]

This allows the use of boolean flag semantics where the default behavior for the application is as if --flag had been passed, and --no-flag is not the default behavior.

[salesforce-cla]

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[codecov]

Codecov Report

Merging #41 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master      #41   +/-   ##
=======================================
  Coverage   90.39%   90.39%           
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  Files          11       11           
  Lines         302      302           
  Branches       80       80           
=======================================
  Hits          273      273           
  Misses         10       10           
  Partials       19       19

Impacted Files	Coverage Δ
src/flags.ts	100% <ø> (ø)	⬆️
src/parse.ts	91.24% <100%> (ø)	⬆️

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[jdx]

I touched on this in #34 but I'm not convinced this is very useful though. can you provide a real-world example of where you would want a default for a boolean flag?

[rhwood]

I want to be able to make the (primary or only) flag be --no-flag on the CLI, but use flags.flag within the run method and have flags.flag be true if not specified by the user. Currently flags.flag is only true if --flag is specified, and false if not specified or if --no-flag is specified.

In my specific case, I have a tool that manages a server normally run as a daemon (i.e. detached from the console and parent process), but if a user wants to run the server as not a daemon, I want the user to use the --no-daemon flag, but I also want to be able use a function to not daemonize the server if DEBUG=* or TOOL_DEBUG=1 is set, unless the user explicitly passes --daemon.

What I would really like to be able to do is have this code when writing the flags:

daemon: flags.boolean({char: 'd', allowNo: true, default: () => {return !this.config.debug}})

so that when later checking if the server should be a daemon, I can simply use (flags.daemon) instead of using (flags.daemon || !(this.config.debug && flags.daemon !== undefined)) to determine if the process should be a daemon. I think that giving the boolean flag a contextual default is significantly simpler than checking that a combination of values is acceptable later.

[jdx]

ah I see, I think this makes sense. I appreciate the explanation.

At some point I'd like to hook this together with some sort of configuration utility to make this even more hands-off so you could do what you're doing with less code.

[oclif-bot]

🎉 This PR is included in version 3.7.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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