cli booleans avoid negatives

[faassen]

b5 wrote on #179

Instead of --no-wrap I'd prefer --wrap, which defaults to true.
IMHO using negation in boolean flag labels is confusing:
--wrap=false is clearer than --no-wrap

I agree and would like to make it work this way, but Clap doesn't do this out of the box, so I've created a separate issue to figure this out.

What works is this (where the flag defaults to true):

/// Track metrics
#[clap(long, action = clap::ArgAction::Set, default_value_t=true)]
metrics: bool

Note that this does not support --metrics by itself, only with explicit =true and =false. I think that's acceptable for flags that default to true.

Documentation generated by Clap seems reasonable:

     --metrics <METRICS>  Track metrics [default: true] [possible values: true, false]

For flags that default to false we can use Clap's normal flag mechanism:

/// Verbose mode
#[clap(long, short = 'v')]
verbose: bool,

Documentation is like this:

 --verbose            Verbose mode

Note that this is a true Clap flag: it's only used to enable something, and you can't use an explicit true or false.

I wanted to highlight this difference, though I think it's acceptable. If we want to stick with true Clap flags for the "flag is turned on by default" use case, we have to take the --no- flags route instead.

Relevant Clap issues & PRs

The general explicit flag story:

clap-rs/clap#1649

Automatic support for --no flags. Isn't implemented.

clap-rs/clap#815

This misdirected me for a bit but has to do with environment variable parsing, so it not related:

clap-rs/clap#2664

[b5]

hmmm, now that I think about it, I'm not a massive fan of mixing "true clap flags" and "boolean clap flags". I'd prefer only "true clap flags", and you're saying the only way to do that is to go the --no route?

[faassen]

You either have a boolean option, ehich can default to true, and they always need a value, and have no single letter flag (as value is required)

Or clap flag which takes no value, defaults to false, and can have a single letter version.

[faassen]

I've gone for explicit --no-wrap as opposed to --wrap=false, with no single letter shortcut, because:

• b5 is not a massive fan of mixing

• true clap flags are easier to express with Clap

• --wrap=true would never be used anyway, so we really only need one flag --no-wrap

• It doesn't matter there's no shortcut because we didn't have one for --wrap=false either.

[b5]

At this point I think we've learned that using --no-wrap is more consistent with what clap wants to do under the hood, and while it might be a small UX hit, the lack of bugs caused by going against the grain of the library we're built on should be factored in as well. --no-wrap it is, and negation-worded flags should be allowed in the CLI, just avoided if possible.