This is inspired by cargo which allows you to run `cargo test --test`
and it will list the possible tests (obviously we can't support that atm
because that requires a lot of runtime processing). When we do have a
static list of possible values, we can at least show those.
Fixes#3320
For some errors, we use the unroll logic to get the list of required
arguments. The usage then does the same, but without a matcher. This
was causing the lists to not match.
As a side effect, this fixed an ordering issue where we were putting the
present arg after the not-present arg. I assume its because we ended up
reporting the items twice but the first time is correctly ordered and
gets precedence.
This was split out of #3020
In clap2, `ArgMatches.args` was public but hidden. We made it private
in clap3, giving us more implementation flexibility but many people
relied on it, like to short-circuit defaulting, providing their own
`ArgRequiredElseHelp`, etc.
The main problem was how to expose this
- If we think of `ArgMatches` as a container (a DAG), should we have an
`is_empty` and what all is included in that, like subcommands?
- If we focus on only args, what term how do we refer to this to convey
the right intent?
In the end, I realized that this aligns most with our existing
`is_present` check and reporting if args are present fits the best
within the existing API.
I looked into also exposing iterating over the args (`present_arg_ids`)
but we have no way to expose the Id. The Id is currently private and if
we made it public, it can't be used to access any arg because it can't
implement `Key`.
This supersedes #3265
If a value must be reused later then it's better to pass it as a &str
instead of cloning it, that means the clone happens in a central
place (inside the method).
By never passing a &String those instances of the method are not monomorphized.
Saves only 0.5K, maybe not worth it in hindsight.
