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Show possible values when an arguments value is missing #3320

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2 tasks done
epage opened this issue Jan 19, 2022 · 2 comments · Fixed by #3394
Closed
2 tasks done

Show possible values when an arguments value is missing #3320

epage opened this issue Jan 19, 2022 · 2 comments · Fixed by #3394
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A-help Area: documentation, including docs.rs, readme, examples, etc... C-enhancement Category: Raise on the bar on expectations E-medium Call for participation: Experience needed to fix: Medium / intermediate

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@epage
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epage commented Jan 19, 2022

Please complete the following tasks

  • I have searched the discussions
  • I have searched the existing issues

Clap Version

v3.0.6

Describe your use case

Many CLIs allow using the argument without a value to list what values are available. This allows a more targeted browsing than digging in --help

Today, clap just points people to help

$ git-stack --color
    Finished dev [unoptimized + debuginfo] target(s) in 0.04s
     Running `/home/epage/src/personal/git-stack/target/debug/git-stack --color`
error: The argument '--color <WHEN>' requires a value but none was supplied

USAGE:
    git-stack [OPTIONS]

For more information try --help

Describe the solution you'd like

For example:

$ cargo test --test    
error: "--test" takes one argument.                                      
Available tests:                    
    builder     
    derive                                                               
    derive_ui                       
    examples                                                             
    macros                                                                                                                                         
    yaml

(granted, this is dynamically generating the list)

We could also list the PossibleValue::help like in #3312.

Alternatives, if applicable

No response

Additional Context

No response
@epage epage added C-enhancement Category: Raise on the bar on expectations A-help Area: documentation, including docs.rs, readme, examples, etc... E-medium Call for participation: Experience needed to fix: Medium / intermediate labels Jan 19, 2022
@epage
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epage commented Jan 19, 2022

Maybe we should also have the unknown value error point people to this

Today:

$ git-stack --color lklk
    Finished dev [unoptimized + debuginfo] target(s) in 0.04s
     Running `/home/epage/src/personal/git-stack/target/debug/git-stack --color lklk`
error: Invalid value for '--color <WHEN>': Unknown color choice 'lklk'

For more information try --help

$ git-stack --color
    Finished dev [unoptimized + debuginfo] target(s) in 0.04s
     Running `/home/epage/src/personal/git-stack/target/debug/git-stack --color`
error: The argument '--color <WHEN>' requires a value but none was supplied

USAGE:
    git-stack [OPTIONS]

For more information try --help

Potential future:

$ git-stack --color lklk
    Finished dev [unoptimized + debuginfo] target(s) in 0.04s
     Running `/home/epage/src/personal/git-stack/target/debug/git-stack --color lklk`
error: Invalid value for '--color <WHEN>': Unknown color choice 'lklk'

For valid color choices try `git-stack --color`
For more information try `git-stack --help`

$ git-stack --color
    Finished dev [unoptimized + debuginfo] target(s) in 0.04s
     Running `/home/epage/src/personal/git-stack/target/debug/git-stack --color`
error: The argument '--color <WHEN>' requires a value but none was supplied

Possible values:
- auto
- always
- never
- 
For more information try `git-stack --help`

@epage
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epage commented Jan 19, 2022

Correction: looks like I wasn't using possible_values. The error is actually

$ cargo run -- --color foo
    Finished dev [unoptimized + debuginfo] target(s) in 0.02s
     Running `/home/epage/src/personal/concolor/target/debug/concolor-example --color foo`
error: "foo" isn't a valid value for '--color <WHEN>'
        [possible values: always, auto, never]

USAGE:
    concolor-example --color <WHEN>

For more information try --help

epage added a commit to epage/clap that referenced this issue Feb 2, 2022
@epage
feat(error): Show possible values when none are supplied
9d482d0 
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 clap-rs#3320
@epage epage mentioned this issue Feb 2, 2022
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A-help Area: documentation, including docs.rs, readme, examples, etc... C-enhancement Category: Raise on the bar on expectations E-medium Call for participation: Experience needed to fix: Medium / intermediate
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feat(error): Show possible values when none are supplied epage/clap
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