cli: render command groups, inherited flags, examples and learn-more in --help

[davlgd]

This PR teaches vlib/cli's --help rendering about four extra sections. Three are unlocked by new optional fields on Command (none of which render anything unless populated):

• group string on a sub-command — its parent's listing splits into one section per group, named after the group string verbatim followed by :. Sub-commands without a group keep falling back to the default Commands: block. Helpful for CLI with lots of commands.
• examples []string — rendered under a new Examples: section, one entry per indented line.
• learn_more string — rendered under a new Learn more: section, with newlines splitting the block into separate lines.

The fourth uses the existing Flag.global field to split inherited flags into their own section: any ancestor declared with Flag.global = true now move out of the local Flags: block into a separate Inherited flags: section, so a sub-command's own surface stays readable.

The motivation is to bring vlib/cli closer to widely-used CLI conventions (named sections, grouped sub-commands, examples, inherited flags), as recommended by the Command Line Interface Guidelines for example, while keeping V's existing Usage: / Flags: / Commands: visual style so adopting the new fields never feels like a different tool.

Rendering

Running examples/cli_groups.v with --help produces:

Usage: tasky [flags] [commands]

A tiny issue tracker CLI

Flags:
  -c  --config        Path to a tasky config file
  -h  --help          Prints help information.
  -v  --version       Prints version information.
      --man           Prints the auto-generated manpage.

Core commands:
  issue               Work with issues

Additional commands:
  config              Read or write tasky settings

Commands:
  help                Prints help information.
  version             Prints version information.
  man                 Prints the auto-generated manpage.

Examples:
  $ tasky issue list
  $ tasky issue create --title "Fix CI"
  $ tasky config get editor

Learn more:
  Use `tasky <command> --help` for details about a command.
  Documentation lives at https://example.test/tasky

Drilling into a sub-command surfaces the new Inherited flags: block:

$ tasky issue create --help
Usage: tasky issue create [flags]

Create a new issue

Flags:
  -t  --title         Title of the issue to create (required)
  -h  --help          Prints help information.
      --man           Prints the auto-generated manpage.

Inherited flags:
  -c  --config        Path to a tasky config file

A Command with none of the new fields populated and no inherited globals renders exactly like before: Usage: line, optional description, Flags:, Commands:. No new sections appear unless they have content.

How to try it

v -o tasky examples/cli_groups.v
./tasky --help
./tasky issue --help
./tasky issue create --help

The example exercises every new code path: groups (Core commands / Additional commands), an inherited global flag (-c, --config), an examples block and a multi-line learn_more block.

Tests

I've added four cases to vlib/cli/help_test.v:

• test_help_message_groups_commands_by_group_field
• test_help_message_renders_group_title_verbatim (UTF-8 safety: a group string starting with a multi-byte character renders without mojibake)
• test_help_message_separates_inherited_flags_from_locals
• test_help_message_renders_examples_and_learn_more
• test_help_message_omits_empty_optional_sections

The two pre-existing assertions in test_help_message still pass unchanged, which is the strongest evidence that apps without the new fields see identical output.

Run with:

v -enable-globals test vlib/cli/

[medvednikov]

Btw to enforce our "one way" policy I'll be keeping only flag in vlib.

cli will be moved to v install cli

[davlgd]

Got it — happy to help with that move. Two questions:

1. Should this PR (and cli: drop trailing periods and use 'Print' in default help/version/man descriptions #27123) land before the extraction, or do you prefer it goes into the new cli repo once it exists?
2. Is there work I can pick up to help with the extraction itself?

[medvednikov]

I'll merge it before the extraction. I'll do the extraction myself.