* Make Swift 6 the minimum version
* Remove CI runs for older Swift versions
* Move from Result to typed throws in parser
* Refactor plugin code into shared files
* Readme/docs updates

In some use cases, there is a need to have an option argument behave
like a flag.

This change introduced 4 new intialiazers to `Option` that accept a
`defaultAsFlag` value.

With the following usage:

```swift
struct Example: ParsableCommand {
    @option(defaultAsFlag: "default", help: "Set output format.")
    var format: String?
    func run() {
        print("Format: \(format ?? "none")")
    }
}
```

The `defaultAsFlag` parameter creates a hybrid that supports both patterns:
  - **Flag behavior**: `--format` (sets format to "default")
  - **Option behavior**: `--format json` (sets format to "json")
  - **No usage**: format remains `nil`

As a user of the command line tool, the `--help` output clearly distinguishes
between the the hybrid and regular usages.

```
OPTIONS:
  --format [<format>]     Set output format. (default as flag: default)
````

Note the `(default as flag: ...)` text instead of regular `(default: ...)`,
and the optional value syntax `[<value>]` instead of required `<value>`.

Fixes: #829

…yml (#887)

…via async/await (#855)

* Support async custom completion functions for AsyncParsableCommand via async/await.
* Improve ParsableArguments#_errorLabel DocC.
* Fix preexisting typo.

Signed-off-by: Ross Goldberg <484615+rgoldberg@users.noreply.github.com>

Bumps the swiftlang-actions group with 2 updates: [swiftlang/github-workflows/.github/workflows/swift_package_test.yml](https://github.com/swiftlang/github-workflows) and [swiftlang/github-workflows/.github/workflows/soundness.yml](https://github.com/swiftlang/github-workflows).


Updates `swiftlang/github-workflows/.github/workflows/swift_package_test.yml` from 0.0.9 to 0.0.10
- [Release notes](https://github.com/swiftlang/github-workflows/releases)
- [Commits](swiftlang/github-workflows@0.0.9...0.0.10)

Updates `swiftlang/github-workflows/.github/workflows/soundness.yml` from 0.0.9 to 0.0.10
- [Release notes](https://github.com/swiftlang/github-workflows/releases)
- [Commits](swiftlang/github-workflows@0.0.9...0.0.10)

---
updated-dependencies:
- dependency-name: swiftlang/github-workflows/.github/workflows/swift_package_test.yml
  dependency-version: 0.0.10
  dependency-type: direct:production
  update-type: version-update:semver-patch
  dependency-group: swiftlang-actions
- dependency-name: swiftlang/github-workflows/.github/workflows/soundness.yml
  dependency-version: 0.0.10
  dependency-type: direct:production
  update-type: version-update:semver-patch
  dependency-group: swiftlang-actions
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Subcommand aliases already surface in --help and dump-help, but the
generate-manual tool ignored CommandInfoV0.aliases. Single-page output
now lists aliases inline with the subcommand name (e.g. "multiply, mul"),
matching the --help format. Multi-page output lists aliases as
comma-separated .Nm entries in the NAME section, following the BSD mdoc
convention (see ls(1)).

Resolves #851.

When a user declares `@Flag(...) var x: Bool?` without the required
`inversion:` parameter, overload resolution falls through to the
`Flag where Value == Int` initializer and the compiler reports
"requires the types 'Bool?' and 'Int' be equivalent", which does not
point the user at the real cause.

Add an `@available(*, unavailable)` init overload on
`Flag where Value == Bool?` with a message that names the missing
parameter. Follows the same pattern used for the unavailable no-arg
`Flag.init()` at the top of the file.

Resolves #835.

Failing for reasons unknown; tracked in #896.

This simplifies declaring alternate names by allowing just
a string representation of an option or flag name. The string
is parsed to split on spaces, and then validates that each
name has either a one or two dash prefix and is ASCII only.

Existing style:

    @Flag(name: [.customLong("hex-output"), .customShort("x")])
    var hexadecimalOutput = false

New style:

    @Flag(name: "--hex-output -x")
    var hexadecimalOutput = false