Link completion specs to different versions of CLI tools

As CLI tools often change, it's important that users get the right competion spec for the specific version of a CLI tool they are one.

To allow this, Fig adds two things to your typescript completion spec file:

1. To get the version, Fig defines a special export called getVersionCommand that allows you to execute a shell command and then return the current version of a user's CLI tool.
2. To return the right completion spec, Fig allows the Fig.Spec type to be a function that takes in a verion, and outputs a normal Fig.Spec object.

Example For instance, yarn has major version 1 and major version 2. There are several commands that exist in v1 but not v2 and vice versa.

The completion spec for yarn looks a little like this:

# The completion spec is a function that returns a Fig.spec object
const completionSpec: Fig.Spec = (version: string): Fig.Spec => {

  var global_subcommands: Fig.Subcommands[] = [
    {name: "subcommand_one"},
    {name: "subcommand_two"},
  ]

  var version_one_subcommands: Fig.Subcommands[] = [
    {name: "version_one"},
  ]

  var version_one_subcommands: Fig.Subcommands[] = [
    {name: "version_two"},
  ]



    if (version === "1.0.0") return {
    name: "yarn",
    subcommands: [...global_subcommands, ...version_one_subcommands]
    }

    else return {
    name: "yarn",
    subcommands: [...global_subcommands, ...version_two_subcommands]
    }
}

export default completionSpec;


// Function that returns the semantic version for a given CLI tool. Then used to load up the relevant completion spec
export const getVersionCommand = async (executeShellCommand: fn): Promise<string> => {

  const version: string = await executeShellCommand("yarn --version")

    return version
}