Description

Add custom command attributes.

• Attributes are placed before a command definition and start with a @ character.
• Attribute invocations consist of const command call. The command's name must start with "attr ", but this prefix is not used in the invocation.
  • A command named attr env is invoked as an attribute as @env
• Several built-in attribute commands are provided as part of this PR
  • attr example: Attaches an example to the commands help text

    # Double numbers
    @example "double an int"  r#'5 | double'#   --result 10
    @example "double a float" r#'0.5 | double'# --result 1.0
    def double []: [number -> number] {
        $in * 2
    }

  • attr env: Equivalent to using def --env
  • attr wrapped: Equivalent to using def --wrapped
  • few others to be added
• If an attribute has no internal/special purpose, it's stored as command metadata that can be obtained with scope commands.
  • This allows having attributes like @test which can be used by test runners.
• This PR also makes echo const. Purpose of this is to allow custom attribute definitions using alias. As there is currently no way to define const commands, this is intended to provide a stopgap solution.

  alias "attr test" = echo
  
  @test
  def my-test-command [] {}

  scope commands | where attributes.name has "test" will return all commands that have the test attribute.
• Used the @example attribute for std examples.

User-Facing Changes

Users can add examples to their own command definitions, and add other arbitrary attributes.

Tests + Formatting

• 🟢 toolkit fmt
• 🟢 toolkit clippy
• 🟢 toolkit test
• 🟢 toolkit test stdlib

After Submitting

Add documentation about the attribute syntax and built-in attributes