feat: add ALIAS special var

[DanStory]

Adds ALIAS to special vars that represents the alias that was used when invoking the task, otherwise will be the task name.

> go run ./cmd/task --dir testdata/special_vars echo-task-alias
task: [print-task-alias] echo "echo-task-alias"
echo-task-alias

> go run ./cmd/task --dir testdata/special_vars print-task-alias
task: [print-task-alias] echo "print-task-alias"
print-task-alias

[andreynering]

Hey @DanStory,

The implementation is pretty simple, so I believe we could just merge it.

That said, I'm curious on what is your use case for needing this variable. Do you mind explaining?

[DanStory]

I'm curious on what is your use case for needing this variable. Do you mind explaining?

@andreynering, I am cleaning up and restructuring our monorepo's taskfiles while trying to prevent from breaking developers' current workflow via aliases that warn of the deprecation and executing the new task. We also have a lot of duplication of tasks for each application in the monorepo, so I am experimenting with ways to dedupe common tasks while keeping decent discoverability (task --list).

version: '3'
tasks:
## original tasks
#  old:dull:app1:
#    cmd: "..."
#  old:dull:app2:
#    cmd: "..."
#  old:dull:app3:
#    cmd: "..."

## refactor all the old:dull:x tasks for this single one
## gives feedback that is deprecated for new task format
  old:dull:
    desc: "DEPRECATED: use new:shiny -- <app>"
    vars:
      APP: '{{ternary "" (splitList ":" .ALIAS | last) (eq .ALIAS .TASK)}}'
    aliases:
      - old:dull:app1
      - old:dull:app2
      - old:dull:app3
    cmds:
      - 'echo "DEPRECATED: use new:shiny -- {{.APP}} OR new:shiny:{{.APP}}"'
      - task: 'new:shiny'
        silent: true
        vars:
          CLI_ARGS: '{{.APP}}'

## have not decided between using ALIAS vs CLI_ARGS for new structure
  new:shiny:
    desc: "the new shiny"
    vars:
      APP: '{{ternary .CLI_ARGS (splitList ":" .ALIAS | last) (eq .ALIAS .TASK)}}'
    aliases:
      - new:shiny:app1
      - new:shiny:app2
      - new:shiny:app3
    cmds:
      - echo "start {{.APP}}"

> go run ./cmd/task old:dull:app1
task: [old:dull] echo "DEPRECATED: use new:shiny -- app1 OR new:shiny:app1"
DEPRECATED: use new:shiny -- app1 OR new:shiny:app1
start app1

> go run ./cmd/task --dir ./testdata new:shiny -- app1
task: [new:shiny] echo "start app1"
start app1

> go run ./cmd/task --dir ./testdata new:shiny:app1
task: [new:shiny] echo "start app1"
start app1

> go run ./cmd/task --list
task: Available tasks for this project:
* new:shiny:       the new shiny                           (aliases: new:shiny:app1, new:shiny:app2, new:shiny:app3)
* old:dull:        DEPRECATED: use new:shiny -- <app>      (aliases: old:dull:app1, old:dull:app2, old:dull:app3)

[andreynering]

@DanStory Thanks for your contribution!