Doing a loop with a Taskfile and go-task

Taskfile.yml

# https://taskfile.dev

# Run with no files
# task demo:emtpy
# Run with some files
# task demo:non-empty

version: '3'

vars:
  GREETING: Hello, World!
  ITEMS: '[ 1, 2, 3, 4, 8 ]'


tasks:
  _loop_end: {}
  _loop_tasks:
    desc: |
      Loop over tasks in the `_loop_tasks` variable.

      `_loop_tasks` should be a JSON string with objects that have
      `name` and `args` attributes, e.g.

      ```
      [
        { "name": "task1", "args": { "a": 1 } },
        { "name": "task2", "args": { "b": 2 } }
      ]
      ```

      The name is the name of the task to run, and the args attribute
      will be passed to the task in a variable called `_loop_task_args`.
    cmds:
      - echo 'loop_tasks={{._loop_tasks}}'
      - echo 'loop_task={{._loop_task}}'
      - task: '{{(._loop_task | mustFromJson).name}}'
        vars:
          _loop_task_args: '{{(._loop_task | mustFromJson).args | mustToJson}}'
      - task: '{{if gt (._loop_tasks| mustFromJson | len) 1}}_loop_tasks{{else}}_loop_end{{end}}'
        vars:
          _loop_tasks: "{{._loop_tasks | mustFromJson | rest | mustToJson}}"
    vars:
      _loop_task: '{{((._loop_tasks | mustFromJson | first | default (dict "name" "_loop_end" )) | mustToJson)}}'

  demo:non-empty:
    cmds:
      - task: clean
      - task: files:generate
      - task: files:cksum

  demo:empty:
    cmds:
      - task: clean
      - task: files:cksum

  default:
    cmds:
      - task: _loop_tasks
        vars:
          _loop_tasks: |
            [
              { "name": "_do_a", "args": {"a":1} },
              { "name": "_do_b", "args": {"b":2} },
              { "name": "_do_c", "args": {"c":3} }
            ]

  _do_a:
    cmds:
      - echo doing a 'args={{._loop_task_args}}}' 'arg={{(mustFromJson ._loop_task_args).a}}'

  _do_b:
    cmds:
      - echo doing b 'args={{._loop_task_args}}}' 'arg={{(mustFromJson ._loop_task_args).b}}'

  _do_c:
    cmds:
      - echo doing c 'args={{._loop_task_args}}}' 'arg={{(mustFromJson ._loop_task_args).c}}'

  # ...

  dynamic:
    - task: files:generate
    - task: files:cksum

  files:generate:
    cmds:
      # generate files ...
      - |
        mkdir -vp tmp/files
        for i in {0..2}; do
          echo "file $i" > "tmp/files/file$i.txt"
        done

  files:cksum:
    cmds:
      - cmd: |
          echo '_loop_tasks={{._loop_tasks}}'
          echo 'TXT_FILES={{.TXT_FILES}}'
      - task: _loop_tasks
        vars:
          _loop_tasks: |
            [
            {{if .TXT_FILES}}
            {{range $index, $file := (.TXT_FILES | splitList "\n" | sortAlpha)}}
              {{- if gt $index 0}},{{end -}}
              {
                "name": "_cksum_file",
                "args": {
                  "FILE_NAME": {{$file | mustToJson}},
                  "INDEX": {{$index | mustToJson}}
                }
              }
            {{end}}
            {{end}}
            ]
    vars:
      TXT_FILES:
        sh: shopt -s globstar nullglob; printf "%s\n" ./tmp/files/**/*.txt


  _cksum_file:
    cmds:
      - cksum {{.FILE_NAME}}
    vars:
      FILE_NAME: '{{ .FILE_NAME | default (._loop_task_args | mustFromJson).FILE_NAME }}'

  clean:
    cmds:
      - rm -vrf tmp