tree 451d7d2ba90091e427da6b2ff90f8b483db94a2e
parent 2ca34b374463d70215976a267c9b6b967841a54f
author Adieu <adieu@adieu.me> 1575626386 +0100
committer Marcel van Lohuizen <mpvl@golang.org> 1575626511 +0000

cmd/cue/cmd: control task dependency using before and after fields

Currently we resolve task dependency by checking reference to incomplete task variable. We cannot do things like `create a file first, then run a command with it`.

For example this command would not work cause `write` and `ansible` will be executed at the same time.

```
command: play: {
	task: write: file.Create & {
		filename: "playbook.yml"
		contents:  yaml.MarshalStream([playbook])
	}
	task: ansible: exec.Run & {
		cmd:    "ansible-playbook playbook.yml"
		stdout: string
	}
	task: display: cli.Print & {
		text: task.ansible.stdout
	}
}
```

Using this PR, we could declare dependency and reverse dependency using `before` and `after` fields. The value could be either a task or a list of tasks. Now we can rewrite the command like this to make it work.

```
command: play: {
	task: write: file.Create & {
		filename: "playbook.yml"
		contents:  yaml.MarshalStream([playbook])
	}
	task: ansible: exec.Run & {
		cmd:    "ansible-playbook playbook.yml"
		stdout: string
		after: task.write
	}
	task: display: cli.Print & {
		text: task.ansible.stdout
	}
}
```

Closes #200
https://github.com/cuelang/cue/pull/200

GitOrigin-RevId: 362c703d71dd425654f52d3e7aecf811cffa4a19
Change-Id: I075b871745f2b5dc18788d2d0c02d0623fced6c4
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/4340
Reviewed-by: Marcel van Lohuizen <mpvl@golang.org>