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>
4 files changed
tree: 451d7d2ba90091e427da6b2ff90f8b483db94a2e
  1. .github/
  2. cmd/
  3. cue/
  4. cuego/
  5. doc/
  6. encoding/
  7. internal/
  8. pkg/
  9. tools/
  10. .gitattributes
  11. .gitignore
  12. .goreleaser.yml
  13. AUTHORS
  14. CONTRIBUTING.md
  15. go.mod
  16. go.sum
  17. LICENSE
  18. README.md
README.md

GoDoc Github Go Report Card GolangCI Go 1.12+ platforms

The CUE Data Constraint Language

Configure, Unify, Execute

CUE is an open source data constraint language which aims to simplify tasks involving defining and using data.

It is a superset of JSON, allowing users familiar with JSON to get started quickly.

What is it for?

You can use CUE to

  • define a detailed validation schema for your data (manually or automatically from data)
  • reduce boilerplate in your data (manually or automatically from schema)
  • extract a schema from code
  • generate type definitions and validation code
  • merge JSON in a principled way
  • define and run declarative scripts

How?

CUE merges the notion of schema and data. The same CUE definition can simultaneously be used for validating data and act as a template to reduce boilerplate. Schema definition is enriched with fine-grained value definitions and default values. At the same time, data can be simplified by removing values implied by such detailed definitions. The merging of these two concepts enables many tasks to be handled in a principled way.

Constraints provide a simple and well-defined, yet powerful, alternative to inheritance, a common source of complexity with configuration languages.

CUE Scripting

The CUE scripting layer defines declarative scripting, expressed in CUE, on top of data. This solves three problems: working around the closedness of CUE definitions (we say CUE is hermetic), providing an easy way to share common scripts and workflows for using data, and giving CUE the knowledge of how data is used to optimize validation.

There are many tools that interpret data or use a specialized language for a specific domain (Kustomize, Ksonnet). This solves dealing with data on one level, but the problem it solves may repeat itself at a higher level when integrating other systems in a workflow. CUE scripting is generic and allows users to define any workflow.

Tooling

CUE is designed for automation. Some aspects of this are:

  • convert existing YAML and JSON
  • automatically simplify configurations
  • rich APIs designed for automated tooling
  • formatter
  • arbitrary-precision arithmetic
  • generate CUE templates from source code
  • generate source code from CUE definitions (TODO)

Download and Install

Install using Homebrew

Using Homebrew, you can install using the CUE Homebrew tap:

brew install cuelang/tap/cue

Install From Source

If you already have Go installed, the short version is:

go get -u cuelang.org/go/cmd/cue

This will install the cue command line tool.

For more details see Installing CUE.

Learning CUE

The fastest way to learn the basics is to follow the tutorial on basic language constructs.

A more elaborate tutorial demonstrating of how to convert and restructure an existing set of Kubernetes configurations is available in written form.

References

Contributing

Our canonical Git repository is located at https://cue.googlesource.com.

To contribute, please read the Contribution Guide.

To report issues or make a feature request, use the issue tracker.

Changes can be contributed using Gerrit or Github pull requests.

Contact

You can get in touch with the cuelang community in the following ways:


Unless otherwise noted, the CUE source files are distributed under the Apache 2.0 license found in the LICENSE file.

This is not an officially supported Google product.