Proposal: `option` variable referencing `${option:optionName}`

[DanielleMaywood]

Problem Statement

As part of our devcontainer integration work at Coder, we make use of the customizations section in devcontainer.json and devcontainer-feature.json. We have discovered a usability issue with referencing feature options inside of a customizations section. We've had to create a layer of Coder specific magic around this for the moment.

Workaround

Given the following options block for a feature to be published as ghcr.io/coder/devcontainer-features/code-server ¹:

{
  "options": {
    "port": {
      "type": "string",
      "default": "8080"
    }
  }
}

We refer to this in the customizations sections as ²:

{
  "customizations": {
    "coder": {
      "apps": [{
        "slug": "code-server",
        "url": "http://example.com:${localEnv:FEATURE_CODE_SERVER_OPTION_PORT:8080}"
      }]
    }
  }
}

Where we populate environment variables in the form FEATURE_<name>_OPTION_<option> when calling devcontainer read-configuration ³. It is important to note that we do not have access to the default value in this approach so it has to be specified twice.

Proposal

A new variable resolution approach named option.

Variable	Properties	Description
${option:optionName}	Any	The value of an option given to the feature.

Example

Following the example provided before, it would look like this:

{
  "options": {
    "host": {
      "type": "string",
      "default": "0.0.0.0"
    },
    "port": {
      "type": "string",
      "default": "8080"
    }
  },
  "customizations": {
    "coder": {
      "apps": [{
        "slug": "code-server",
        "url": "http://${option:host}:${option:port}"
      }]
    }
  }
}

Footnotes

1. https://github.com/coder/devcontainer-features/blob/137955830d2510ca856c4b2a0375313a337c526a/src/code-server/devcontainer-feature.json#L113-L117 ↩

2. https://github.com/coder/devcontainer-features/blob/137955830d2510ca856c4b2a0375313a337c526a/src/code-server/devcontainer-feature.json#L174-L188 ↩

3. https://github.com/coder/coder/pull/18576 ↩

[Roemer]

This is similar to #467 and #164 and would be very very helpful, especially for providing meta-features (eg. features based on another feature but with some additions, mostly just env-variables or some files).