[FEATURE]: Enable the var template key in template strings for variables

[thsig]

Feature Request

Currently, the var/variables template key is not available when resolving template keys in variables. So, for example, something like this is currently not possible:

# project config
...
variables:
  baseDomain: example.com # We want to reuse this prefix
  apiHostname: "api.${var.baseDomain}"
  webhookHostname: "webhooks.${var.baseDomain}"

Supporting this would require us to resolve var references inside variables blocks in dependency order.

Background / Motivation

Supporting this would enable users to further reduce repetition in their configs.

Suggested Implementation(s)

When resolving a variables block (e.g. for the project, or for an environment or module), construct a simple dependency graph of variable references (indexed by the variable key).

Then, resolve the variables in dependency order and incrementally populate the key/value pairs available under the var key and use them to resolve template strings further up the reference graph.

There should also be circular dependency detection with informative error messages.

How important is this feature for you/your team?

🌹 It’s a nice to have, but nice things are nice 🙂

[stale]

This issue has been automatically marked as stale because it hasn't had any activity in 90 days. It will be closed in 14 days if no further activity occurs (e.g. changing labels, comments, commits, etc.). Please feel free to tag a maintainer and ask them to remove the label if you think it doesn't apply. Thank you for submitting this issue and helping make Garden a better product!

[stale]

This issue has been automatically marked as stale because it hasn't had any activity in 90 days. It will be closed in 14 days if no further activity occurs (e.g. changing labels, comments, commits, etc.). Please feel free to tag a maintainer and ask them to remove the label if you think it doesn't apply. Thank you for submitting this issue and helping make Garden a better product!

[stale]

This issue has been automatically marked as stale because it hasn't had any activity in 90 days. It will be closed in 14 days if no further activity occurs (e.g. changing labels, comments, commits, etc.). Please feel free to tag a maintainer and ask them to remove the label if you think it doesn't apply. Thank you for submitting this issue and helping make Garden a better product!

[stale]

This issue has been automatically marked as stale because it hasn't had any activity in 90 days. It will be closed in 14 days if no further activity occurs (e.g. changing labels, comments, commits, etc.). Please feel free to tag a maintainer and ask them to remove the label if you think it doesn't apply. Thank you for submitting this issue and helping make Garden a better product!

[Orzelius]

@thsig do we still want this?

[stefreak]

This is possible in the next release with #6745

[stefreak]

Will be fully resolved in #6814