textDocument/complete: Complete references to named values

[radeksimko]

Context

Currently the LS completes block's known attributes and nested blocks per schema and naively assumes values are static.

Terraform language supports references to named values which are generally formatted as dot-based addresses, e.g.

variable "example" {
  default = "example-value"
}
data "aws_availability_zones" "names" {
}

can be referenced as var.example or data.aws_availability_zones.names respectively elsewhere in the configuration.

Requirements

Completing the references requires LS understanding a couple of things it doesn't understand today:

• relationship between address format and block type
  • e.g. knowing that var.<name> belongs to variable block and evaluates to variable's value (which may come from its default)
• context in which references are evaluated, for example
  • local values can be referenced between each other, but variables can not
  • backend blocks do not support any kind of interpolation
  • provider blocks have limited interpolation capabilities (e.g. via alias)
  • values have types and it would be suboptimal to suggest references that do not match the destination type (e.g. var.number for a string attribute)
• whether the value is available locally within the configuration or from the state, e.g.
  • variable values would generally be local
  • data source and resource attributes would generally come from state, unless these attributes are referencing static values (such as variables)

How could we tackle this

This will likely require extensive design work to ensure stability and maintainability over time. There is a number of factors to consider, e.g.

• How does parser: Support 1st class blocks without exposed schema #36 overlap with this problem
• How will the functionality overlap with https://github.com/hashicorp/terraform/tree/master/addrs
  • we probably won't build a separate single library which decouples this logic yet, but should keep this option in mind as the risk of drifting from Terraform is real
• We may need to keep (re-)parsing the whole workspace as opposed to just open files and hold the AST for the whole workspace in memory, as references are workspace-wide, not file-wide
  • we should resolve Support workspace/didChangeWatchedFiles #15 first

For reasons above I would encourage discussing the design of the possible solution(s) here before attempting to raise a PR.

[Liquidmantis]

Since this is the issue being referenced in the issues on autocomplete, I just wanted to say that All Autocomplete has been a good workaround for me in the interim. You have to load your project files so that it's aware of variables but it's transparent otherwise.

https://marketplace.visualstudio.com/items?itemName=Atishay-Jain.All-Autocomplete

[radeksimko]

Initial support for references was added in (now merged) #485 which will be released in coming days. The same PR also includes some description of features added and links to follow-up issues covering features which were omitted from that initial PR.

With that in mind I'm going to close this issue but keep an eye out for the upcoming update (0.17.0).

[github-actions]

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