Support for references to variables and locals

[radeksimko]

Background

As part of initial work on supporting traversal expressions (references such as aws_instance.example.public_ip) it was decided to leave out variables, locals and outputs as the data types are not statically defined in the schema for these.

Use-cases

Completion

Given a config

variable "test" {
  type = number
}

locals {
  foo = 42
}

resource "aws_lb" "example" {
  listener {
    port = # <- HERE
  }
}

user should be able to auto-complete var.test or local.foo for port field (assuming port is of number type).

Hover

Given a config

resource "aws_lb" "example" {
  listener {
    port = var.test
    protocol = local.protocol
  }
}

a popup should appear once user hovers over var.test or local.protocol with data type (e.g. string or number).

Semantic Tokens

Given a config

resource "aws_lb" "example" {
  listener {
    port = var.test
    protocol = local.protocol
  }
}

both var.test and local.protocol should be highlighted correctly via semantic tokens.

Proposal

• Expand hcl-lang's schema.BlockAddrSchema by adding BodyAsType which can help express that a variable block (referred to via var.example) is addressable as a type declared in type attribute of that block.
• Reflect BodyAsType in decoder.DecodeReferences
• Use BodyAsType in terraform-schema in the schema of the variable block within terraform-schema, e.g.
  • https://github.com/hashicorp/terraform-schema/blob/6d07fd682f6596ef668e918fa29b605e72fbffb8/internal/schema/0.12/variable_block.go#L13-L21
  • https://github.com/hashicorp/terraform-schema/blob/6d07fd682f6596ef668e918fa29b605e72fbffb8/internal/schema/0.14/variable_block.go#L12-L20
• Bump hcl-lang in terraform-schema
• Bump terraform-schema & hcl-lang in terraform-schema

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