Support count.index references in blocks w/ count

[radeksimko]

Notes

#583 is not a dependency, but count.index is quite frequently used as string in various names/tags and so is important in the context of this issue.

Background

Terraform supports count.index reference within resource, data and module block and anywhere where count meta-argument is supported, for example

resource "aws_instance" "server" {
  count = 4 # create four similar EC2 instances

  ami           = "ami-a1b2c3d4"
  instance_type = "t2.micro"

  tags = {
    Name = "Server ${count.index}"
  }
}

https://www.terraform.io/language/expressions/references#block-local-values
https://www.terraform.io/language/meta-arguments/count

We don't provide any kind of support for this type of reference and if we were to do any kind of thorough validation of them we'd probably flag them as invalid today.

Expected UX

Completion

Hover

Semantic Highlighting

Proposal

• hashicorp/hcl-lang
  • Introduce BodyExtensions{Count bool} into schema.BodySchema
  • Reflect Count in decoder.PathDecoder.CandidatesAtPos()
  • Reflect Count in decoder.PathDecoder.HoverAtPos()
  • Reflect Count in decoder.PathDecoder.SemanticTokensInFile()
• hashicorp/terraform-schema
  • Replace count attribute with BodyExtensions{Count: true} in resource, data and module block bodies
• hashicorp/terraform-ls
  • bump terraform-schema & hcl-lang

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