c3x v0.3.8: OpenTofu support

[andreacappelletti97]

c3x now reads OpenTofu projects natively, as of v0.3.8.

c3x estimates the monthly cost of infrastructure code before you apply it, statically: no init, no credentials, no state. Until now OpenTofu projects mostly worked because the syntax is shared, but anything OpenTofu-specific was ignored or mispriced.

What works now

.tofu files. They're read alongside .tf, and a main.tofu replaces the main.tf of the same name, as OpenTofu does. Projects that ship both files so they run under either tool aren't counted twice.

Provider for_each. Each resource instance is priced in the region of the provider instance it uses:

provider "aws" {
  alias    = "by_region"
  for_each = var.regions
  region   = each.value
}

resource "aws_instance" "web" {
  for_each      = var.regions
  provider      = aws.by_region[each.key]
  instance_type = "m5.large"
}

$ c3x estimate
  aws_instance.web["euw1"]   730 hours × $0.107 = $78.11/mo
  aws_instance.web["use1"]   730 hours × $0.096 = $70.08/mo

Plan JSON from tofu show -json, the same as Terraform's.

We checked this against OpenTofu 1.12.6 itself: for a test project, c3x reads the same resources OpenTofu plans, and gives the same total from the directory as from the plan.

Also fixed, for Terraform users too

• Resources on an aliased provider were priced in the first provider's region, so multi-region configs came out at one region's rates.
• In PR comments, count/for_each instances could be compared against the wrong baseline, hiding a change to one instance.
• Several Terraform functions were missing and produced silently wrong estimates; they're implemented now, and the few still unsupported (file, templatefile) print a warning instead.

If you use c3x top --format targets with a plan JSON, please read the note at the top of the release notes — v0.3.5 to v0.3.7 emitted whole-resource targets for for_each instances.

brew upgrade c3xdev/tap/c3x

If c3x misreads something in your OpenTofu project, open an issue with the snippet. That's the fastest way to get it fixed.