Can't parse Terraform variable field: nullable

[lostplan]

• terrascan version: v1.13.2
• Operating System: macOS 12.2.1

Description

After adding nullable = false to a variable definition, terrascan can no longer parse the file.

See https://www.terraform.io/language/values/variables#disallowing-null-input-values for documentation of the field.

Here is a minimal example:

terraform {
}

variable "in" {
  type     = string
  nullable = false
}

resource "null_resource" "test_resource" {
  triggers = {
    input_value = var.in
  }
}

What I Did

Terraform validates OK:

$ terraform validate
Success! The configuration is valid.

The terrascan scan also appears to be successful:

$ terrascan scan --iac-type terraform
Scan Summary -

	File/Folder         :	/path/to/terrascan-test
	IaC Type            :	terraform
	Scanned At          :	2022-03-02 09:19:21.960337 +0000 UTC
	Policies Validated  :	786
	Violated Policies   :	0
	Low                 :	0
	Medium              :	0
	High                :	0

However the process exited with code 4 (“scan summary has errors but no violations” – https://runterrascan.io/docs/usage/command_line_mode/):

$ echo $?
4

Enabling debug logging shows the error:

$ terrascan scan --iac-type terraform --log-level debug

2022-03-02T09:29:52.023Z	debug	commons/load-dir.go:146	failed to load terraform config dir '/path/to/terrascan-test'. error from terraform:
/path/to/terrascan-test/main.tf:6,3-11: Unsupported argument; An argument named "nullable" is not expected here.

[leadenmoth]

This is still a bug in v1.18.0. Looking at code in #1211 I can't see how it was related to this issue or #1182 - the issue is that valid terraform syntax isn't recognized, not that the message is imprecise

[davidjeddy]

Related / Duplicate of #1266 ?

[leadenmoth]

@davidjeddy this is actually the earliest mention of this bug, as far as I can find, but it is incorrectly closed by an unrelated fix. A few more duplicates are listed at the end of this comment: #1547 (comment)
I'm not sure if our team is still using terrascan and waiting for a fix at this point, or have replaced it with something else