feat: add support for Terraform modules in tflint

[colwynlegitscript]

Fixes tflint path errors when files and modules are referenced in a relative directory in Terraform and enables tflint module mode usage. tflint has to be run from the same directory as the file under test in order for relative references to work correctly.

I'm not sure if there are other updates that need to be made to the tests so I'd appreciate some guidance there. I added some Terraform that seems like the right test structure to me, but I'm perfectly happy to change it. The image built and make test returned successfully locally.

I feel a little weird about where terraform get is right now but it does work. If you'd like I can try to determine if module mode is enabled and add it to LINTER_COMMAND for TERRAFORM_TFLINT.

Proposed Changes

1. Changes directory to the location of the Terraform file under test for tflint
2. Runs terraform get before running tflint
   1. Adds the terraform binary to support this

Example

File structure of the project

$ tree -a -I '.git' .
.
├── .github
│   └── linters
│       └── .tflint.hcl
├── .gitignore
├── modules
│   ├── mymodule
│   │   ├── main.tf
│   │   └── variables.tf
│   └── templates
│       └── template.tmpl
└── src
    └── environment
        └── service
            └── main.tf

Where src/environment/service/main.tf contains

module "good_reference" {
  source = "terraform-aws-modules/s3-bucket/aws"
  version = "2.11.1"

  bucket = "test-bucket"
}

module "good_relative_reference" {
  source = "../../../modules/mymodule"

  policy_json = templatefile("../../../modules/templates/template.tmpl", {
    value = "testvalue"
  })
}

.github/linters/.tflint.hcl contains

config {
  module = true
  force = false
}

plugin "aws" {
  enabled = true
}

Testing

Current build

$ docker run -e RUN_LOCAL=true -e VALIDATE_ALL_CODEBASE=false -e VALIDATE_TERRAFORM_TFLINT=true -v "$(pwd):/tmp/lint" github/super-linter:slim-v4
# ...lots of logs i'm not including...
2022-01-05 19:37:45 [INFO]   File:[/tmp/lint/modules/mymodule/main.tf]
2022-01-05 19:37:46 [INFO]    - File:[main.tf] was linted with [tflint] successfully
2022-01-05 19:37:46 [INFO]   ---------------------------
2022-01-05 19:37:46 [INFO]   File:[/tmp/lint/modules/mymodule/variables.tf]
2022-01-05 19:37:46 [INFO]    - File:[variables.tf] was linted with [tflint] successfully
2022-01-05 19:37:46 [INFO]   ---------------------------
2022-01-05 19:37:46 [INFO]   File:[/tmp/lint/src/environment/service/main.tf]
2022-01-05 19:37:46 [ERROR]   Found errors in [tflint] linter!
2022-01-05 19:37:46 [ERROR]   Error code: 1. Command output:
------
Failed to load configurations. 2 error(s) occurred:

Error: `good_reference` module is not found. Did you run `terraform init`?

  on /tmp/lint/src/environment/service/main.tf line 7, in module "good_reference":
   7: module "good_reference" {

Error: `good_relative_reference` module is not found. Did you run `terraform init`?

  on /tmp/lint/src/environment/service/main.tf line 14, in module "good_relative_reference":
  14: module "good_relative_reference" {
------
2022-01-05 19:37:47 [INFO]   ----------------------------------------------
2022-01-05 19:37:47 [INFO]   ----------------------------------------------
2022-01-05 19:37:47 [INFO]   The script has completed
2022-01-05 19:37:47 [INFO]   ----------------------------------------------
2022-01-05 19:37:47 [INFO]   ----------------------------------------------
2022-01-05 19:37:47 [ERROR]   ERRORS FOUND in TERRAFORM_TFLINT:[1]
2022-01-05 19:37:47 [FATAL]   Exiting with errors found!

Build with this change

I tagged the image as super-linter-test

$ docker run -e RUN_LOCAL=true -e VALIDATE_ALL_CODEBASE=false -e VALIDATE_TERRAFORM_TFLINT=true -v "$(pwd):/tmp/lint" super-linter-test
# more logs i'm not including
2022-01-05 19:36:42 [INFO]   File:[/tmp/lint/modules/mymodule/main.tf]
2022-01-05 19:36:43 [INFO]    - File:[main.tf] was linted with [tflint] successfully
2022-01-05 19:36:43 [INFO]   ---------------------------
2022-01-05 19:36:44 [INFO]   File:[/tmp/lint/modules/mymodule/variables.tf]
2022-01-05 19:36:45 [INFO]    - File:[variables.tf] was linted with [tflint] successfully
2022-01-05 19:36:45 [INFO]   ---------------------------
2022-01-05 19:36:45 [INFO]   File:[/tmp/lint/src/environment/service/main.tf]
2022-01-05 19:36:49 [INFO]    - File:[main.tf] was linted with [tflint] successfully
2022-01-05 19:36:49 [INFO]   ----------------------------------------------
2022-01-05 19:36:49 [INFO]   ----------------------------------------------
2022-01-05 19:36:49 [INFO]   The script has completed
2022-01-05 19:36:49 [INFO]   ----------------------------------------------
2022-01-05 19:36:49 [INFO]   ----------------------------------------------
2022-01-05 19:36:49 [NOTICE]   All file(s) linted successfully with no errors detected
2022-01-05 19:36:49 [INFO]   ----------------------------------------------

Inserting errors

Just to make sure I wasn't arbitrarily making the linter pass, I removed the version from the good_reference module

$ docker run -e RUN_LOCAL=true -e VALIDATE_ALL_CODEBASE=false -e VALIDATE_TERRAFORM_TFLINT=true -v "$(pwd):/tmp/lint" super-linter-test
# more logs i'm not including
2022-01-05 20:48:02 [INFO]   File:[/tmp/lint/modules/mymodule/main.tf]
2022-01-05 20:48:03 [INFO]    - File:[main.tf] was linted with [tflint] successfully
2022-01-05 20:48:03 [INFO]   ---------------------------
2022-01-05 20:48:03 [INFO]   File:[/tmp/lint/modules/mymodule/variables.tf]
2022-01-05 20:48:04 [INFO]    - File:[variables.tf] was linted with [tflint] successfully
2022-01-05 20:48:04 [INFO]   ---------------------------
2022-01-05 20:48:04 [INFO]   File:[/tmp/lint/src/environment/service/main.tf]
2022-01-05 20:48:09 [ERROR]   Found errors in [tflint] linter!
2022-01-05 20:48:09 [ERROR]   Error code: 2. Command output:
------
Downloading registry.terraform.io/terraform-aws-modules/s3-bucket/aws 2.11.1 for good_reference...
- good_reference in .terraform/modules/good_reference
- good_relative_reference in ../../../modules/mymodule
1 issue(s) found:

Warning: module "good_reference" should specify a version (terraform_module_version)

  on main.tf line 7:
   7: module "good_reference" {

Reference: https://github.com/terraform-linters/tflint/blob/v0.34.1/docs/rules/terraform_module_version.md
------
2022-01-05 20:48:09 [INFO]   ----------------------------------------------
2022-01-05 20:48:09 [INFO]   ----------------------------------------------
2022-01-05 20:48:09 [INFO]   The script has completed
2022-01-05 20:48:09 [INFO]   ----------------------------------------------
2022-01-05 20:48:09 [INFO]   ----------------------------------------------
2022-01-05 20:48:09 [ERROR]   ERRORS FOUND in TERRAFORM_TFLINT:[1]
2022-01-05 20:48:09 [FATAL]   Exiting with errors found!

I also broke the relative module reference by choosing an invalid path ../../../broken/path/mymodule

$ docker run -e RUN_LOCAL=true -e VALIDATE_ALL_CODEBASE=false -e VALIDATE_TERRAFORM_TFLINT=true -v "$(pwd):/tmp/lint" super-linter-test
2022-01-05 20:48:41 [INFO]   File:[/tmp/lint/modules/mymodule/main.tf]
2022-01-05 20:48:42 [INFO]    - File:[main.tf] was linted with [tflint] successfully
2022-01-05 20:48:42 [INFO]   ---------------------------
2022-01-05 20:48:42 [INFO]   File:[/tmp/lint/modules/mymodule/variables.tf]
2022-01-05 20:48:44 [INFO]    - File:[variables.tf] was linted with [tflint] successfully
2022-01-05 20:48:44 [INFO]   ---------------------------
2022-01-05 20:48:44 [INFO]   File:[/tmp/lint/src/environment/service/main.tf]
2022-01-05 20:48:46 [ERROR]   Found errors in [tflint] linter!
2022-01-05 20:48:46 [ERROR]   Error code: 1. Command output:
------
Downloading registry.terraform.io/terraform-aws-modules/s3-bucket/aws 2.11.1 for good_reference...
- good_reference in .terraform/modules/good_reference
- good_relative_reference in
╷
│ Error: Unreadable module directory
│
│ Unable to evaluate directory symlink: lstat ../../../broken: no such file
│ or directory
╵

╷
│ Error: Failed to read module directory
│
│ Module directory  does not exist or cannot be read.
╵

╷
│ Error: Unreadable module directory
│
│ Unable to evaluate directory symlink: lstat ../../../broken: no such file
│ or directory
╵

╷
│ Error: Failed to read module directory
│
│ Module directory  does not exist or cannot be read.
╵

Failed to load configurations. 1 error(s) occurred:

Error: Failed to read module directory

Module directory  does not exist or cannot be read.
------
2022-01-05 20:48:46 [INFO]   ----------------------------------------------
2022-01-05 20:48:46 [INFO]   ----------------------------------------------
2022-01-05 20:48:46 [INFO]   The script has completed
2022-01-05 20:48:46 [INFO]   ----------------------------------------------
2022-01-05 20:48:46 [INFO]   ----------------------------------------------
2022-01-05 20:48:46 [ERROR]   ERRORS FOUND in TERRAFORM_TFLINT:[1]
2022-01-05 20:48:46 [FATAL]   Exiting with errors found!

Readiness Checklist

Author/Contributor

• If documentation is needed for this change, has that been included in this pull request

Reviewing Maintainer

• Label as breaking if this is a large fundamental change
• Label as either automation, bug, documentation, enhancement, infrastructure, or performance