tflint does not handle locals as expected

[TrongBYM]

Summary

Hello, I am playing around with tflint and encountered an unexpected behaviour when it comes to local values.

I have a minimal example here: https://github.com/TrongBYM/tflint-issue-example

In short, I am running tflint against a Terraform configuration that provisions 3 ECR repositories, all with invalid ECR names. I therefore expects tflint to report 3 issues with my Terraform configuration, but instead it reports only 2 issues.

According to the documentation here about local values, this behaviour seems unexpected?

Is there a limitation I am not aware of here? I did find this list of caveats, with the first point looking rather related to this case.

Command

tflint

Terraform Configuration

# My project structure (see referenced example repository!)
# .
# ├── README.md
# ├── main.tf
# └── modules
#     └── custom_ecr
#         └── main.tf

### ./main.tf

terraform {
  required_providers {
    aws = {
      source  = "hashicorp/aws"
      version = ">= 5.0, < 6.0"
    }
  }
  required_version = "~> 1.8, < 2.0"
}

module "my_ecr_repository" {
  source   = "./modules/custom_ecr"
  ecr_name = "%%%"  # Invalid ECR repository name
}


### ./modules/custom_ecr/main.tf
variable "ecr_name" {
  type    = string
}

# NOTE: The character "%" is not allowed in ECR repository names.

# tflint will catch this error
resource "aws_ecr_repository" "this" {
  name = var.ecr_name 
}

# tflint will catch this error
resource "aws_ecr_repository" "this_too" {
  name = "${var.ecr_name}-hello-world" 
}

# tflint will NOT catch this error
locals {
  ecr_name_abstraction = "${var.ecr_name}-hello-world"
}
resource "aws_ecr_repository" "this_three" {
  name = local.ecr_name_abstraction
}

TFLint Configuration

config {
  plugin_dir = ".tflint.d/plugins"
  call_module_type = "all" # have tried "local" as well, same results!
  disabled_by_default = false
}

plugin "terraform" {
  enabled = true
  preset  = "recommended"
}

plugin "aws" {
  enabled = true
  deep_check = false 
  version = "0.35.0"
  source  = "github.com/terraform-linters/tflint-ruleset-aws"
}

Output

09:34:58 config.go:177: [INFO] Load config: .tflint.hcl
09:34:58 config.go:334: [DEBUG] Config loaded
09:34:58 config.go:335: [DEBUG]   CallModuleType: all
09:34:58 config.go:336: [DEBUG]   CallModuleTypeSet: true
09:34:58 config.go:337: [DEBUG]   Force: false
09:34:58 config.go:338: [DEBUG]   ForceSet: false
09:34:58 config.go:339: [DEBUG]   DisabledByDefault: false
09:34:58 config.go:340: [DEBUG]   DisabledByDefaultSet: true
09:34:58 config.go:341: [DEBUG]   PluginDir: .tflint.d/plugins
09:34:58 config.go:342: [DEBUG]   PluginDirSet: true
09:34:58 config.go:343: [DEBUG]   Format: 
09:34:58 config.go:344: [DEBUG]   FormatSet: false
09:34:58 config.go:345: [DEBUG]   Varfiles: 
09:34:58 config.go:346: [DEBUG]   Variables: 
09:34:58 config.go:347: [DEBUG]   Only: 
09:34:58 config.go:348: [DEBUG]   IgnoreModules:
09:34:58 config.go:352: [DEBUG]   Rules:
09:34:58 config.go:356: [DEBUG]   Plugins:
09:34:58 config.go:358: [DEBUG]     aws: enabled=true, version=0.35.0, source=github.com/terraform-linters/tflint-ruleset-aws
09:34:58 config.go:358: [DEBUG]     terraform: enabled=true, version=, source=
09:34:58 option.go:77: [DEBUG] CLI Options
09:34:58 option.go:78: [DEBUG]   CallModuleType: local
09:34:58 option.go:79: [DEBUG]   Force: false
09:34:58 option.go:80: [DEBUG]   Format: 
09:34:58 option.go:81: [DEBUG]   Varfiles: 
09:34:58 option.go:82: [DEBUG]   Variables: 
09:34:58 option.go:83: [DEBUG]   EnableRules: 
09:34:58 option.go:84: [DEBUG]   DisableRules: 
09:34:58 option.go:85: [DEBUG]   Only: 
09:34:58 option.go:86: [DEBUG]   EnablePlugins: 
09:34:58 option.go:87: [DEBUG]   IgnoreModules:
09:34:58 loader.go:39: [INFO] Initialize new loader
09:34:58 module_mgr.go:63: [INFO] Module manifest file found. Initializing...
09:34:58 loader.go:78: [INFO] Building the root module while calling child modules...
09:34:58 loader.go:108: [DEBUG] Trying to load the local module: name=my_ecr_repository dir=modules/custom_ecr
09:34:58 runner.go:46: [INFO] Initialize new runner for root
09:34:58 runner.go:46: [INFO] Initialize new runner for module.my_ecr_repository
09:34:58 discovery.go:33: [INFO] Plugin "terraform" is not installed, but the bundled plugin is available.
09:34:58 discovery.go:54: [INFO] Plugin "terraform" found
09:34:58 [DEBUG] cmdrunner/cmd_runner.go:73: starting plugin: path=/usr/local/bin/tflint args=["/usr/local/bin/tflint", "--act-as-bundled-plugin"]
09:34:58 [DEBUG] cmdrunner/cmd_runner.go:80: plugin started: path=/usr/local/bin/tflint pid=38028
09:34:58 [DEBUG] go-plugin@v1.6.2/client.go:827: waiting for RPC address: plugin=/usr/local/bin/tflint
09:34:58 [DEBUG] go-plugin@v1.6.2/client.go:1216: tflint: 09:34:58 [DEBUG] go-plugin@v1.6.2/server.go:419: plugin address: network=unix address=/tmp/plugin2381623722
09:34:58 [DEBUG] go-plugin@v1.6.2/client.go:880: using plugin: version=11
09:34:58 discovery.go:90: [DEBUG] Find plugin path: .tflint.d/plugins/github.com/terraform-linters/tflint-ruleset-aws/0.35.0/tflint-ruleset-aws
09:34:58 discovery.go:54: [INFO] Plugin "aws" found
09:34:58 [DEBUG] cmdrunner/cmd_runner.go:73: starting plugin: path=.tflint.d/plugins/github.com/terraform-linters/tflint-ruleset-aws/0.35.0/tflint-ruleset-aws args=[".tflint.d/plugins/github.com/terraform-linters/tflint-ruleset-aws/0.35.0/tflint-ruleset-aws"]
09:34:58 [DEBUG] cmdrunner/cmd_runner.go:80: plugin started: path=.tflint.d/plugins/github.com/terraform-linters/tflint-ruleset-aws/0.35.0/tflint-ruleset-aws pid=38038
09:34:58 [DEBUG] go-plugin@v1.6.2/client.go:827: waiting for RPC address: plugin=.tflint.d/plugins/github.com/terraform-linters/tflint-ruleset-aws/0.35.0/tflint-ruleset-aws
09:34:58 [DEBUG] go-plugin@v1.6.2/client.go:880: using plugin: version=11
09:34:58 [DEBUG] go-plugin@v1.6.2/client.go:1216: tflint-ruleset-aws: 09:34:58 [DEBUG] go-plugin@v1.6.1/server.go:419: plugin address: network=unix address=/tmp/plugin1597952239
09:34:58 [DEBUG] host2plugin/client.go:124: starting host-side gRPC server
09:34:58 [DEBUG] host2plugin/client.go:124: starting host-side gRPC server
09:34:58 [DEBUG] host2plugin/client.go:124: starting host-side gRPC server
09:34:58 [DEBUG] host2plugin/client.go:124: starting host-side gRPC server
09:34:58 [DEBUG] go-plugin@v1.6.2/grpc_stdio.go:142: stdio: received EOF, stopping recv loop: err="rpc error: code = Unavailable desc = error reading from server: EOF"
09:34:58 [INFO]  go-plugin@v1.6.2/client.go:780: plugin process exited: plugin=/usr/local/bin/tflint id=38028
09:34:58 [DEBUG] go-plugin@v1.6.2/client.go:558: plugin exited
09:34:58 [DEBUG] go-plugin@v1.6.2/grpc_stdio.go:142: stdio: received EOF, stopping recv loop: err="rpc error: code = Unavailable desc = error reading from server: EOF"
09:34:58 [INFO]  go-plugin@v1.6.2/client.go:780: plugin process exited: plugin=.tflint.d/plugins/github.com/terraform-linters/tflint-ruleset-aws/0.35.0/tflint-ruleset-aws id=38038
09:34:58 [DEBUG] go-plugin@v1.6.2/client.go:558: plugin exited
2 issue(s) found:

Error: "%%!"(MISSING) does not match valid pattern ^(?:[a-z0-9]+(?:[._-][a-z0-9]+)*/)*[a-z0-9]+(?:[._-][a-z0-9]+)*$ (aws_ecr_repository_invalid_name)

  on main.tf line 13:
  13:   ecr_name = "%%%"  # Invalid ECR repository name

Callers:
   main.tf:13,14-19
   modules/custom_ecr/main.tf:9,10-22

Error: "%%!h(MISSING)ello-world" does not match valid pattern ^(?:[a-z0-9]+(?:[._-][a-z0-9]+)*/)*[a-z0-9]+(?:[._-][a-z0-9]+)*$ (aws_ecr_repository_invalid_name)

  on main.tf line 13:
  13:   ecr_name = "%%%"  # Invalid ECR repository name

Callers:
   main.tf:13,14-19
   modules/custom_ecr/main.tf:14,10-39

TFLint Version

0.54.0

Terraform Version

No response

Operating System

• Linux
• macOS
• Windows

[wata727]

Thank you for reporting this. This seems to be a bug that occurred when local values ​​were supported.

Whether an issue in a child module (./modules/custom_ecr) is related to the module's input values (ecr_name) ​​is determined by whether the range of the reported expression includes the corresponding var.ecr_name variable.
https://github.com/terraform-linters/tflint/blob/v0.54.0/tflint/runner.go#L239

To fix this, we would need to check the local value in the expression to determine if it contains var.ecr_name. For that matter, perhaps similar bugs exist with count.*, each.*, dynamic blocks.

While it is possible to fix this bug in the short term, the inspection model for child modules makes excessive assumptions, so a redesign of the model as in terraform-linters/tflint-plugin-sdk#193 may be more effective.