### Terraform Version ```shell Terraform v1.6.0 on linux_amd64 provider registry.terraform.io/hashicorp/aws v6.20.0 ``` ### Terraform Configuration Files terraform { required_version = ">= 1.6.0" required_providers { aws = { source = "hashicorp/aws" version = ">= 6.0.0" } } } provider "aws" { region = "us-east-1" } variable "use_default_bus" { type = bool default = true } # When true, data exists and resource count = 0 data "aws_cloudwatch_event_bus" "default" { count = var.use_default_bus ? 1 : 0 name = "default" } # When true, this resource does not exist (count = 0) resource "aws_cloudwatch_event_bus" "this" { count = var.use_default_bus ? 0 : 1 name = "example-bus" } locals { # Conditional references a possibly-nonexistent resource index on the else branch. # On Terraform 1.6.0 this can crash validate with cty marks error. event_bus_arn = var.use_default_bus ? data.aws_cloudwatch_event_bus.default[0].arn : aws_cloudwatch_event_bus.this[0].arn } output "event_bus_arn" { value = local.event_bus_arn } ### Debug Output !!!!!!!!!!!!!!!!!!!!!!!!!!! TERRAFORM CRASH !!!!!!!!!!!!!!!!!!!!!!!!!!!! value is marked, so must be unmarked first github.com/zclconf/go-cty/cty.Value.assertUnmarked(...) github.com/zclconf/go-cty/cty.Value.AsString(...) github.com/zclconf/go-cty/cty.Value.Range(...) github.com/hashicorp/hcl/v2/hclsyntax.(*ConditionalExpr).Value(...) github.com/hashicorp/terraform/internal/terraform.(*NodeValidatableResource).validateResource(...) ### Expected Behavior terraform validate should succeed or return a normal diagnostic; it should not crash. ### Actual Behavior terraform validate crashes with: “value is marked, so must be unmarked first” Stack trace shows hclsyntax.(*ConditionalExpr).Value and cty marks. ### Steps to Reproduce Save the configuration above as main.tf. Run: terraform init -input=false -upgrade terraform validate Crash reproduces consistently on Terraform 1.6.0. ### Additional Context Environment: CI runner (Ubuntu), Terraform 1.6.0, aws provider v6.20.0. The crash appears tied to a conditional expression that selects between a data source and a resource whose count = 0, referencing aws_cloudwatch_event_bus.this[0].arn on the else branch. Although conditionals should short-circuit, evaluating branch metadata seems to propagate cty marks and triggers the panic. ### References N/A (could not find an existing issue specifically for this exact crash; it resembles prior cty marks/conditional evaluation bugs) ### Generative AI / LLM assisted development? Cursor - ChatGPT-5