How to render terraform data when using a count - terraform

Question

I was using a count for creating multiple AWS task_definitions that should be executed by an AWS step function.
The task_definition required a data "template_file" "task_definition" { section to be able to fill the template data.
Then I needed to render the template data for multiple definitions at a time and I was blocked by an error looking like this:
The "count" value depends on resource attributes that cannot be determined until apply, so Terraform cannot predict how many instances will be created. To work around this, use the -target argument to first apply only the resources that the for_each depends on.
Here's the initial code:
data "template_file" "task_definition" {
count = length(var.task_container_command)
template = file("./configs/file.json")
vars = {
task = module.ecs[count.index].task_definition
}
}
module "step_function" {
count = length(var.task_container_command)
source = "path"
region = var.region
name = "${var.step_function_name}-${count.index}"
definition_file = data.template_file.task_definition.rendered
}
The point here is that I can't render task_definition because these are not known by terraform yet before the apply. I wasn't able to use the -target argument either because I wanted to make the change in code and not in my deployment pipeline. Meaning when you try to do a terraform plan on the definition_file, the error will pop up.
Solution is below.

Answer 1

What worked was to decouple the use of the count from the .rendered argument by doing this:
data "template_file" "task_definition" {
count = length(var.task_container_command)
template = file("./configs/file.json")
vars = {
task = module.ecs[count.index].task_definition
}
}
resource "local_file" "foo" {
count = length(var.task_container_command)
content = element(data.template_file.task_definition.*.rendered, count.index)
filename = "task-definition-${count.index}"
}
module "step_function" {
count = length(var.task_container_command)
source = "path"
region = var.region
name = "${var.step_function_name}-${count.index}"
definition_file = local_file.foo[count.index].filename
}
Now your data is rendered in the resource called "foo" here and then passed to the step_function module so the terraform plan already knows what's inside your variable. The content element of foo acts like a loop to render each task_definition that I've created using a different filename to avoid duplicates.
Hope this helped :)