Error: Reference to undeclared resource

 terraform plan
╷
│ Error: Reference to undeclared resource
│
│   on main.tf line 9, in resource "aws_instance" "example":
│    9:   ami               = data.aws_ami.windows.id
│
│ A data resource "aws_ami" "windows" has not been declared in the root module.

See also

• terraform plan: [ -refresh-only | -lock=false | -target | -var-file | will be created | --help], Terraform plan errors, Terraform plan examples, Terraform plan execution errors, (known after apply)