Nested validation issues with non-defaulted nested parameters

[Steven Hardy]

There are a couple of related problems with nested validation which are causing us some issues with TripleO atm:

$ cat parent.yaml
heat_template_version: 2016-10-14

parameters:
  with_default:
    type: string
    default: foo
  no_default:
    type: string

resources:

  a_resource:
    type: OS::Heat::RandomString

  the_nested:
    type: nested.yaml
    properties:
      from_parent_param: {get_param: no_default}
      from_parent_param_default: {get_param: with_default}
      from_parent_attr: {get_attr: [a_resource, value]}
[stack@instack ~]$ cat nested.yaml
heat_template_version: 2016-04-08

parameters:
  from_parent_param:
    type: string
  from_parent_param_default:
    type: string
  from_parent_attr:
    type: string

resources:
  test:
    type: OS::Heat::RandomString
    properties:
      salt:
        list_join:
          - ','
          - {get_param: from_parent_param}
          - {get_param: from_parent_param_default}
          - {get_param: from_parent_attr}

$ heat template-validate -f parent.yaml --show-nested
WARNING (shell) "heat template-validate" is deprecated, please use "openstack orchestration template validate" instead
{
  "NestedParameters": {
    "the_nested": {
      "Type": "file:///home/stack/nested.yaml",
      "Description": "No description",
      "Parameters": {
        "from_parent_param": {
          "Type": "String",
          "NoEcho": "false",
          "Description": "",
          "Label": "from_parent_param"
        },
        "from_parent_param_default": {
          "Type": "String",
          "NoEcho": "false",
          "Description": "",
          "Value": "foo",
          "Label": "from_parent_param_default"
        },
        "from_parent_attr": {
          "Type": "String",
          "NoEcho": "false",
          "Description": "",
          "Label": "from_parent_attr"
        }
      }
    }
  },
  "Description": "No description",
  "Parameters": {
    "no_default": {
      "Type": "String",
      "NoEcho": "false",
      "Description": "",
      "Label": "no_default"
    },
    "with_default": {
      "Default": "foo",
      "Type": "String",
      "NoEcho": "false",
      "Description": "",
      "Label": "with_default"
    }
  }
}

The problem here is that there is no way to know that a Value is actually passed from the parent, e.g for from_parent_param and from_parent_attr, we know there should be some Value on create, so a placeholder is needed (to distinguish from parameters in nested.yaml where no default is defined *and* no value is passed from the parent.

[Thomas Herve (therve)]

It took some more explanations for me to understand, so I'll try to write them down here: the problem is that we'd like the Value field to have something indication that the parent passes down something, presumably a placeholder.

It's a good bug to track, but I suspect that would be solve by a larger spec involving validation. We need at least to agree on what the Value field would look like in that case.