ConflictsWith should flag a violation only if the field has a non zero value set. about terraform-plugin-sdk HOT 3 CLOSED

Hi @rosbo!

The configuration language revamp that is underway will introduce a proper idea of "unset" as separate from zero-value, and introduce null as an expression that can be assigned to express "unset", which I think will eventually get us to a place where we can robustly implement this sort of conditional attribute assignment.

# NOT YET IMPLEMENTED; may change before release

resource "google_project" "host" {
  name            = "${var.project_name}"
  org_id          = "${var.org_id != "" ? var.org_id : null}"
  folder_id       = "${var.folder_id != "" ? var.folder_id : null}"
  project_id      = "${var.project_id == "" ? random_id.default-project-id.hex : var.project_id}"
  billing_account = "${var.billing_account}"
}

For now there may be another way to achieve this goal for this resource in particular. In 0.11.0-beta1 we introduced CustomizeDiff as a new function a resource can implement, which gives it the opportunity to inspect the diff, reject certain combinations of changes, and add additional information. In principle this could be used to introduce some custom validation behavior here instead of using ConflictsWith. For example:

func projectCustomizeDiff(d *ResourceDiff, meta interface{}) error {
    orgId := d.Get("org_id")
    folderId := d.Get("folder_id")
    if orgId != "" && folderId != "" {
        return errors.New("org_id and folder_id arguments cannot both be set")
    }
    return nil
}

So far this function is only available in the beta, so it may be worth waiting until we reach 0.11.0 final before updating providers to vendor the new version, in case there are some bugs that need to be dealt with. In principle this function can replace quite a lot of the declarative validations we currently support on schemas, though I'd suggest using it sparingly since the declarative validation rules do, at least, help ensure more consistency between the behaviors of resources.

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Since this issue was raised, the Terraform configuration language in CLI version 0.12 and later has implemented support for null values. When this value is used in the context of configuring an attribute, Terraform will treat the attribute as if it was not set in the configuration at all. Using this style of (non 😄 ) configuration allows ConflictsWith to work as expected.

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