PlanResourceChange Always Showing Differences

[bflad]

Module version

cf6f24087d3af45f583d0736c6ed841243d23653 (post v0.4.1, pre v0.4.2)

Relevant provider source code

Any schema with Computed only attributes. For example, hashicups-pf:

func (r resourceOrderType) GetSchema(_ context.Context) (tfsdk.Schema, diag.Diagnostics) {
	return tfsdk.Schema{
		Attributes: map[string]tfsdk.Attribute{
			"id": {
				Type: types.StringType,
				// When Computed is true, the provider will set value --
				// the user cannot define the value
				Computed: true,
			},
			"last_updated": {
				Type:     types.StringType,
				Computed: true,
			},
			"items": {
				// If Required is true, Terraform will throw error if user
				// doesn't specify value
				// If Optional is true, user can choose to supply a value
				Required: true,
				Attributes: tfsdk.ListNestedAttributes(map[string]tfsdk.Attribute{
					"quantity": {
						Type:     types.NumberType,
						Required: true,
					},
					"coffee": {
						Required: true,
						Attributes: tfsdk.SingleNestedAttributes(map[string]tfsdk.Attribute{
							"id": {
								Type:     types.NumberType,
								Required: true,
							},
							"name": {
								Type:     types.StringType,
								Computed: true,
							},
							"teaser": {
								Type:     types.StringType,
								Computed: true,
							},
							"description": {
								Type:     types.StringType,
								Computed: true,
							},
							"price": {
								Type:     types.NumberType,
								Computed: true,
							},
							"image": {
								Type:     types.StringType,
								Computed: true,
							},
						}),
					},
				}, tfsdk.ListNestedAttributesOptions{}),
			},
		},
	}, nil
}

Terraform Configuration Files

resource "hashicups_order" "edu" {
  items = [{
    coffee = {
      id = 3
    }
    quantity = 2
    }, {
    coffee = {
      id = 1
    }
    quantity = 2
    }
  ]
}

Expected Behavior

With no configuration changes (e.g. v0.4.1 behavior):

hashicups_order.edu: Refreshing state... [id=1]

No changes. Your infrastructure matches the configuration.

Actual Behavior

With no configuration changes:

$ terraform apply
...
hashicups_order.edu: Refreshing state... [id=1]

Terraform used the selected providers to generate the following execution plan. Resource actions are indicated with the following symbols:
  ~ update in-place

Terraform will perform the following actions:

  # hashicups_order.edu will be updated in-place
  ~ resource "hashicups_order" "edu" {
      ~ id           = "1" -> (known after apply)
      ~ items        = [
          ~ {
            ~ coffee   = {
              + description = (known after apply)
                id          = 3
              ~ image       = "/nomad.png" -> (known after apply)
              ~ name        = "Nomadicano" -> (known after apply)
              ~ price       = 150 -> (known after apply)
              ~ teaser      = "Drink one today and you will want to schedule another" -> (known after apply)
            }
              # (1 unchanged attribute hidden)

            ~ coffee   = {
              + description = (known after apply)
                id          = 1
              ~ image       = "/packer.png" -> (known after apply)
              ~ name        = "Packer Spiced Latte" -> (known after apply)
              ~ price       = 350 -> (known after apply)
              ~ teaser      = "Packed with goodness to spice up your images" -> (known after apply)
            }
              # (2 unchanged attributes hidden)
          },
        ]
      ~ last_updated = "Tuesday, 28-Sep-21 11:53:27 EDT" -> (known after apply)
    }

Plan: 0 to add, 1 to change, 0 to destroy.

Steps to Reproduce

1. terraform apply
2. terraform apply (with no configuration changes)

References

• Can't update Computed fields #175
• Fix planning. #176

[bflad]

The behavior added in #176 is on the right path, marking Computed only attributes as unknown during plan, however this behavior should only occur when there are configuration changes. This is further complicated that attribute and resource plan modifiers may introduce plan changes that should trigger the behavior. This may result in a two-phase approach, not sure.

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