Write-only dynamic attribute causes plan diff everytime #1096
Description
Module version
ecd80f67daed
Relevant provider source code
...Terraform Configuration Files
terraform {
required_providers {
restful = {
source = "magodo/restful"
}
}
}
provider "restful" {
base_url = "http://local:3000"
}
variable "foo" {
type = string
ephemeral = true
default = null
}
resource "restful_resource" "test" {
path = "/resources"
read_path = "/resources/$(body.id)"
body = {
foo = "bar"
}
ephemeral_body = {
bar = var.foo
}
}Debug Output
After the initial successful apply, any further plan will cause diff:
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:
# restful_resource.test will be updated in-place
~ resource "restful_resource" "test" {
id = "/resources/2"
~ output = {
- foo = "bar"
- id = 2
} -> (known after apply)
# (4 unchanged attributes hidden)
}
Plan: 0 to add, 1 to change, 0 to destroy.Expected Behavior
If I understand the document correctly:
Write-only argument values cannot produce a Terraform plan difference.
This is because the prior state value for a write-only argument will always be null and the planned/final state value will also be null, therefore, it cannot produce a diff on its own.
Even if the ephemeral input variable got changed, the plan shall also show no diff as long as other non write-only attributes are not changed.
Actual Behavior
After the initial successful apply, any further plan will cause diff.
Steps to Reproduce
Use the branch https://github.com/magodo/terraform-provider-restful/tree/ephemeral_body to build and use the provider locally.
References
Note that the output attribute is Dynamic type. I've also tried to generate the plan output, which is like below:
{
"format_version": "1.2",
"terraform_version": "1.12.0-dev",
"variables": {
"foo": {
"value": null
}
},
"planned_values": {
"root_module": {
"resources": [
{
"address": "restful_resource.test",
"mode": "managed",
"type": "restful_resource",
"name": "test",
"provider_name": "registry.terraform.io/magodo/restful",
"schema_version": 2,
"values": {
"body": {
"foo": "bar"
},
"check_existance": null,
"create_header": null,
"create_method": null,
"create_query": null,
"create_selector": null,
"delete_body": null,
"delete_header": null,
"delete_method": null,
"delete_path": null,
"delete_query": null,
"ephemeral_body": null,
"force_new_attrs": null,
"header": null,
"id": "/resources/1",
"merge_patch_disabled": null,
"output_attrs": null,
"path": "/resources",
"poll_create": null,
"poll_delete": null,
"poll_update": null,
"precheck_create": null,
"precheck_delete": null,
"precheck_update": null,
"query": null,
"read_header": null,
"read_path": "/resources/$(body.id)",
"read_query": null,
"read_response_template": null,
"read_selector": null,
"update_body_patches": null,
"update_header": null,
"update_method": null,
"update_path": null,
"update_query": null,
"write_only_attrs": null
},
"sensitive_values": {
"body": {}
}
}
]
}
},
"resource_changes": [
{
"address": "restful_resource.test",
"mode": "managed",
"type": "restful_resource",
"name": "test",
"provider_name": "registry.terraform.io/magodo/restful",
"change": {
"actions": [
"update"
],
"before": {
"body": {
"foo": "bar"
},
"check_existance": null,
"create_header": null,
"create_method": null,
"create_query": null,
"create_selector": null,
"delete_body": null,
"delete_header": null,
"delete_method": null,
"delete_path": null,
"delete_query": null,
"ephemeral_body": null,
"force_new_attrs": null,
"header": null,
"id": "/resources/1",
"merge_patch_disabled": null,
"output": {
"bar": "baz",
"foo": "bar",
"id": 1
},
"output_attrs": null,
"path": "/resources",
"poll_create": null,
"poll_delete": null,
"poll_update": null,
"precheck_create": null,
"precheck_delete": null,
"precheck_update": null,
"query": null,
"read_header": null,
"read_path": "/resources/$(body.id)",
"read_query": null,
"read_response_template": null,
"read_selector": null,
"update_body_patches": null,
"update_header": null,
"update_method": null,
"update_path": null,
"update_query": null,
"write_only_attrs": null
},
"after": {
"body": {
"foo": "bar"
},
"check_existance": null,
"create_header": null,
"create_method": null,
"create_query": null,
"create_selector": null,
"delete_body": null,
"delete_header": null,
"delete_method": null,
"delete_path": null,
"delete_query": null,
"ephemeral_body": null,
"force_new_attrs": null,
"header": null,
"id": "/resources/1",
"merge_patch_disabled": null,
"output_attrs": null,
"path": "/resources",
"poll_create": null,
"poll_delete": null,
"poll_update": null,
"precheck_create": null,
"precheck_delete": null,
"precheck_update": null,
"query": null,
"read_header": null,
"read_path": "/resources/$(body.id)",
"read_query": null,
"read_response_template": null,
"read_selector": null,
"update_body_patches": null,
"update_header": null,
"update_method": null,
"update_path": null,
"update_query": null,
"write_only_attrs": null
},
"after_unknown": {
"body": {},
"output": true
},
"before_sensitive": {
"body": {},
"output": {}
},
"after_sensitive": {
"body": {}
}
}
}
],
"prior_state": {
"format_version": "1.0",
"terraform_version": "1.12.0",
"values": {
"root_module": {
"resources": [
{
"address": "restful_resource.test",
"mode": "managed",
"type": "restful_resource",
"name": "test",
"provider_name": "registry.terraform.io/magodo/restful",
"schema_version": 2,
"values": {
"body": {
"foo": "bar"
},
"check_existance": null,
"create_header": null,
"create_method": null,
"create_query": null,
"create_selector": null,
"delete_body": null,
"delete_header": null,
"delete_method": null,
"delete_path": null,
"delete_query": null,
"ephemeral_body": null,
"force_new_attrs": null,
"header": null,
"id": "/resources/1",
"merge_patch_disabled": null,
"output": {
"bar": "baz",
"foo": "bar",
"id": 1
},
"output_attrs": null,
"path": "/resources",
"poll_create": null,
"poll_delete": null,
"poll_update": null,
"precheck_create": null,
"precheck_delete": null,
"precheck_update": null,
"query": null,
"read_header": null,
"read_path": "/resources/$(body.id)",
"read_query": null,
"read_response_template": null,
"read_selector": null,
"update_body_patches": null,
"update_header": null,
"update_method": null,
"update_path": null,
"update_query": null,
"write_only_attrs": null
},
"sensitive_values": {
"body": {},
"output": {}
}
}
]
}
}
},
"configuration": {
"provider_config": {
"restful": {
"name": "restful",
"full_name": "registry.terraform.io/magodo/restful",
"expressions": {
"base_url": {
"constant_value": "http://local:3000"
}
}
}
},
"root_module": {
"resources": [
{
"address": "restful_resource.test",
"mode": "managed",
"type": "restful_resource",
"name": "test",
"provider_config_key": "restful",
"expressions": {
"body": {
"constant_value": {
"foo": "bar"
}
},
"ephemeral_body": {
"references": [
"var.foo"
]
},
"path": {
"constant_value": "/resources"
},
"read_path": {
"constant_value": "/resources/$(body.id)"
}
},
"schema_version": 2
}
],
"variables": {
"foo": {
"default": null
}
}
}
},
"timestamp": "2025-02-19T01:28:46Z",
"applyable": true,
"complete": true,
"errored": false
}