# Plan Modification

## Custom Attribute Plan Modification

Attribute plan modifiers enable advanced default value, resource replacement, and difference suppression logic in managed resources. Due to the Terraform SDK implementation, attribute-level plan modifiers do not have access to provider-level configuration or the API client, however that SDK does support custom resource-level plan modification with implementing the [`resource.ResourceWithModifyPlan` interface](https://pkg.go.dev/github.com/hashicorp/terraform-plugin-framework/resource#ResourceWithModifyPlan).

Use the `x-speakeasy-plan-modifiers` extension to add custom attribute-level plan modification logic to Terraform plan operations.

```yaml
components:
  schemas:
    Pet:
      type: object
      x-speakeasy-entity: Pet
      properties:
        name:
          type: string
        age:
          type: integer
          x-speakeasy-plan-modifiers: AgeModifier
```

<Callout title="Note" type="info">
  Once you've added the `x-speakeasy-plan-modifiers` extension with a modifier, Speakeasy's next Terraform provider generation will bootstrap a custom plan modifier file. Using the previous YAML snippet as an example, the modifier will be located at `internal/planmodifiers/int64planmodifier/age_modifier.go`, and import the schema configuration wherever `x-speakeasy-plan-modifiers: AgeModifier` is referenced.
</Callout>

The `x-speakeasy-plan-modifiers` extension supports an array of names as well, such as:

```yaml
x-speakeasy-plan-modifiers:
  - FirstPlanModifier
  - SecondPlanModifier
```

### Implementation Notes

A plan modifier is a type that implements the plan modifier interface defined by the `terraform-plugin-framework`. A unique plan modifier is bootstrapped in the appropriate subfolder for the Terraform type that it is applied to, which is usually one of the following:

- `boolplanmodifiers`
- `float64planmodifiers`
- `int64planmodifiers`
- `listplanmodifiers`
- `mapplanmodifiers`
- `numberplanmodifiers`
- `objectplanmodifiers`
- `setplanmodifiers`
- `stringplanmodifiers`

4. A modifier can only be applied to a resource attribute. The annotation will be ignored for data sources. Modifiers cannot be applied at the same level as the `x-speakeasy-entity` annotation because that becomes the "root" of the Terraform resource.

5. Speakeasy regenerations do not delete user-written code. If the modifier is no longer in use, it will be ignored (no longer referenced) but the source file will remain. You might want to delete such an orphaned modifier file for repository hygiene.