attr: Add ValueFromFramework and ToFrameworkValue Interface Functions to attr.Value

[bendbennett]

Module version

github.com/hashicorp/terraform-plugin-framework v0.15.0

Use-cases

A first step required for making the use of custom types for nested attributes feasible requires a mechanism for converting to/from the framework type (e.g., types.List).

Attempted Solutions

Using an interface implemented by custom types that is specific to the framework type (e.g., types.List) that they embed and then using type assertion to determine if the type being used is either a framework type (e.g., types.List) or a type that implements an interface that gives access to the framework type (e.g., types.List) embedded in the custom type.

Proposal

Introduce separate interfaces for each of the framework types that can be implemented by custom types to allow access to the embedded type and to obtain an instance of the custom type by passing the framework type.

package attr

type ListType interface {
  attr.Type // common bits

  ValueFromFramework(context.Context, types.List) (Value, diag.Diagnostics)
}

type ListValue interface {
  attr.Value

  ToFrameworkValue(context.Context) (types.List, diag.Diagnostics)
}

Once these interfaces are in place then custom types that embed framework types (e.g., types.List) can be created and used in place of framework types.

References

• Consider Allowing Usage of Custom Types for Nested Attributes #532

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