Consider mapping for use with associated_external_type

[bendbennett]

Currently, the generation of To<...>()/From<...>() methods (refer to Consider handling of associated_external_type for all types) uses a direct mapping from the Terraform Plugin Framework types to the API SDK types.

For example, usage of associated_external_type in the following specification results in the generation of the To<...>()/From<...>() methods.

{
  "datasources": [
    {
      "name": "example",
      "schema": {
        "attributes": [
          {
            "name": "list_nested_attribute",
            "list_nested": {
              "nested_object": {
                "associated_external_type": {
                  "import": {
                    "path": "example.com/apisdk"
                  },
                  "type": "*apisdk.Type"
                },
                "attributes": [
                  {
                    "name": "int64_attribute",
                    "int64": {
                      "computed_optional_required": "optional"
                    }
                  }
                ]
              },
              "computed_optional_required": "optional"
            }
          }
        ]
      }
    }
  ],
  "provider": {
    "name": "example"
  }
}

func (v ListNestedAttributeValue) ToApisdkType(ctx context.Context) (*apisdk.Type, diag.Diagnostics) {
	var diags diag.Diagnostics

	if v.IsNull() {
		return nil, diags
	}

	if v.IsUnknown() {
		diags.Append(diag.NewErrorDiagnostic(
			"ListNestedAttributeValue Value Is Unknown",
			`"ListNestedAttributeValue" is unknown.`,
		))

		return nil, diags
	}

	return &apisdk.Type{
		Int64Attribute: v.Int64Attribute.ValueInt64Pointer(),
	}, diags
}

func (v ListNestedAttributeValue) FromApisdkType(ctx context.Context, apiObject *apisdk.Type) (ListNestedAttributeValue, diag.Diagnostics) {
	var diags diag.Diagnostics

	if apiObject == nil {
		return NewListNestedAttributeValueNull(), diags
	}

	return ListNestedAttributeValue{
		Int64Attribute: types.Int64PointerValue(apiObject.Int64Attribute),
		state:          attr.ValueStateKnown,
	}, diags
}

The following assumptions are made during the generation of the To<...>()/From<...>() methods based on the specified associated_external_type:

• The API SDK type is a struct with fields which are named with the camel-cased attribute name (i.e., int64_attribute => Int64Attribute).
• The values held within the API SDK type are pointer values of the attribute value (i.e., int64 => *int64).

Proposal

Additional flexibility could be introduced by allowing the specification of "mapping" between the Terraform Plugin Framework types and the types specified by associated_external_type. This would increase the usefulness of the generated To<...>()/From<...>() methods and accommodate cases where a direct 1-2-1 mapping between the Terraform Plugin Framework types and the API SDK types was not present.