Allow "generic" use of State.GetAttribute

[ewbankkit]

Module version

v0.5.0

Use-cases

The changes made in #167 prevent the "generic" use of State.GetAttribute to be used to copy a value, for example:

https://github.com/hashicorp/terraform-provider-awscc/blob/3cdc5b061801143a621f3d571c53e0e36b22ab96/internal/generic/state.go#L12-L26

// CopyValueAtPath copies the value at a specified path from source State to destination State.
func CopyValueAtPath(ctx context.Context, dst, src *tfsdk.State, path *tftypes.AttributePath) error {
	val, diags := src.GetAttribute(ctx, path)

	if diags.HasError() {
		return tfresource.DiagsError(diags)
	}

	diags = dst.SetAttribute(ctx, path, val)

	if diags.HasError() {
		return tfresource.DiagsError(diags)
	}

	return nil
}

I have tried using a pointer to attr.Value:

func CopyValueAtPath(ctx context.Context, dst, src *tfsdk.State, path *tftypes.AttributePath) error {
	var val attr.Value
	diags := src.GetAttribute(ctx, path, &val)

	if diags.HasError() {
		return tfresource.DiagsError(diags)
	}

	diags = dst.SetAttribute(ctx, path, val)

	if diags.HasError() {
		return tfresource.DiagsError(diags)
	}

	return nil
}

but this fails:

    state_test.go:471: unexpected error from CopyValueAtPath: 1 error occurred:
        	* An unexpected error was encountered trying to convert into a Terraform value. This is always an error in the provider. Please report the following to the provider developer:
        
        Cannot use attr.Value attr.Value, only types.Number is supported because types.primitive is the type in the schema

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