Support computed values in TypeSet

[mavogel]

Currently Computed within lists work but no in sets. Each time they give a dirty plan due to the hash change.

Steps to reproduce are in the branch: https://github.com/terraform-providers/terraform-provider-docker/tree/investigate-type-set-list-fail

[gdavison]

I've confirmed that this same error occurs when updating a TypeSet with TypeString elements, so it likely affects TypeSet in general.

We're encountering the error when updating an aws_elasticache_replication_group (hashicorp/terraform-provider-aws#17161). Creation works as expected, and a subsequent refresh will correct state.

[gdavison]

As pointed out in hashicorp/terraform-provider-aws#17161 (comment), this needs a CustomizeDiff function with a call to diff.SetNewComputed()

[smaeda-ks]

Hi @gdavison and @bflad,

I was looking at your comment: hashicorp/terraform-provider-aws#17161 (comment) as we're also facing the same issue in our provider, which we're trying to fix.

One thing I wanted to get your confirmation is that, is this the case only for TypeSet computed attributes? I've been testing this but looks like other schema types computed attributes are being updated correctly upon an update action, but not TypeSet.

The above comment, as well as this community post, was giving me the impression that it's a generic limitation for all computed attributes regardless of the schema types. So just wanted to clarify that before implementing the fix using d.SetNewComputed().

Thanks in advance