fly_machine.mounts.volume should only accept fly_volume.id, not fly_volume.name

[oscarhermoso]

Currently, the terraform docs state that the volume name can be used to identify the volume for the fly_machine. While this is partially true (resource is created on fly.io), it leaves terraform in a broken state.

https://registry.terraform.io/providers/fly-apps/fly/latest/docs/resources/machine

volume (String) Name or ID of volume

Steps to reproduce:

Define as follows:

mounts = [{
    volume = fly_volume.app.name
    path   = "/data"
  }]

Result

Terraform used the selected providers to generate the following execution plan. Resource actions are indicated with the following
symbols:
  ~ update in-place

Terraform will perform the following actions:

# module.redis.fly_machine.app["syd"] will be updated in-place
  ~ resource "fly_machine" "app" {
      ~ cputype   = "shared" -> (known after apply)
      ~ id        = "*************" -> (known after apply)
      ~ mounts    = [
          ~ {
              ~ encrypted = true -> (known after apply)
              ~ size_gb   = 1 -> (known after apply)
              ~ volume    = "vol_2yxp4mnk2z3r63qd" -> "org_app_dev_syd"
                # (1 unchanged attribute hidden)
            },
        ]
        name      = "org-app-dev-syd"
      ~ privateip = ""*************" -> (known after apply)
        # (6 unchanged attributes hidden)
    }

Plan: 0 to add, 1 to change, 0 to destroy.

Do you want to perform these actions?
  Terraform will perform the actions described above.
  Only 'yes' will be accepted to approve.

  Enter a value: yes

Error: Provider produced inconsistent result after apply
│ When applying changes to module.redis.fly_machine.app["syd"], provider "provider[\"registry.terraform.io/fly-apps/fly\"]" produced an
│ unexpected new value: .mounts[0].volume: was cty.StringVal("org_app_dev_syd"), but now cty.StringVal("vol_2yxp4mnk2z3r63qd").
│ 
│ This is a bug in the provider, which should be reported in the provider's own issue tracker.

Workaround/resolution

• terraform destroy and then
• Define as follows:

mounts = [{
    volume = fly_volume.app.id  // <!-- specify .id instead of .name
    path   = "/data"
  }]

• terraform apply

Ideally the docs (and possibly the code) are updated to reflect that the fly_volume id should be used instead of name for mounts.