New Check: Avoid Unstable (*helper/schema.ResourceData).SetId() Call Expressions with time.Now()

[bflad]

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Description

Terraform 0.13.0 is currently exhibiting behavior where data sources are showing up in plans more often. One common issue with this plan output is that it appears to be caused by the data source ID attribute changing, which may or may not be the actual cause for the new plan output. e.g.

$ terraform plan
Refreshing Terraform state in-memory prior to plan...
The refreshed state will be used to calculate this plan, but will not be
persisted to local or remote state storage.

data.aws_availability_zones.a: Refreshing state... [id=2020-08-11 20:23:09.61125009 +0000 UTC]

------------------------------------------------------------------------

An execution plan has been generated and is shown below.
Resource actions are indicated with the following symbols:
 <= read (data resources)

Terraform will perform the following actions:

  # data.aws_availability_zones.a will be read during apply
  # (config refers to values not yet known)
 <= data "aws_availability_zones" "a"  {
        group_names = [
            "us-west-2",
            "us-west-2-lax-1",
        ]
      ~ id          = "2020-08-11 20:23:19.963587604 +0000 UTC" -> "2020-08-11 20:23:21.360002629 +0000 UTC"
        names       = [
            "us-west-2-lax-1a",
            "us-west-2a",
            "us-west-2b",
            "us-west-2c",
            "us-west-2d",
        ]
        zone_ids    = [
            "usw2-lax1-az1",
            "usw2-az1",
            "usw2-az2",
            "usw2-az3",
            "usw2-az4",
        ]
    }

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

The core team developers have confirmed that this will eventually be the behavior for data source handling in the future, so this check is twofold: to catch common problems now and to prevent them in the future.

New Checks(s)

• R016

Flagged Provider Code

d.SetId(time.Now().Format(time.RFC3339))

Passing Provider Code

d.SetId(/* some stable value */)

References

• 0.13.0 - Is it possible to suppress or hide the "will be read during apply" messages for data resources?  hashicorp/terraform#25805
• Data sources with non-deterministic IDs show perpetual diff with Terraform 0.13 (R015, R016, R017 linters) hashicorp/terraform-provider-aws#14579