Function setproduct() panics with empty sets/lists

[peikk0]

Terraform Version

Terraform v0.15.1
on darwin_amd64

Terraform Configuration Files

output "panics" {
  value = setproduct([], [])
}

output "panics_too" {
  value = setproduct(["a", "b"], [])
}

output "panics_again" {
  value = setproduct([], ["c", "d"])
}

output "does_not_panic" {
  value = setproduct(["a", "b"], ["c", "d"])
}

Debug Output

https://gist.github.com/peikk0/813a660c334fef294db7b12557be9048#file-debug-log

Crash Output

https://gist.github.com/peikk0/813a660c334fef294db7b12557be9048#file-crash-log

Expected Behavior

setproduct() should not panic with empty lists or sets.

Actual Behavior

setproduct() panics with empty lists or sets.

Steps to Reproduce

1. terraform init
2. terraform apply

Additional Context

References

[mantoine96]

I've encountered the same issue. It seems to be a regression between 0.15.0 and 0.15.1, as using 0.15.0 works as expected. I believe it is linked to: c0328e4

Confirmed via git bisect:

c0328e414accdd90f73f9ff17e8380f2cf67b4b9 is the first bad commit
commit c0328e414accdd90f73f9ff17e8380f2cf67b4b9
Author: The Terraform Team <52939924+teamterraform@users.noreply.github.com>
Date:   Wed Apr 21 10:11:36 2021 -0700

    dependencies: update cty from v1.8.1 to v1.8.2

    This includes the improvements to various collection-related functions to
    make them handle marks more precisely. For Terraform in particular that
    translates into handling sensitivity more precisely, so that non-sensitive
    collections that happen to contain sensitive elements won't get simplified
    into wholly-sensitive collections when using these functions.

 go.mod | 2 +-
 go.sum | 2 ++
 2 files changed, 3 insertions(+), 1 deletion(-)
bisect run success

I have opened an issue and a PR on go-cty:

• function/stdlib: The setproduct function panics when an argument is an empty list zclconf/go-cty#102
• Fix panic in setproduct when one of the arguments is an empty list zclconf/go-cty#103

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