Invalid calculation result together with floor/ceil

[chris922]

We faced a strange bug that prevents us from upgrading from Terraform v0.15.4 to v1.0.3.
With v0.15.4 we can't reproduce the bug, with v1.0.3 we can. So the bug was introduced after v0.15.4.

EDIT: See my comment, bug seems to be there since v1.0.2

Imho it is a critical one as it leads to unexpected behavior for each apply.

Terraform Version

Terraform v1.0.3
on linux_amd64

Terraform Configuration Files

locals {
  val = 64 - 4

  val2 = floor(local.val)
}

output "val" {
  value = local.val
}

Expected Behavior

Output val should have the exact value 60.

Actual Behavior

Sometimes the output val has the value 60, sometimes it has a lot of decimals, e.g. 60.00000000000000000325260651745651330202235840260982513427734375

Steps to Reproduce

Call terraform apply -auto-approve multiple times, the output val will have different values.

If you remove the line val2 = floor(local.val) the output val will be stable. Thus it seems that the local val will somehow be changed when using floor (or ceil) on it.. I would expect the local is constant and can't be changed by some other expression.

You can also change val to val = 64 (remove the subtraction) and then it keeps stable. So substracting numbers and then using floor/ceil seems to make trouble.

[chris922]

I just downloaded TF v1.0.1 and v1.0.2 and the bug should be there since v1.0.2. With v1.0.1 everything seems to be fine.

[jbardin]

Thanks for the reproduction case @chris922!

Reported upstream in zclconf/go-cty#114

[chris922]

@jbardin : Thanks a lot for the fix. What is the usual approach with bugs in other libraries? As the PR was merged in go-cty project, will this dependency updated directly or is there a new go-cty release required? The last one was in 2020, so I don't know about the release train there.. hopefully it will not take a long time until they do a bugfix release.

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