Inconsistent operators precedence

[bpineau]

Hi,

Terraform Version

Terraform v0.7.4

Terraform Configuration Files

data "template_file" "example" {
  template = <<EOF

var1 = ${var1}
var2 = ${var2}
EOF

  vars {
    var1 = "${1 + 3 % 2}"
    var2 = "${3 % 2 + 1}"
  }
}

output "rendered" {
  value = "${data.template_file.example.rendered}"
}

Debug Output

rendered =
var1 = 0
var2 = 2

Expected Behavior

If "%" has precedence over "+", var1 should output "2"
If "+" has precedence over "%", var2 should output "0"

Actual Behavior

In the "1 + 3 % 2" case, the addition takes precedence (outputs 0).
In the "3 % 2 + 1" case, the modulo takes precedence (outputs 2)

Same thing with a simple division ("${2 + 2 / 2}" => 2 , "${2 / 2 + 2}" => 3).

As if the values were computed left to right, without precedence considerations ?
If that so, maybe should this be stated in the interpolation doc's "Math" section (since it could be counter-intuitive) ?

Steps to Reproduce

1. terraform apply

[rottenbytes]

upvote for this one. even if using parenthesis allows to force order, this is pretty annoying

[mitchellh]

The precedence isn't inconsistent, they're equal: + is equal to % currently. This is primarily due to legacy reasons and changing this now would actually likely break a large number of configurations.

We can mark this for 0.8 since it'll break configurations. :(

[rottenbytes]

Hi @mitchellh,

I had the behaviour with - and * operators.

Example : in var.myvar * 1024.0 - var.myvar * 1024.0 * 0.9 : I had to use parenthesis and come up with (var.myvar * 1024.0) - (var.myvar * 1024.0 * 0.9) to get the expected result.

I think inconsistent is used here to mark what is usually expected from mathematic operator precedence.

[mitchellh]

The expectation is fair and is why this issue is still open, but the fact is that this will still be a hugely backwards incompatible change and will likely break existing configs so we need to be careful about introducing it only in a major release, which we'll plan.

[rottenbytes]

I totally get that and understand not introducing breaking changes 🙇 Maybe add a hint in the docs as @bpineau stated ?

[mitchellh]

Thanks @rottenbytes for the docs hint. I'm going to close this for now since its an HIL bug that we have over there. We'll address this perhaps in 0.9. It is easy enough to do but I want to give people some warning/time before the switch. Thanks!

[ghost]

I'm going to lock this issue because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues.

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