hcl2template: don't use it's var type when the default value for a variable is empty

[azr]

In HCL, when no type is given for a var, the type of the default value will be used. But the type of default = {} is the EmptyObject.

Converting something in HCL to the EmptyObject or EmptyTuple types will return a new empty object. Meaning that if we try to set these later on, the result will remain something empty.

This potentially fixes #11551

• fix
• tests

[nywilken]

In theory I like the approach but I do wonder if the right thing to do here is error instead of trying EmptyObject and EmptyTuple as a non-type. I was curious how this would work if I made the default an EmptyObject and assigned it a number.
I would expect it to fail because of a type mismatch like we do for other.

~>  packer inspect /tmp
Packer Inspect: HCL2 mode

> input-variables:

var.bar: "1"
var.foo: "{\n  \"key\" = \"---\"\n}"

> local-variables:


> builds:

// test.auto.pkrvars.hcl
bar = 1

// test.pkr.hcl
variable "foo" {
  default = {
    "key" : "---"
  }
}

variable "bar" {
  default = {}
}

locals {
  baz = merge(var.foo, var.bar)
}

[azr]

Yeah, that is a super valid point. I opened zclconf/go-cty#122 to see if this could be a good idea.

[azr]

Note that for Terraform here, the default type is always ignored, so your example would just work.

[nywilken]

Note that for Terraform here, the default type is always ignored, so your example would just work.

Yeah, I def. thought about that. TBH I think users would know better what to expect here. So I'm good with merging. If users find anything confusing we can revisit. Unless you prefer to hold until you get a response from the go-cty repo.

[azr]

Hey @nywilken, yup, I think this can be merged. I need to add tests first !

The TLDR is that the conversion to a type only ensures that the receiving type has all attributes of the 'being-converted' object, so, this is intended and will always work. So for now, I think this PR ignoring these makes sense.

The next solution will be like I said in the issue to :

do like Terraform, and avoid using the default value's type as the type

(which changes behavior a little, but it's okay, because in any case, it is always better to set the type for an input var)

[azr]

Closing this one in favor of #11566 to avoid conflict

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