add attribute default

[tbugfinder]

Hi @apparentlymart,

thanks for your effort on this project.
I tried to output a variable default, however this failed.
Do you think this could be added?

$ cat test.tpl
%{ for v in variables ~}
name: ${v.name}, defaultValue:  ${v.default}, description: ${v.description})
%{ endfor ~}


terraform-config-inspect . --json | hcltemplate test.tpl

Error: Unsupported attribute

  on test.tpl line 2:
   2: ${v.name}, defaultValue:  ${v.default}, description: ${v.description}

This object does not have an attribute named "default".

Thanks & Best
TB

[tbugfinder]

This might require setting an empty string if default isn't set for a variable.

[apparentlymart]

Hi @tbugfinder,

It looks like default in terraform-config-inspect is omitted entirely when not set in the configuration, rather than explicitly set to null. I suppose that makes sense for terraform-config-inspect, but it does create a problem for templating with hcltemplate indeed.

In order to address this I think I would add a new function like Terraform's lookup to allow setting a default for an attribute that doesn't exist:

name: ${v.name}, defaultValue:  ${jsonencode(lookup(v, "default", null))}, description: ${v.description})

(I also added jsonencode here because not all values that can be set as default in Terraform can be directly converted to a string, which would create another situation where the template would fail to render.)

Unfortunately Terraform's lookup lives in Terraform itself rather than in the upstream library cty that is providing all of hcltemplate's functions here. The least involved way to get this done would be to copy that implementation from Terraform into hcltemplate, but I feel inclined to add that function to cty's "standard library" because there's nothing particularly Terraform-specific about it.

[tbugfinder]

Hi @apparentlymart,
thanks for the quick answer, including thoughts to address the issue.
Wouldn't terraform-config-inspect provide proper json output of the default value (if available)?
Do you have an estimate wether such a request would be added to cty within "weeks" :-D ?

[tbugfinder]

${jsonencode(lookup(v, "default", null))}would support different values instead of null.

[apparentlymart]

Hi @tbugfinder,

Unfortunately I will not have time to work on that change myself in the near future, because my focus is currently elsewhere. cty is another project of mine though, and I'd be happy to review a PR in that repository if someone else has the time and motivation to work on it.