lang: Fix crash in lookup function

[radeksimko]

Previously a config like this:

locals {
  terraform_versions = {
    "terraform-provider-aws" = "0.10+"
  }
}
provider "github" {
  organization = var.organization_name
  token = var.github_token
}

data "github_repositories" "providers" {
  query = "org:${var.organization_name} archived:false aws OR azurerm OR google OR opc OR vsphere OR kubernetes"
}

data "github_repository" "provider" {
  count = length(data.github_repositories.providers.full_names)
  full_name = sort(data.github_repositories.providers.full_names)[count.index]
}

data "template_file" "readme" {
  count = length(data.github_repository.provider.*.ssh_clone_url)

  template = file("./templates/README.md")

  vars = {
    go_version = lookup(local.go_versions, data.github_repository.provider.*.name[count.index], local.default_go_version)
  }
}

caused a crash:

https://gist.github.com/radeksimko/012c83a42c9f6b647912b62b77e4f8ed

[apparentlymart]

Doing this check in here does seem right but I don't think returning the "default" value type here is the right fallback for a couple reasons:

• There might not be a default value (it's optional, and so I think this might cause an out-of-bounds panic)
• Once we do know the key (at apply time) we might find that it matches one of the attributes in inputMap after all, and so that'll be the type of our result.

With both of those things in mind, I think the best we can do in this scenario is return cty.DynamicPseudoType, nil, which effectively means "I don't know yet what the result type will be". That's an okay response when arguments are unknown: it'll just mean we won't catch a type error here during the plan operation. We'll re-run the function again at apply time when we've learned more information, and thus catch any name error there, as usual for unknown values.

[radeksimko]

That makes sense. I made that change - PTAL.

[apparentlymart]

LGTM, thanks!

[ghost]

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