support for --argstr in the nix-build tf module

terraform/nix-build/main.tf

@@ -1,4 +1,7 @@
 locals {
+  nix_argstrs = jsonencode({
+    argstrs = { for k, v in var.nix_argstrs : k => v }
+  })
   nix_options = jsonencode({
     options = { for k, v in var.nix_options : k => v }
   })
@@ -8,6 +11,7 @@ data "external" "nix-build" {
   query = {
     attribute = var.attribute
     file = var.file
+    nix_argstrs = local.nix_argstrs
     nix_options = local.nix_options
     special_args = jsonencode(var.special_args)
   }

terraform/nix-build/nix-build.sh

@@ -1,8 +1,13 @@
 #!/usr/bin/env bash
 set -efu
 
-declare file attribute nix_options special_args
-eval "$(jq -r '@sh "attribute=\(.attribute) file=\(.file) nix_options=\(.nix_options) special_args=\(.special_args)"')"
+declare file attribute nix_argstrs nix_options special_args
+eval "$(jq -r '@sh "attribute=\(.attribute) file=\(.file) nix_argstrs=\(.nix_argstrs) nix_options=\(.nix_options) special_args=\(.special_args)"')"
+if [ "${nix_argstrs}" != '{"argstrs":{}}' ]; then
+  argstrs=$(echo "${nix_argstrs}" | jq -r '.argstrs | to_entries | map("--argstr \(.key) \(.value)") | join(" ")')
+else
+  argstrs=""
+fi
 if [ "${nix_options}" != '{"options":{}}' ]; then
   options=$(echo "${nix_options}" | jq -r '.options | to_entries | map("--option \(.key) \(.value)") | join(" ")')
 else
@@ -12,7 +17,7 @@ if [[ ${special_args-} == "{}" ]]; then
   # no special arguments, proceed as normal
   if [[ -n ${file-} ]] && [[ -e ${file-} ]]; then
     # shellcheck disable=SC2086
-    out=$(nix build --no-link --json $options -f "$file" "$attribute")
+    out=$(nix build --no-link --json $argstrs $options -f "$file" "$attribute")
   else
     # shellcheck disable=SC2086
     out=$(nix build --no-link --json ${options} "$attribute")

terraform/nix-build/variables.tf

@@ -9,6 +9,12 @@ variable "file" {
   default = null
 }
 
+variable "nix_argstrs" {
+  type = map(string)
+  description = "the argstrs of nix"
+  default = {}
+}
+
 variable "nix_options" {
   type = map(string)
   description = "the options of nix"