feat: parse installables

Signed-off-by: Christina Sørensen <christina@cafkafk.com>

crates/nix-weather/src/cli.rs

@@ -6,12 +6,15 @@
 use clap::{arg, command, crate_authors, value_parser, ArgAction, Command};
 
 const DEFAULT_CACHE: &str = "cache.nixos.org";
+const DEFAULT_INSTALLABLE: &str = "./#nixosConfigurations.{}.config.system.build.toplevel";
 
 pub fn build_cli() -> Command {
   command!()
     .author(crate_authors!("\n"))
+    // TODO: parse multiple installables, like e.g. build does?
+    .arg(arg!([installable] "A nix installable").required(false))
     .arg(
-      arg!(--cache <CACHE> "check a specific cache")
+      arg!(--cache <CACHE> "Check a specific cache")
         .required(false)
         .default_value(DEFAULT_CACHE),
     )

crates/nix-weather/src/main.rs

@@ -103,7 +103,11 @@ async fn main() -> io::Result<()> {
     .build()
     .unwrap();
 
-  let binding = get_requisites(&host_name, &config_dir);
+  let binding = get_requisites(
+    &host_name,
+    &config_dir,
+    matches.get_one::<String>("installable").cloned(),
+  );
 
   let get_requisites_duration = initial_time.elapsed().as_secs();
 

crates/nix-weather/src/nix.rs

@@ -9,8 +9,9 @@ use std::{
   process::{Command, Stdio},
 };
 
-pub fn get_requisites(host: &str, config_dir: &str) -> String {
-  let get_drv_path = Command::new("nix")
+/// Get nixosConfiguration derivation path
+fn get_config_drv_path(host: &str, config_dir: &str) -> std::io::Result<std::process::Output> {
+  Command::new("nix")
     .current_dir(Path::new(config_dir))
     .args([
       "build",
@@ -23,10 +24,30 @@ pub fn get_requisites(host: &str, config_dir: &str) -> String {
       "--json",
     ])
     .output()
-    .unwrap();
+}
+
+/// Get installable derivation path
+fn get_installable_drv_path(
+  host: &str,
+  config_dir: &str,
+  installable: &str,
+) -> std::io::Result<std::process::Output> {
+  Command::new("nix")
+    .current_dir(Path::new(config_dir))
+    .args(["build", "--quiet", installable, "--dry-run", "--json"])
+    .output()
+}
+
+pub fn get_requisites(host: &str, config_dir: &str, installable: Option<String>) -> String {
+  let mut drv_path;
+  if let Some(installable) = installable {
+    drv_path = get_installable_drv_path(host, config_dir, &installable).unwrap();
+  } else {
+    drv_path = get_config_drv_path(host, config_dir).unwrap();
+  }
 
   let drv_path_json: Value =
-    serde_json::from_str(&String::from_utf8(get_drv_path.stdout).unwrap()).unwrap();
+    serde_json::from_str(&String::from_utf8(drv_path.stdout).unwrap()).unwrap();
   let drv_path = drv_path_json[0]["drvPath"].clone();
 
   log::debug!("drv_path: {}", &drv_path);