feat: use persistent flake dirs to speed things up

src/image_builder.rs

@@ -210,11 +210,13 @@ impl BaseImageBuilder {
         nixos::load_store_db("/nix/.reginfo")?;
 
         // build base flake
+        let flake_dir = Path::new(crate::CACHE_HOME).join("base-flake");
         let store_path = match &self.flake_dir {
             None => nixos::build_flake_from_package_list(
                 "debug-shell",
                 "A debug shell",
                 crate::BASE_PACKAGES,
+                &flake_dir,
             )?,
             Some(flake_dir) => nixos::build_flake(flake_dir)?,
         };
@@ -226,9 +228,7 @@ impl BaseImageBuilder {
 
     fn do_package(&self) -> Result<()> {
         if self.package_output.is_none() {
-            // no packaging, run garbage collection instead
-            log::info!("running nix garbage collector");
-            return nixos::run_gc();
+            return Ok(());
         }
 
         let output = self.package_output.as_ref().unwrap();

src/nixos.rs

@@ -7,7 +7,6 @@ use std::{
 
 use anyhow::{bail, Context, Result};
 use regex::Regex;
-use tempfile::tempdir;
 
 pub(crate) const ENV_VARS: [(&str, &str); 4] = [
     ("PATH", "/nix/.bin"),
@@ -64,13 +63,11 @@ pub fn build_flake_from_package_list(
     name: &str,
     description: &str,
     packages: &[&str],
+    flake_dir: &Path,
 ) -> Result<PathBuf> {
     let mut packages: Vec<&str> = Vec::from(packages);
     packages.sort();
 
-    let flake_tmp = tempdir()?;
-    let flake_dir = flake_tmp.path();
-
     let flake_template = include_str!("templates/flake.nix");
     let re = Regex::new(r"\{\{\s*(\w+)\s*\}\}").unwrap();
 
@@ -85,6 +82,7 @@ pub fn build_flake_from_package_list(
     });
 
     log::debug!("writing flake.nix to {}", flake_dir.display());
+    fs::create_dir_all(flake_dir)?;
     fs::write(flake_dir.join("flake.nix"), flake.as_ref())?;
 
     log::debug!("building flake in {}", flake_dir.display());

src/nixpkgs.rs

@@ -285,10 +285,12 @@ pub fn remove_package(name: &str) -> Result<()> {
 
 fn build_user_env_flake(pkgs: &Packages) -> Result<()> {
     let flake_pkgs: Vec<&str> = pkgs.iter().map(|p| p.name.as_ref()).collect();
+    let flake_dir = Path::new(crate::CACHE_HOME).join("env-flake");
     let path = crate::nixos::build_flake_from_package_list(
         "user-env",
         "Dive installed packages",
         &flake_pkgs,
+        &flake_dir,
     )
     .context("failed to build flake")?;
     nixos::symlink_store_path(path, "user-env", crate::USER_ENV_DIR)?;