feat: Add delete-old flag to automatically remove old generations

Signed-off-by: James Alseth <james@jalseth.me>

src/command/apply.rs

@@ -71,6 +71,12 @@ To upload keys without building or deploying the rest of the configuration, use
         long_help = "Reboots nodes after activation and waits for them to come back up."
     )]
     reboot: bool,
+    #[arg(
+        long,
+        help = "Delete old NixOS generations.",
+        long_help = "Automatically delete previous NixOS generation after a succesful deployment. If the reboot flag is enabled, this is performed after the reboot."
+    )]
+    delete_old: bool,
     #[arg(
         long,
         alias = "no-substitutes",
@@ -153,6 +159,7 @@ pub async fn run(hive: Hive, opts: Opts) -> Result<(), ColmenaError> {
                 verbose,
                 no_keys,
                 reboot,
+                delete_old,
                 no_substitute,
                 no_gzip,
                 build_on_target,
@@ -195,6 +202,7 @@ pub async fn run(hive: Hive, opts: Opts) -> Result<(), ColmenaError> {
         options.set_gzip(!no_gzip);
         options.set_upload_keys(!no_keys);
         options.set_reboot(reboot);
+        options.set_delete_old(delete_old);
         options.set_force_replace_unknown_profiles(force_replace_unknown_profiles);
         options.set_evaluator(evaluator);
 

src/job.rs

@@ -101,6 +101,9 @@ pub enum JobType {
 
     /// Rebooting a host.
     Reboot,
+
+    /// Delete old NixOS generations.
+    DeleteOld,
 }
 
 /// A handle to a job.

src/nix/deployment/mod.rs

@@ -671,6 +671,26 @@ impl Deployment {
             target
         };
 
+        // Delete old generations
+        let mut target = if self.options.delete_old {
+            let job = parent.create_job(JobType::DeleteOld, nodes.clone())?;
+            job.run_waiting(|job| async move {
+                job.state(JobState::Running)?;
+                job.message("Deleting old NixOS generations...".to_string())?;
+
+                let host = target.host.as_mut().unwrap();
+                host.set_job(Some(job.clone()));
+                host.run_command(&["nix-collect-garbage", "--delete-old"])
+                    .await?;
+
+                job.success_with_message("Deleted old NixOS generations.".to_string())?;
+                Ok(target)
+            })
+            .await?
+        } else {
+            target
+        };
+
         // Upload post-activation keys
         if self.options.upload_keys {
             let job = parent.create_job(JobType::UploadKeys, nodes.clone())?;

src/nix/deployment/options.rs

@@ -19,6 +19,9 @@ pub struct Options {
     /// Whether to reboot the hosts after activation.
     pub(super) reboot: bool,
 
+    /// Whether to automatically delete previous NixOS generations.
+    pub(super) delete_old: bool,
+
     /// Whether to create GC roots for node profiles.
     ///
     /// If true, .gc_roots will be created under the hive's context
@@ -69,6 +72,10 @@ impl Options {
         self.reboot = enable;
     }
 
+    pub fn set_delete_old(&mut self, enable: bool) {
+        self.delete_old = enable;
+    }
+
     pub fn set_create_gc_roots(&mut self, enable: bool) {
         self.create_gc_roots = enable;
     }
@@ -101,6 +108,7 @@ impl Default for Options {
             gzip: true,
             upload_keys: true,
             reboot: false,
+            delete_old: false,
             create_gc_roots: false,
             force_build_on_target: None,
             force_replace_unknown_profiles: false,