Add --keep-result to create GC roots for profiles

This resembles the behavior of morph.

Reference: #18

src/command/apply.rs

@@ -57,6 +57,15 @@ Set to 0 to disable parallemism limit.
                     Err(_) => Err(String::from("The value must be a valid number")),
                 }
             }))
+        .arg(Arg::with_name("keep-result")
+            .long("keep-result")
+            .help("Create GC roots for built profiles")
+            .long_help(r#"Create GC roots for built profiles.
+
+The built system profiles will be added as GC roots so that they will not be removed by the garbage collector.
+The links will be created under .gcroots in the directory the Hive configuration is located.
+"#)
+            .takes_value(false))
         .arg(Arg::with_name("verbose")
             .short("v")
             .long("verbose")
@@ -101,6 +110,7 @@ pub fn subcommand() -> App<'static, 'static> {
 
 pub async fn run(_global_args: &ArgMatches<'_>, local_args: &ArgMatches<'_>) {
     let hive = util::hive_from_args(local_args).unwrap();
+    let hive_base = hive.as_path().parent().unwrap().to_owned();
 
     log::info!("Enumerating nodes...");
     let all_nodes = hive.deployment_info().await.unwrap();
@@ -176,6 +186,11 @@ pub async fn run(_global_args: &ArgMatches<'_>, local_args: &ArgMatches<'_>) {
     options.set_gzip(!local_args.is_present("no-gzip"));
     options.set_progress_bar(!local_args.is_present("verbose"));
     options.set_upload_keys(!local_args.is_present("no-keys"));
+
+    if local_args.is_present("keep-result") {
+        options.set_gc_roots(hive_base.join(".gcroots"));
+    }
+
     deployment.set_options(options);
 
     if local_args.is_present("no-keys") && goal_arg == "keys" {

src/nix/deployment.rs

@@ -1,6 +1,8 @@
 use std::cmp::max;
-use std::sync::Arc;
 use std::collections::HashMap;
+use std::convert::AsRef;
+use std::path::{Path, PathBuf};
+use std::sync::Arc;
 
 use futures::future::join_all;
 use tokio::sync::{Mutex, Semaphore};
@@ -367,8 +369,7 @@ impl Deployment {
                             );
 
                             let goal = arc_self.goal;
-                            let arc_self = arc_self.clone();
-                            let profiles = arc_self.build_profiles(&chunk, drv, bar.clone()).await;
+                            let profiles = arc_self.clone().build_profiles(&chunk, drv, bar.clone()).await;
 
                             let profiles = match profiles {
                                 Some(profiles) => profiles,
@@ -385,6 +386,14 @@ impl Deployment {
                                 }
                             }
 
+                            if let Some(base) = &arc_self.options.gc_roots {
+                                // Create GC roots
+                                if let Err(e) = profiles.create_gc_roots(base).await {
+                                    let bar = progress.create_task_progress(BATCH_OPERATION_LABEL.to_string());
+                                    bar.failure(&format!("Failed to create GC roots: {:?}", e));
+                                }
+                            }
+
                             drop(permit);
                             profiles
                         };
@@ -582,7 +591,7 @@ impl ParallelismLimit {
     }
 }
 
-#[derive(Copy, Clone, Debug)]
+#[derive(Clone, Debug)]
 pub struct DeploymentOptions {
     /// Whether to show condensed progress bars.
     ///
@@ -597,6 +606,9 @@ pub struct DeploymentOptions {
 
     /// Whether to upload keys when deploying.
     upload_keys: bool,
+
+    /// Directory to create GC roots for node profiles in.
+    gc_roots: Option<PathBuf>,
 }
 
 impl Default for DeploymentOptions {
@@ -606,6 +618,7 @@ impl Default for DeploymentOptions {
             substituters_push: true,
             gzip: true,
             upload_keys: true,
+            gc_roots: None,
         }
     }
 }
@@ -627,6 +640,10 @@ impl DeploymentOptions {
         self.upload_keys = enable;
     }
 
+    pub fn set_gc_roots<P: AsRef<Path>>(&mut self, path: P) {
+        self.gc_roots = Some(path.as_ref().to_owned());
+    }
+
     fn to_copy_options(&self) -> CopyOptions {
         let options = CopyOptions::default();
 

src/nix/profile.rs

@@ -1,8 +1,11 @@
 use std::collections::HashMap;
 use std::convert::TryFrom;
-use std::ops::{Deref, DerefMut};
 use std::fs;
+use std::ops::{Deref, DerefMut};
 use std::path::Path;
+use std::process::Stdio;
+
+use tokio::process::Command;
 
 use super::{
     Goal,
@@ -110,3 +113,28 @@ impl TryFrom<Vec<StorePath>> for ProfileMap {
         }
     }
 }
+
+impl ProfileMap {
+    /// Create GC roots for all profiles in the map.
+    ///
+    /// The created links will be located at `{base}/node-{node_name}`.
+    pub async fn create_gc_roots(&self, base: &Path) -> NixResult<()> {
+        // This will actually try to build all profiles, but since they
+        // already exist only the GC roots will be created.
+        for (node, profile) in self.0.iter() {
+            let path = base.join(format!("node-{}", node));
+
+            let mut command = Command::new("nix-store");
+            command.args(&["--no-build-output", "--indirect", "--add-root", path.to_str().unwrap()]);
+            command.args(&["--realise", profile.as_path().to_str().unwrap()]);
+            command.stdout(Stdio::null());
+
+            let status = command.status().await?;
+            if !status.success() {
+                return Err(NixError::NixFailure { exit_code: status.code().unwrap() });
+            }
+        }
+
+        Ok(())
+    }
+}