download an agent's cached closure in prebuild, building locally when that fails

hive-c0re/src/lifecycle/mod.rs

@@ -751,6 +751,29 @@ async fn wait_bounded(
     Ok(None)
 }
 
+/// Log and record a prebuild's stdout; the last non-empty line is the
+/// toplevel `nix build --print-out-paths` printed.
+async fn pump_prebuild_stdout(
+    stdout: tokio::process::ChildStdout,
+    cmdline: String,
+    logs: Option<std::sync::Arc<crate::build_logs::BuildLogs>>,
+    log_id: Option<i64>,
+) -> Option<String> {
+    use tokio::io::{AsyncBufReadExt, BufReader};
+    let mut lines = BufReader::new(stdout).lines();
+    let mut out_path = None;
+    while let Ok(Some(line)) = lines.next_line().await {
+        tracing::info!(target: "nix-prebuild", cmdline = %cmdline, "{line}");
+        if !line.trim().is_empty() {
+            out_path = Some(line.trim().to_owned());
+        }
+        if let (Some(h), Some(id)) = (&logs, log_id) {
+            h.append_stdout(id, &line);
+        }
+    }
+    out_path
+}
+
 /// Pre-build `system.build.toplevel` against `meta#<name>` so the
 /// subsequent `nixos-container update` finds the result cached and
 /// skips straight to the profile-swap. Store-warming only — container
@@ -761,7 +784,13 @@ async fn wait_bounded(
 /// `node_id` is the queue node this build belongs to, when there is one —
 /// it is stored on the `build_logs` row so the dashboard can find the log
 /// from the node. Pass `None` for builds that run outside the queue.
-pub async fn prebuild_toplevel(name: &str, flake_ref: &str, node_id: Option<u64>) -> Result<()> {
+///
+/// Returns the toplevel `nix build` printed, `None` if it printed nothing.
+pub async fn prebuild_toplevel(
+    name: &str,
+    flake_ref: &str,
+    node_id: Option<u64>,
+) -> Result<Option<String>> {
     use tokio::io::{AsyncBufReadExt, BufReader};
     // Split `<root>#<name>` so we can re-emit with the explicit
     // `nixosConfigurations.<name>` segment. The flake_ref shape is
@@ -814,17 +843,12 @@ pub async fn prebuild_toplevel(name: &str, flake_ref: &str, node_id: Option<u64>
     let stdout = child.stdout.take().expect("piped stdout");
     let stderr = child.stderr.take().expect("piped stderr");
 
-    let stdout_cmdline = cmdline.clone();
-    let stdout_logs = logs.clone();
-    let pump_stdout = tokio::spawn(async move {
-        let mut lines = BufReader::new(stdout).lines();
-        while let Ok(Some(line)) = lines.next_line().await {
-            tracing::info!(target: "nix-prebuild", cmdline = %stdout_cmdline, "{line}");
-            if let (Some(h), Some(id)) = (&stdout_logs, log_id) {
-                h.append_stdout(id, &line);
-            }
-        }
-    });
+    let pump_stdout = tokio::spawn(pump_prebuild_stdout(
+        stdout,
+        cmdline.clone(),
+        logs.clone(),
+        log_id,
+    ));
 
     let stderr_cmdline = cmdline.clone();
     let stderr_logs = logs.clone();
@@ -860,7 +884,7 @@ pub async fn prebuild_toplevel(name: &str, flake_ref: &str, node_id: Option<u64>
             None => bail!("prebuild {cmdline} timed out after {secs}s; killed it"),
         }
     };
-    let _ = pump_stdout.await;
+    let out_path = pump_stdout.await.ok().flatten();
     let _ = pump_stderr.await;
 
     let ok = status.success();
@@ -880,7 +904,7 @@ pub async fn prebuild_toplevel(name: &str, flake_ref: &str, node_id: Option<u64>
             None => bail!("prebuild {cmdline} failed ({status})"),
         }
     }
-    Ok(())
+    Ok(out_path)
 }
 
 pub async fn list() -> Result<Vec<String>> {