push green meta builds to the attic cache and record cached

swarm-builder/src/nix_build.rs

@@ -59,6 +59,9 @@ pub struct Builder {
     pub lock_deadline: Duration,
     /// The platform this host builds for, reported with each meta build.
     pub system: String,
+    /// Where a meta build's closure is pushed after it succeeds; `None` pushes
+    /// nothing.
+    pub cache: Option<crate::push::Remote>,
 }
 
 impl Builder {
@@ -88,6 +91,7 @@ impl Builder {
                 Reply::Built { out_path } => FromMetaReply::Built {
                     out_path,
                     system: self.system.clone(),
+                    cached: false,
                 },
                 Reply::Failed { error_tail } => FromMetaReply::Failed { error_tail },
             },
@@ -437,6 +441,7 @@ mod tests {
             deadline: BUILD_DEADLINE,
             lock_deadline: LOCK_DEADLINE,
             system: "x86_64-linux".to_owned(),
+            cache: None,
         }
     }
 
@@ -514,6 +519,7 @@ mod tests {
             FromMetaReply::Built {
                 out_path: format!("{} {}", BUILD_FLAGS.join(" "), b.meta_attr(&meta_job())),
                 system: "x86_64-linux".to_owned(),
+                cached: false,
             }
         );
     }