fix: improve error message when job has 0 machines

when a job is not yet in running state the program runs but the function
that lists the job's machines returns zero machines which can cause a
panic from division by 0 which is not a very helpful message. this
commit improves the error/warn messages when no machines are listed for
a job.

2 files changed, 11 insertions, 0 deletions

diff --git a/src/main.rs b/src/main.rs
index 6e12d6f..853c584 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1004,6 +1004,10 @@ fn machine_generate_configs(
     machines: &[Machine],
     addr_policy: &AddressAllocationPolicy,
 ) -> Result<Vec<MachineConfig>> {
+    if machines.is_empty() {
+        return Err(eyre::eyre!("cannot generate config for zero machines"));
+    }
+
     let mut configs = Vec::default();
     let mut addresses = Vec::default();
     let mut address_to_index = HashMap::<Ipv4Addr, usize>::default();
diff --git a/src/oar.rs b/src/oar.rs
index fb73109..7f0188f 100644
--- a/src/oar.rs
+++ b/src/oar.rs
@@ -138,6 +138,13 @@ fn extract_machines_from_oar_stat_json(output: &str, job_id: u32) -> Result<Vec<
             None => return Err(eyre::eyre!("unknown machine: '{hostname}'")),
         }
     }
+
+    if machines.is_empty() {
+        tracing::warn!(
+            "unable to find any machines for job id {job_id}. perhaps the job is not yet in the running state?"
+        );
+    }
+
     Ok(machines)
 }