Track how often target branches evaluate, to setup a potential alert for it.

ofborg/build.rs

@@ -248,6 +248,13 @@ fn events() -> Vec<MetricType> {
                 ("branch", "String"),
             ]),
         ),
+        Metric::ticker(
+            "TargetBranchFailsEvaluation",
+            "Number of PR evaluations which failed because the target branch failed",
+            Some(vec![
+                ("branch", "String"),
+            ]),
+        ),
         Metric::ticker(
             "JobDecodeSuccess",
             "Number of successfully decoded jobs",

ofborg/src/tasks/massrebuilder.rs

@@ -196,6 +196,7 @@ impl<E: stats::SysEvents + 'static> worker::SimpleWorker for MassRebuildWorker<E
                 file_to_str(&mut output),
             ));
 
+            self.events.notify(Event::TargetBranchFailsEvaluation(target_branch.clone()));
             overall_status.set_with_description(
                 format!("Target branch {} doesn't evaluate!", &target_branch).as_ref(),
                 hubcaps::statuses::State::Failure,