Allow silencing RLA by setting the label rla-silence

If a test is not run by Bors and the label `rla-silence` is applied to a
PR, do not post an update messsage. This will allow keeping RLA message
noise out of PRs that are expected to have a lot of churn.

Fixes #73

src/bin/server/worker.rs

@@ -10,6 +10,7 @@ use std::str;
 use std::time::{Duration, Instant};
 
 const MINIMUM_DELAY_BETWEEN_INDEX_BACKUPS: Duration = Duration::from_secs(60 * 60);
+const SILENCE_LABEL: &str = "rla-silenced";
 
 pub struct Worker {
     debug_post: Option<(String, u32)>,
@@ -270,6 +271,14 @@ impl Worker {
                 info!("Build results outdated, skipping report.");
                 return Ok(());
             }
+            if pr_info
+                .labels
+                .iter()
+                .any(|label| label.name == SILENCE_LABEL)
+            {
+                info!("PR has label `{SILENCE_LABEL}`, skipping report");
+                return Ok(());
+            }
         }
 
         let (repo, pr) = match self.debug_post {

src/github.rs

@@ -61,13 +61,19 @@ pub struct CommitStatusEvent {
 #[derive(Deserialize)]
 pub struct Pr {
     pub head: PrCommitRef,
+    pub labels: Vec<Label>,
 }
 
 #[derive(Deserialize)]
 pub struct PrCommitRef {
     pub sha: String,
 }
 
+#[derive(Deserialize)]
+pub struct Label {
+    pub name: String,
+}
+
 #[derive(Deserialize)]
 pub struct CommitMeta {
     pub commit: Commit,