Add useful panic messages if queries fail to start

compiler/rustc_query_system/src/query/plumbing.rs

@@ -44,6 +44,18 @@ enum QueryResult {
  Poisoned,
 }
 
+impl QueryResult {
+ /// Unwraps the query job expecting that it has started.
+ fn expect_job(self) -> QueryJob {
+ match self {
+ Self::Started(job) => job,
+ Self::Poisoned => {
+ panic!("job for query failed to start and was poisoned")
+ }
+ }
+ }
+}
+
 impl<K> QueryState<K>
 where
  K: Eq + Hash + Copy + Debug,
@@ -169,10 +181,7 @@ where
 
  let job = {
  let mut lock = state.active.lock_shard_by_value(&key);
- match lock.remove(&key).unwrap() {
- QueryResult::Started(job) => job,
- QueryResult::Poisoned => panic!(),
- }
+ lock.remove(&key).unwrap().expect_job()
  };
 
  job.signal_complete();
@@ -190,10 +199,8 @@ where
  let state = self.state;
  let job = {
  let mut shard = state.active.lock_shard_by_value(&self.key);
- let job = match shard.remove(&self.key).unwrap() {
- QueryResult::Started(job) => job,
- QueryResult::Poisoned => panic!(),
- };
+ let job = shard.remove(&self.key).unwrap().expect_job();
+
  shard.insert(self.key, QueryResult::Poisoned);
  job
  };
@@ -277,11 +284,14 @@ where
  // We didn't find the query result in the query cache. Check if it was
  // poisoned due to a panic instead.
  let lock = query.query_state(qcx).active.get_shard_by_value(&key).lock();
+
  match lock.get(&key) {
- // The query we waited on panicked. Continue unwinding here.
- Some(QueryResult::Poisoned) => FatalError.raise(),
+ Some(QueryResult::Poisoned) => {
+ panic!("query '{}' not cached due to poisoning", query.name())
+ }
  _ => panic!(
- "query result must in the cache or the query must be poisoned after a wait"
+ "query '{}' result must be in the cache or the query must be poisoned after a wait",
+ query.name()
  ),
  }
  })