refactor: Remove unnecessary SQL.UsageError parameter from PoolAcqTimeoutObs

PoolAcqTimeoutObs is always created with SQL.AcquisitionTimeoutUsageError so the parameter does not provide any useful information.
On the other hand, it complicates debouncing logic in Logger as logWithDebounce has to lazily create the debouncer (which is error prone and hence the logic has a race condition).

This change removes the parameter from PoolAcqTimeoutObs. It is a prerequisite to simplifying logWithDebounce.

src/PostgREST/AppState.hs

@@ -222,7 +222,7 @@ usePool AppState{stateObserver=observer, stateMainThreadId=mainThreadId, ..} ses
 
   whenLeft res (\case
     SQL.AcquisitionTimeoutUsageError ->
-      observer $ PoolAcqTimeoutObs SQL.AcquisitionTimeoutUsageError
+      observer PoolAcqTimeoutObs
     err@(SQL.ConnectionUsageError e) ->
       let failureMessage = BS.unpack $ fromMaybe mempty e in
       when (("FATAL:  password authentication failed" `isInfixOf` failureMessage) || ("no password supplied" `isInfixOf` failureMessage)) $ do

src/PostgREST/Logger.hs

@@ -88,7 +88,7 @@ shouldLogResponse logLevel = case logLevel of
 -- All observations are logged except some that depend on the log-level
 observationLogger :: LoggerState -> LogLevel -> ObservationHandler
 observationLogger loggerState logLevel obs = case obs of
-  o@(PoolAcqTimeoutObs _) -> do
+  o@PoolAcqTimeoutObs -> do
     when (logLevel >= LogError) $ do
       logWithDebounce loggerState $
         logWithZTime loggerState $ observationMessage o

src/PostgREST/Metrics.hs

@@ -50,7 +50,7 @@ init configDbPoolSize = do
 -- Only some observations are used as metrics
 observationMetrics :: MetricsState -> ObservationHandler
 observationMetrics MetricsState{..} obs = case obs of
-  (PoolAcqTimeoutObs _) -> do
+  PoolAcqTimeoutObs -> do
     incCounter poolTimeouts
   (HasqlPoolObs (SQL.ConnectionObservation _ status)) -> case status of
      SQL.ReadyForUseConnectionStatus  -> do

src/PostgREST/Observation.hs

@@ -59,7 +59,7 @@ data Observation
   | QueryErrorCodeHighObs SQL.UsageError
   | QueryPgVersionError SQL.UsageError
   | PoolInit Int
-  | PoolAcqTimeoutObs SQL.UsageError
+  | PoolAcqTimeoutObs
   | HasqlPoolObs SQL.Observation
   | PoolRequest
   | PoolRequestFullfilled
@@ -140,8 +140,7 @@ observationMessage = \case
      "Config reloaded"
   PoolInit poolSize ->
      "Connection Pool initialized with a maximum size of " <> show poolSize <> " connections"
-  PoolAcqTimeoutObs usageErr ->
-    jsonMessage usageErr
+  PoolAcqTimeoutObs -> jsonMessage SQL.AcquisitionTimeoutUsageError
   HasqlPoolObs (SQL.ConnectionObservation uuid status) ->
     "Connection " <> show uuid <> (
       case status of