Combine and concurrency: lol

Author: groue

GRDB/Core/DatabaseRegionObservation.swift

@@ -201,7 +201,11 @@ extension DatabasePublishers {
             self.observation = observation
         }
 
-        public func receive<S>(subscriber: S) where S: Subscriber, Failure == S.Failure, Output == S.Input {
+        public func receive<S>(subscriber: S)
+        where S: Subscriber & GRDBSendableMetatype,
+              Failure == S.Failure,
+              Output == S.Input
+        {
             let subscription = DatabaseRegionSubscription(
                 writer: writer,
                 observation: observation,
@@ -212,7 +216,7 @@ extension DatabasePublishers {
 
     private class DatabaseRegionSubscription<Downstream>:
         Subscription, @unchecked Sendable
-    where Downstream: Subscriber,
+    where Downstream: Subscriber & GRDBSendableMetatype,
           Downstream.Failure == Error,
           Downstream.Input == Database
     {

GRDB/Utils/OnDemandFuture.swift

@@ -27,15 +27,17 @@ struct OnDemandFuture<Output, Failure: Error>: Publisher {
         self.attemptToFulfill = attemptToFulfill
     }
 
-    func receive<S>(subscriber: S) where S: Subscriber, Failure == S.Failure, Output == S.Input {
+    func receive<S>(subscriber: S) where S: Subscriber & GRDBSendableMetatype, Failure == S.Failure, Output == S.Input {
         let subscription = OnDemandFutureSubscription(
             attemptToFulfill: attemptToFulfill,
             downstream: subscriber)
         subscriber.receive(subscription: subscription)
     }
 }
 
-private class OnDemandFutureSubscription<Downstream: Subscriber>: Subscription, @unchecked Sendable {
+private class OnDemandFutureSubscription<Downstream>: Subscription, @unchecked Sendable
+where Downstream: Subscriber & GRDBSendableMetatype
+{
     // @unchecked because `state` is protected with `lock`.
     typealias Promise = @Sendable (Result<Downstream.Input, Downstream.Failure>) -> Void
 

GRDB/ValueObservation/ValueObservation.swift

@@ -511,7 +511,11 @@ extension DatabasePublishers {
             self.start = start
         }
 
-        public func receive<S>(subscriber: S) where S: Subscriber, Failure == S.Failure, Output == S.Input {
+        public func receive<S>(subscriber: S)
+        where S: Subscriber & GRDBSendableMetatype,
+              Failure == S.Failure,
+              Output == S.Input
+        {
             let subscription = ValueSubscription(
                 start: start,
                 downstream: subscriber)
@@ -521,7 +525,7 @@ extension DatabasePublishers {
 
     private class ValueSubscription<Downstream>:
         Subscription, @unchecked Sendable
-    where Downstream: Subscriber,
+    where Downstream: Subscriber & GRDBSendableMetatype,
           Downstream.Failure == Error
     {
         // @unchecked Sendable because `cancellable` and `state` are