Gate onMainActor routing DSL to Swift 5.10+

Author: louisdebaere

MobiusCore/Source/EffectHandlers/EffectRouterDSL.swift

@@ -40,10 +40,12 @@ public extension _PartialEffectRouter {
     /// Route main-isolated effects through the same queue path as `.on(queue: .main)`.
     ///
     /// This returns a dedicated builder exposing `to(...)` for `@MainActor` closures.
+    #if compiler(>=5.10)
     @available(iOS 13.0, macOS 10.15, tvOS 13.0, watchOS 6.0, *)
     func onMainActor() -> _MainActorPartialEffectRouter<Effect, EffectParameters, Event> {
         return _MainActorPartialEffectRouter(partialRouter: on(queue: .main))
     }
+    #endif
 
     /// Route to a closure which returns an optional event when given the parameters as input.
     ///
@@ -62,6 +64,7 @@ public extension _PartialEffectRouter {
     }
 }
 
+#if compiler(>=5.10)
 /// A `_MainActorPartialEffectRouter` represents the state between an `onMainActor` call and a `to`.
 ///
 /// Client code should not refer to this type directly.
@@ -78,14 +81,9 @@ public extension _MainActorPartialEffectRouter {
         _ fireAndForget: @MainActor @Sendable @escaping (EffectParameters) -> Void
     ) -> EffectRouter<Effect, Event> {
         return partialRouter.to { parameters, callback in
-            #if compiler(>=5.10)
-                MainActor.assumeIsolated {
-                    fireAndForget(parameters)
-                }
-            #else
-                dispatchPrecondition(condition: .onQueue(.main))
+            MainActor.assumeIsolated {
                 fireAndForget(parameters)
-            #endif
+            }
             callback.end()
             return AnonymousDisposable {}
         }
@@ -101,16 +99,12 @@ public extension _MainActorPartialEffectRouter where EffectParameters == Void {
         _ fireAndForget: @MainActor @Sendable @escaping () -> Void
     ) -> EffectRouter<Effect, Event> {
         return partialRouter.to { _, callback in
-            #if compiler(>=5.10)
-                MainActor.assumeIsolated {
-                    fireAndForget()
-                }
-            #else
-                dispatchPrecondition(condition: .onQueue(.main))
+            MainActor.assumeIsolated {
                 fireAndForget()
-            #endif
+            }
             callback.end()
             return AnonymousDisposable {}
         }
     }
 }
+#endif

MobiusCore/Test/EffectHandlers/EffectRouterDSLTests.swift

@@ -202,6 +202,7 @@ class EffectRouterDSLTests: QuickSpec {
                 expect(didDispatchEvents).to(beFalse())
             }
 
+            #if compiler(>=5.10)
             it("Supports routing to an onMainActor side-effecting function") {
                 guard #available(iOS 13.0, macOS 10.15, tvOS 13.0, watchOS 6.0, *) else {
                     return
@@ -245,6 +246,7 @@ class EffectRouterDSLTests: QuickSpec {
                 expect(effectPerformedCount.items).toEventually(equal([1]))
                 expect(didDispatchEvents).to(beFalse())
             }
+            #endif
 
             it("Supports routing to an event-returning function") {
                 var events: [Event] = []