Update to thread warnings.

Sources/ComposableArchitecture/Store.swift

@@ -120,6 +120,9 @@ public final class Store<State, Action> {
   private var parentCancellable: AnyCancellable?
   private let reducer: (inout State, Action) -> Effect<Action, Never>
   private var bufferedActions: [Action] = []
+  #if DEBUG
+  private var initialThread = Thread.current
+  #endif
 
   /// Initializes a store from an initial state, a reducer, and an environment.
   ///
@@ -322,7 +325,6 @@ public final class Store<State, Action> {
     action fromLocalAction: @escaping (LocalAction) -> Action
   ) -> AnyPublisher<Store<LocalState, LocalAction>, Never>
   where P.Output == LocalState, P.Failure == Never {
-
     func extractLocalState(_ state: State) -> LocalState? {
       var localState: LocalState?
       _ = toLocalState(Just(state).eraseToAnyPublisher())
@@ -365,7 +367,9 @@ public final class Store<State, Action> {
     self.publisherScope(state: toLocalState, action: { $0 })
   }
 
-  func send(_ action: Action) {
+  func send(_ action: Action, isFromViewStore: Bool = true) {
+    self.threadCheck(status: .send(action, isFromViewStore: isFromViewStore))
+
     self.bufferedActions.append(action)
     guard !self.isSending else { return }
 
@@ -382,45 +386,14 @@ public final class Store<State, Action> {
 
       var didComplete = false
       let uuid = UUID()
-
-      #if DEBUG
-        let initalThread = Thread.current
-        initalThread.threadDictionary[uuid] = true
-      #endif
-
       let effectCancellable = effect.sink(
         receiveCompletion: { [weak self] _ in
-          #if DEBUG
-            if Thread.current.threadDictionary[uuid] == nil {
-              breakpoint(
-                """
-                ---
-                Warning: Store.send
-
-                The Store class is not thread-safe, and so all interactions with an instance of Store
-                (including all of its scopes and derived ViewStores) must be done on the same thread.
-
-                \(debugCaseOutput(action)) has produced an Effect that was completed on a different thread \
-                from the one it was executed on.
-
-                Starting thread: \(initalThread)
-                Final thread: \(Thread.current)
-
-                Possible fixes for this are:
-
-                * Add a .receive(on:) to the Effect to ensure it completes on this Stores correct thread.
-                """
-              )
-            }
-
-            Thread.current.threadDictionary[uuid] = nil
-          #endif
-
+          self?.threadCheck(status: .effectCompletion(action))
           didComplete = true
           self?.effectCancellables[uuid] = nil
         },
         receiveValue: { [weak self] action in
-          self?.send(action)
+          self?.send(action, isFromViewStore: false)
         }
       )
 
@@ -440,4 +413,59 @@ public final class Store<State, Action> {
     func absurd<A>(_ never: Never) -> A {}
     return self.scope(state: { $0 }, action: absurd)
   }
+
+  private enum ThreadCheckStatus {
+    case effectCompletion(Action)
+    case send(Action, isFromViewStore: Bool)
+  }
+
+  @inline(__always)
+  private func threadCheck(status: ThreadCheckStatus) {
+    #if DEBUG
+    guard self.initialThread != Thread.current
+    else { return }
+
+    let message: String
+    switch status {
+    case let .effectCompletion(action):
+      message = """
+        An effect returned from the action "\(debugCaseOutput(action))" completed on the \
+        wrong thread. Make sure to use ".receive(on:)" on any effects that execute on background \
+        threads to receive their output on the initial thread.
+        """
+
+    case let .send(action, isFromViewStore: true):
+      message = """
+        "ViewStore.send(\(debugCaseOutput(action)))" was called on the wrong thread. Make \
+        sure that "ViewStore.send" is always called on the initial thread.
+        """
+
+    case let .send(action, isFromViewStore: false):
+      message = """
+        An effect emitted the action "\(debugCaseOutput(action))" from the wrong thread. Make sure \
+        to use ".receive(on:)" on any effects that execute on background threads to receive their \
+        output on the initial thread.
+        """
+    }
+
+    breakpoint(
+      """
+      ---
+      Warning:
+
+      The store was interacted with on a thread that is different from the thread the store was \
+      created on:
+
+      \(message)
+
+        Initial thread: \(self.initialThread)
+        Current thread: \(Thread.current)
+
+      The "Store" class is not thread-safe, and so all interactions with an instance of "Store" \
+      (including all of its scopes and derived view stores) must be done on the same thread.
+      ---
+      """
+    )
+    #endif
+  }
 }

Sources/ComposableArchitecture/ViewStore.swift

@@ -71,7 +71,7 @@ public final class ViewStore<State, Action>: ObservableObject {
     _ store: Store<State, Action>,
     removeDuplicates isDuplicate: @escaping (State, State) -> Bool
   ) {
-    self._send = store.send
+    self._send = { store.send($0) }
     self._state = CurrentValueSubject(store.state.value)
 
     self.viewCancellable = store.state

Tests/ComposableArchitectureTests/DebugTests.swift

@@ -112,14 +112,18 @@ final class DebugTests: XCTestCase {
   }
 
   func testBindingAction() {
+    struct State {
+      @BindableState var width = 0
+    }
+
     var dump = ""
-    customDump(BindingAction.set(\CGSize.width, 50), to: &dump)
+    customDump(BindingAction.set(\State.$width, 50), to: &dump)
     XCTAssertNoDifference(
       dump,
       #"""
       BindingAction.set(
-        \CGSize.width,
-        50.0
+        WritableKeyPath<State, BindableState<Int>>,
+        50
       )
       """#
     )