Add ifLet SwiftUI integration warning (#3089)

* Add `ifLet` SwiftUI integration warning

We recently added a warning when we detect that `forEach` wasn't
integrated with a reducer when path elements are pushed or popped from
the stack, and I realized that we could do similarly for `ifLet` during
dismissal.

* docc

Sources/ComposableArchitecture/Documentation.docc/Articles/TreeBasedNavigation.md

@@ -115,7 +115,7 @@ struct InventoryView: View {
 ```
 
 > Note: We use SwiftUI's `@Bindable` property wrapper to produce a binding to a store, which can be
-> further scoped using ``SwiftUI/Binding/scope(state:action:)-4mj4d``.
+> further scoped using ``SwiftUI/Binding/scope(state:action:fileID:line:)``.
 
 With those few steps completed the domains and views of the parent and child features are now
 integrated together, and when the `addItem` state flips to a non-`nil` value the sheet will be
@@ -269,8 +269,8 @@ struct InventoryView: View {
 }
 ```
 
-And then in the `body` of the view you can use the ``SwiftUI/Binding/scope(state:action:)-4mj4d``
-operator to derive bindings from `$store`:
+And then in the `body` of the view you can use the
+``SwiftUI/Binding/scope(state:action:fileID:line:)`` operator to derive bindings from `$store`:
 
 ```swift
 var body: some View {

Sources/ComposableArchitecture/Documentation.docc/Extensions/Store.md

@@ -29,7 +29,7 @@
 
 ### Scoping store bindings
 
-- ``SwiftUI/Binding/scope(state:action:)-4mj4d``
+- ``SwiftUI/Binding/scope(state:action:fileID:line:)``
 - ``SwiftUI/Binding/scope(state:action:)-35r82``
 
 ### Combine integration

Sources/ComposableArchitecture/Documentation.docc/Extensions/SwiftUIIntegration.md

@@ -17,7 +17,7 @@ designed with SwiftUI in mind, and comes with many powerful tools to integrate i
 
 ### Presentation
 
-- ``SwiftUI/Binding/scope(state:action:)-4mj4d``
+- ``SwiftUI/Binding/scope(state:action:fileID:line:)``
 
 ### Navigation stacks and links
 

Sources/ComposableArchitecture/Documentation.docc/Tutorials/BuildingSyncUps/04-PresentingSyncUpForm/PresentingSyncUpForm.tutorial

@@ -112,8 +112,8 @@
 
       Luckily the library comes with the tools necessary. Just as there is a scoping operation on
       stores for focusing on sub-domains of a parent domain, there is also a scope on _bindings_ of
-      stores for doing the same: ``SwiftUI/Binding/scope(state:action:)-4mj4d``. This tool can be
-      used to derive a binding that is appropriate to pass to `sheet(item:)`.
+      stores for doing the same: ``SwiftUI/Binding/scope(state:action:fileID:line:)``. This tool can
+      be used to derive a binding that is appropriate to pass to `sheet(item:)`.
 
       @Step {
         Since we want to derive bindings from the store we need to decorate the property in the view
@@ -127,8 +127,8 @@
       }
 
       @Step {
-        Use the ``SwiftUI/Binding/scope(state:action:)-4mj4d`` operator on `$store` to focus the
-        binding to the presentation domain of the `SyncUpForm`. The `sheet(item:)` modifier will 
+        Use the ``SwiftUI/Binding/scope(state:action:fileID:line:)`` operator on `$store` to focus
+        the binding to the presentation domain of the `SyncUpForm`. The `sheet(item:)` modifier will
         hand the trailing closure a `StoreOf<SyncUpForm>`, and that is exactly what can be handed to
         the `SyncUpFormView`.
 

Sources/ComposableArchitecture/Documentation.docc/Tutorials/BuildingSyncUps/06-SyncUpDetail/EditingAndDeletingSyncUp.tutorial

@@ -70,7 +70,7 @@
 
       @Step {
         At the very bottom of the view use the `sheet(item:)` modifier by deriving a binding to the 
-        `SyncUpForm` domain using ``SwiftUI/Binding/scope(state:action:)-4mj4d``.
+        `SyncUpForm` domain using ``SwiftUI/Binding/scope(state:action:fileID:line:)``.
 
         @Code(name: "SyncUpDetail.swift", file: EditingAndDeletingSyncUp-01-code-0006.swift)
       }

Sources/ComposableArchitecture/Observation/NavigationStack+Observation.swift

@@ -70,7 +70,7 @@ import SwiftUI
   extension SwiftUI.Bindable {
     /// Derives a binding to a store focused on ``StackState`` and ``StackAction``.
     ///
-    /// See ``SwiftUI/Binding/scope(state:action:)-4mj4d`` defined on `Binding` for more
+    /// See ``SwiftUI/Binding/scope(state:action:fileID:line:)`` defined on `Binding` for more
     /// information.
     public func scope<State: ObservableState, Action, ElementState, ElementAction>(
       state: KeyPath<State, StackState<ElementState>>,
@@ -88,7 +88,7 @@ import SwiftUI
   extension Perception.Bindable {
     /// Derives a binding to a store focused on ``StackState`` and ``StackAction``.
     ///
-    /// See ``SwiftUI/Binding/scope(state:action:)-4mj4d`` defined on `Binding` for more
+    /// See ``SwiftUI/Binding/scope(state:action:fileID:line:)`` defined on `Binding` for more
     /// information.
     public func scope<State: ObservableState, Action, ElementState, ElementAction>(
       state: KeyPath<State, StackState<ElementState>>,

Sources/ComposableArchitecture/Observation/Store+Observation.swift

@@ -152,10 +152,18 @@
     /// - Returns: A binding of an optional child store.
     public func scope<State: ObservableState, Action, ChildState, ChildAction>(
       state: KeyPath<State, ChildState?>,
-      action: CaseKeyPath<Action, PresentationAction<ChildAction>>
+      action: CaseKeyPath<Action, PresentationAction<ChildAction>>,
+      fileID: StaticString = #fileID,
+      line: UInt = #line
     ) -> Binding<Store<ChildState, ChildAction>?>
     where Value == Store<State, Action> {
-      self[state: state, action: action]
+      self[
+        state: state,
+        action: action,
+        isInViewBody: _isInPerceptionTracking,
+        fileID: "\(fileID)",
+        line: line
+      ]
     }
   }
 
@@ -209,10 +217,18 @@
     /// - Returns: A binding of an optional child store.
     public func scope<State: ObservableState, Action, ChildState, ChildAction>(
       state: KeyPath<State, ChildState?>,
-      action: CaseKeyPath<Action, PresentationAction<ChildAction>>
+      action: CaseKeyPath<Action, PresentationAction<ChildAction>>,
+      fileID: StaticString = #fileID,
+      line: UInt = #line
     ) -> Binding<Store<ChildState, ChildAction>?>
     where Value == Store<State, Action> {
-      self[state: state, action: action]
+      self[
+        state: state,
+        action: action,
+        isInViewBody: _isInPerceptionTracking,
+        fileID: "\(fileID)",
+        line: line
+      ]
     }
   }
 
@@ -269,18 +285,29 @@
     /// - Returns: A binding of an optional child store.
     public func scope<State: ObservableState, Action, ChildState, ChildAction>(
       state: KeyPath<State, ChildState?>,
-      action: CaseKeyPath<Action, PresentationAction<ChildAction>>
+      action: CaseKeyPath<Action, PresentationAction<ChildAction>>,
+      fileID: StaticString = #fileID,
+      line: UInt = #line
     ) -> Binding<Store<ChildState, ChildAction>?>
     where Value == Store<State, Action> {
-      self[state: state, action: action]
+      self[
+        state: state,
+        action: action,
+        isInViewBody: _isInPerceptionTracking,
+        fileID: "\(fileID)",
+        line: line
+      ]
     }
   }
 
   extension Store where State: ObservableState {
-    fileprivate subscript<ChildState, ChildAction>(
+    @_spi(Internals)
+    public subscript<ChildState, ChildAction>(
       state state: KeyPath<State, ChildState?>,
       action action: CaseKeyPath<Action, PresentationAction<ChildAction>>,
-      isInViewBody isInViewBody: Bool = _isInPerceptionTracking
+      isInViewBody isInViewBody: Bool,
+      fileID fileID: String,
+      line line: UInt
     ) -> Store<ChildState, ChildAction>? {
       get {
         #if DEBUG && !os(visionOS)
@@ -294,6 +321,30 @@
       set {
         if newValue == nil, self.state[keyPath: state] != nil, !self._isInvalidated() {
           self.send(action(.dismiss))
+          if self.state[keyPath: state] != nil {
+            runtimeWarn(
+              """
+              SwiftUI dismissed a view through a binding at "\(fileID):\(line)", but the store \
+              destination wasn't set to "nil".
+
+              This usually means an "ifLet" has not been integrated with the reducer powering the \
+              store, and this reducer is responsible for handling presentation actions.
+
+              To fix this, ensure that "ifLet" is invoked from the reducer's "body":
+
+                  Reduce { state, action in
+                    // ...
+                  }
+                  .ifLet(\\.destination, action: \\.destination) {
+                    Destination()
+                  }
+
+              And ensure that every parent reducer is integrated into the root reducer that powers \
+              the store.
+              """
+            )
+            return
+          }
         }
       }
     }

Tests/ComposableArchitectureTests/RuntimeWarningTests.swift

@@ -273,6 +273,57 @@
             """
         }
       }
+
+      @Reducer
+      struct TestStoreDestination_NotIntegrated {
+        @Reducer
+        struct Destination {}
+        @ObservableState
+        struct State: Equatable {
+          @Presents var destination: Destination.State?
+        }
+        enum Action {
+          case destination(PresentationAction<Destination.Action>)
+        }
+      }
+      @MainActor
+      func testStoreDestination_NotIntegrated() {
+        let store = Store(
+          initialState: TestStoreDestination_NotIntegrated.State(destination: .init())
+        ) {
+          TestStoreDestination_NotIntegrated()
+        }
+
+        XCTExpectFailure {
+          store[
+            state: \.destination,
+            action: \.destination,
+            isInViewBody: false,
+            fileID: "file.swift",
+            line: 1
+          ] = nil
+        } issueMatcher: {
+          $0.compactDescription == """
+            SwiftUI dismissed a view through a binding at "file.swift:1", but the store \
+            destination wasn't set to "nil".
+
+            This usually means an "ifLet" has not been integrated with the reducer powering the \
+            store, and this reducer is responsible for handling presentation actions.
+
+            To fix this, ensure that "ifLet" is invoked from the reducer's "body":
+
+                Reduce { state, action in
+                  // ...
+                }
+                .ifLet(\\.destination, action: \\.destination) {
+                  Destination()
+                }
+
+            And ensure that every parent reducer is integrated into the root reducer that powers \
+            the store.
+            """
+        }
+      }
     #endif
   }
 #endif