Disfavor new subscript (#2875)

* Disfavor case key path for binding actions.

* wip

* fix

---------

Co-authored-by: Stephen Celis <[email protected]>

Author: mbrandonw

Sources/ComposableArchitecture/Observation/Binding+Observation.swift

@@ -224,6 +224,7 @@
   }
 
   extension Case where Value: BindableAction, Value.State: ObservableState {
+    @_disfavoredOverload
     public subscript<Member: Equatable & Sendable>(
       dynamicMember keyPath: WritableKeyPath<Value.State, Member>
     ) -> Case<Member> {

Sources/ComposableArchitecture/SwiftUI/Binding.swift

@@ -184,7 +184,7 @@ public struct BindingAction<Root>: CasePathable, Equatable, @unchecked Sendable
       ) -> AnyCasePath<BindingAction, Value> where Root: ObservableState {
         AnyCasePath(
           embed: { .set(keyPath, $0) },
-          extract: { $0.keyPath == keyPath ? $0.value as? Value : nil }
+          extract: { $0.keyPath == keyPath ? $0.value.base as? Value : nil }
         )
       }
     #endif

Tests/ComposableArchitectureTests/TestStoreTests.swift

@@ -597,6 +597,17 @@
       }
       await store.receive(\.delegate.success, 42)
     }
+
+    func testBindingTestStore_WhenStateAndActionHaveSameName() async {
+      let store = TestStore(initialState: .init()) {
+        SameNameForStateAndAction()
+      }
+      await store.send(.onAppear)
+      await store.receive(\.isOn)
+      await store.receive(\.binding.isOn) {
+        $0.isOn = true
+      }
+    }
   }
 
   private struct Client: DependencyKey {
@@ -625,4 +636,28 @@
       case delete(IndexSet)
     }
   }
+
+  @Reducer
+  struct SameNameForStateAndAction {
+    @ObservableState
+    struct State: Equatable { var isOn = false }
+    enum Action: BindableAction {
+      case binding(BindingAction<State>)
+      case onAppear
+      case isOn(Bool)
+    }
+    var body: some ReducerOf<Self> {
+      BindingReducer()
+      Reduce { state, action in
+        switch action {
+        case .binding:
+          return .none
+        case .onAppear:
+          return .send(.isOn(true))
+        case .isOn:
+          return .send(.set(\.isOn, true))
+        }
+      }
+    }
+  }
 #endif