Better document explicit id with scoped ForEach (#2784)

`ForEachStore` implicitly used `id: \.state.id` under the hood, so a
naive migration to `ForEach` might miss this detail. Let's be more
explicit in our documentation and migration guide to avoid this issue.

In the future it might be possible to address better in the library
itself, but for now the requirement for stores to be identifiable for
other forms of navigation means allowing for this.

Sources/ComposableArchitecture/Documentation.docc/Articles/MigrationGuides/MigratingTo1.7.md

@@ -204,27 +204,33 @@ struct Feature {
 Then you would have made use of ``ForEachStore`` in the view like this:
 
 ```swift
-ForEachStore(store.scope(state: \.rows, action: \.rows)) { childStore in
+ForEachStore(
+  store.scope(state: \.rows, action: \.rows)
+) { childStore in
   ChildView(store: childStore)
 }
 ```
 
 This can now be updated to use the vanilla `ForEach` view in SwiftUI, along with 
-``Store/scope(state:action:)-1nelp``:
+``Store/scope(state:action:)-1nelp``, identified by the state of each row:
 
 ```swift
-ForEach(store.scope(state: \.rows, action: \.rows)) { childStore in
+ForEach(
+  store.scope(state: \.rows, action: \.rows), id: \.state.id
+) { childStore in
   ChildView(store: childStore)
 }
 ```
 
-If your usage of `ForEachStore` relied on the identity of the state of each row (_e.g._, the state's
-`id` is also associated with a selection binding), you must explicitly use the `id` parameter:
+If your usage of `ForEachStore` did not depend on the identity of the state of each row (_e.g._, the
+state's `id` is not associated with a selection binding), you can omit the `id` parameter, as the
+`Store` type is identifiable by its object identity:
 
 ```diff
  ForEach(
-   store.scope(state: \.rows, action: \.rows),
-+  id: \.state.id
+-  store.scope(state: \.rows, action: \.rows),
+-  id: \.state.id,
++  store.scope(state: \.rows, action: \.rows)
  ) { childStore in
    ChildView(store: childStore)
  }

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

@@ -71,7 +71,7 @@ This means that even if you wrap the body of the view in `WithPerceptionTracking
 
 ```swift
 WithPerceptionTracking {
-  ForEach(store.scope(state: \.rows, action: \.rows) { store in
+  ForEach(store.scope(state: \.rows, action: \.rows), id: \.state.id) { store in
     Text(store.title)
   }
 }
@@ -84,7 +84,7 @@ The fix for this is to wrap the content of the trailing closure in another `With
 
 ```swift
 WithPerceptionTracking {
-  ForEach(store.scope(state: \.rows, action: \.rows) { store in
+  ForEach(store.scope(state: \.rows, action: \.rows), id: \.state.id) { store in
     WithPerceptionTracking {
       Text(store.title)
     }

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

@@ -351,7 +351,7 @@ Another example is scoping to some collection of a child domain in order to use
 ``ForEachStore``:
 
 ```swift
-ForEachStore(store.scope(state: \.rows, action: \.rows) { store in
+ForEachStore(store.scope(state: \.rows, action: \.rows)) { store in
   RowView(store: store)
 }
 ```

Sources/ComposableArchitecture/Observation/IdentifiedArray+Observation.swift

@@ -5,8 +5,8 @@
   extension Store where State: ObservableState {
     /// Scopes the store of an identified collection to a collection of stores.
     ///
-    /// This operator is most often used with SwiftUI's `ForEach` view. For example, suppose you have
-    /// a feature that contains an `IdentifiedArray` of child features like so:
+    /// This operator is most often used with SwiftUI's `ForEach` view. For example, suppose you
+    /// have a feature that contains an `IdentifiedArray` of child features like so:
     ///
     /// ```swift
     /// @Reducer
@@ -38,14 +38,28 @@
     ///
     ///   var body: some View {
     ///     List {
-    ///       ForEach(store.scope(state: \.rows, action: \.rows) { store in
+    ///       ForEach(store.scope(state: \.rows, action: \.rows), id: \.state.id) { store in
     ///         ChildView(store: store)
     ///       }
     ///     }
     ///   }
     /// }
     /// ```
     ///
+    /// > Tip: If you do not depend on the identity of the state of each row (_e.g._, the state's
+    /// > `id` is not associated with a selection binding), you can omit the `id` parameter, as the
+    /// > `Store` type is identifiable by its object identity:
+    /// >
+    /// > ```diff
+    /// >  ForEach(
+    /// > -  store.scope(state: \.rows, action: \.rows),
+    /// > -  id: \.state.id,
+    /// > +  store.scope(state: \.rows, action: \.rows)
+    /// >  ) { childStore in
+    /// >    ChildView(store: childStore)
+    /// >  }
+    /// > ```
+    ///
     /// - Parameters:
     ///   - state: A key path to an identified array of child state.
     ///   - action: A case key path to an identified child action.