Display a deprecation warning and fatal error when the top-level @Environment(\.viewEnvironment) is referenced (#319)

Display a deprecation warning and fatal error when the top-level
`@Environment(\.viewEnvironment)` is referenced, to enforce people
reference a sub-property. This ensures proper SwiftUI view invalidation.

Author: kyleve

ViewEnvironment/Sources/EnvironmentValues+ViewEnvironment.swift

@@ -29,4 +29,26 @@ extension EnvironmentValues {
     }
 }
 
+extension Environment where Value == ViewEnvironment {
+    @available(
+        *,
+        deprecated,
+        message:
+        """
+        Please do not create an `@Environment` property that references the top-level `viewEnvironment`: \
+        it will break SwiftUI's automatic invalidation when any part of the `ViewEnvironment` changes. \
+        Instead, reference your relevant sub-property, eg `@Environment(\\.viewEnvironment.myProperty)`.
+        """
+    )
+    @inlinable public init(_ keyPath: KeyPath<EnvironmentValues, Value>) {
+        fatalError(
+            """
+            Please do not create an `@Environment` property that references the top-level `viewEnvironment`: \
+            it will break SwiftUI's automatic invalidation when any part of the `ViewEnvironment` changes. \
+            Instead, reference your relevant sub-property, eg `@Environment(\\.viewEnvironment.myProperty)`.
+            """
+        )
+    }
+}
+
 #endif

WorkflowSwiftUI/Tests/ObservableScreenTests.swift

@@ -39,6 +39,13 @@ private struct TestKey: ViewEnvironmentKey {
     static var defaultValue: Int = 0
 }
 
+extension ViewEnvironment {
+    fileprivate var testKey: Int {
+        get { self[TestKey.self] }
+        set { self[TestKey.self] = newValue }
+    }
+}
+
 @ObservableState
 private struct MyState {
     var emittedValue: TestKey.Value?
@@ -62,14 +69,14 @@ private struct TestKeyEmittingScreen: ObservableScreen {
     }
 
     struct ContentView: View {
-        @Environment(\.viewEnvironment)
-        var viewEnvironment: ViewEnvironment
+        @Environment(\.viewEnvironment.testKey)
+        var testValue: Int
 
         var store: Store<Model>
 
         var body: some View {
             WithPerceptionTracking {
-                let _ = { store.emittedValue = viewEnvironment[TestKey.self] }()
+                let _ = { store.emittedValue = testValue }()
                 Color.clear
                     .frame(width: 1, height: 1)
             }

WorkflowSwiftUIExperimental/Tests/SwiftUIScreenTests.swift

@@ -84,6 +84,13 @@ private struct TestKey: ViewEnvironmentKey {
     static var defaultValue: Int = 0
 }
 
+extension ViewEnvironment {
+    fileprivate var testKey: Int {
+        get { self[TestKey.self] }
+        set { self[TestKey.self] = newValue }
+    }
+}
+
 private struct ContentScreen: SwiftUIScreen {
     let sizingOptions: SwiftUIScreenSizingOptions
 
@@ -103,13 +110,14 @@ private struct TestKeyEmittingScreen: SwiftUIScreen {
     }
 
     struct ContentView: View {
-        @Environment(\.viewEnvironment)
-        var viewEnvironment: ViewEnvironment
+        @Environment(\.viewEnvironment.testKey)
+        var testValue: Int
 
         var onTestKeyEmission: (TestKey.Value) -> Void
 
         var body: some View {
-            let _ = onTestKeyEmission(viewEnvironment[TestKey.self])
+            let _ = onTestKeyEmission(testValue)
+
             Color.clear
                 .frame(width: 1, height: 1)
         }