Implement Environment (#135)

* Environment impl

* Fix line lengths

* Danger and review fixes

* rename _modifyEnvironment to modifyEnvironment

Sources/TokamakCore/Environment/Environment.swift

@@ -12,15 +12,25 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-@propertyWrapper public struct Environment<Value> {
+protocol EnvironmentReader {
+  mutating func setContent(from values: EnvironmentValues)
+}
+
+@propertyWrapper public struct Environment<Value>: EnvironmentReader {
   enum Content {
     case keyPath(KeyPath<EnvironmentValues, Value>)
     case value(Value)
   }
 
   var content: Environment<Value>.Content
+  let keyPath: KeyPath<EnvironmentValues, Value>
   public init(_ keyPath: KeyPath<EnvironmentValues, Value>) {
     content = .keyPath(keyPath)
+    self.keyPath = keyPath
+  }
+
+  mutating func setContent(from values: EnvironmentValues) {
+    content = .value(values[keyPath: keyPath])
   }
 
   public var wrappedValue: Value {

Sources/TokamakCore/Environment/EnvironmentKey.swift

@@ -14,12 +14,14 @@
 
 public protocol EnvironmentKey {
   associatedtype Value
-  static var defaultValue: Self.Value { get }
+  static var defaultValue: Value { get }
 }
 
-public struct _EnvironmentKeyWritingModifier<Value>: ViewModifier {
+protocol EnvironmentModifier {
-  public typealias Body = Never
+  func modifyEnvironment(_ values: inout EnvironmentValues)
+}
 
+public struct _EnvironmentKeyWritingModifier<Value>: ViewModifier, EnvironmentModifier {
   public let keyPath: WritableKeyPath<EnvironmentValues, Value>
   public let value: Value
 
@@ -27,6 +29,14 @@ public struct _EnvironmentKeyWritingModifier<Value>: ViewModifier {
     self.keyPath = keyPath
     self.value = value
   }
+
+  public func body(content: Content) -> some View {
+    content
+  }
+
+  func modifyEnvironment(_ values: inout EnvironmentValues) {
+    values[keyPath: keyPath] = value
+  }
 }
 
 extension View {

Sources/TokamakCore/MountedComponents/MountedCompositeView.swift

@@ -31,9 +31,12 @@ final class MountedCompositeView<R: Renderer>: MountedView<R>, Hashable {
   private let parentTarget: R.TargetType
 
   var state = [Any]()
+  var environmentValues: EnvironmentValues
 
-  init(_ view: AnyView, _ parentTarget: R.TargetType) {
+  init(_ view: AnyView, _ parentTarget: R.TargetType,
+       _ environmentValues: EnvironmentValues) {
     self.parentTarget = parentTarget
+    self.environmentValues = environmentValues
 
     super.init(view)
   }
@@ -41,7 +44,8 @@ final class MountedCompositeView<R: Renderer>: MountedView<R>, Hashable {
   override func mount(with reconciler: StackReconciler<R>) {
     let childBody = reconciler.render(compositeView: self)
 
-    let child: MountedView<R> = childBody.makeMountedView(parentTarget)
+    let child: MountedView<R> = childBody.makeMountedView(parentTarget,
+                                                          environmentValues)
     mountedChildren = [child]
     child.mount(with: reconciler)
   }
@@ -58,7 +62,8 @@ final class MountedCompositeView<R: Renderer>: MountedView<R>, Hashable {
     switch (mountedChildren.last, reconciler.render(compositeView: self)) {
     // no mounted children, but children available now
     case let (nil, childBody):
-      let child: MountedView<R> = childBody.makeMountedView(parentTarget)
+      let child: MountedView<R> = childBody.makeMountedView(parentTarget,
+                                                            environmentValues)
       mountedChildren = [child]
       child.mount(with: reconciler)
 
@@ -81,7 +86,8 @@ final class MountedCompositeView<R: Renderer>: MountedView<R>, Hashable {
         // wrapper, then mount a new one with the new `childBody`
         wrapper.unmount(with: reconciler)
 
-        let child: MountedView<R> = childBody.makeMountedView(parentTarget)
+        let child: MountedView<R> = childBody.makeMountedView(parentTarget,
+                                                              environmentValues)
         mountedChildren = [child]
         child.mount(with: reconciler)
       }

Sources/TokamakCore/MountedComponents/MountedHostView.swift

@@ -31,9 +31,13 @@ public final class MountedHostView<R: Renderer>: MountedView<R> {
   /// Target of this host view supplied by a renderer after mounting has completed.
   private var target: R.TargetType?
 
+  private let environmentValues: EnvironmentValues
+
   init(_ view: AnyView,
-       _ parentTarget: R.TargetType) {
+       _ parentTarget: R.TargetType,
+       _ environmentValues: EnvironmentValues) {
     self.parentTarget = parentTarget
+    self.environmentValues = environmentValues
 
     super.init(view)
   }
@@ -48,7 +52,9 @@ public final class MountedHostView<R: Renderer>: MountedView<R> {
 
     guard !view.children.isEmpty else { return }
 
-    mountedChildren = view.children.map { $0.makeMountedView(target) }
+    mountedChildren = view.children.map {
+      $0.makeMountedView(target, environmentValues)
+    }
     mountedChildren.forEach { $0.mount(with: reconciler) }
   }
 
@@ -81,7 +87,9 @@ public final class MountedHostView<R: Renderer>: MountedView<R> {
 
     // if no existing children then mount all new children
     case (true, false):
-      mountedChildren = childrenViews.map { $0.makeMountedView(target) }
+      mountedChildren = childrenViews.map {
+        $0.makeMountedView(target, environmentValues)
+      }
       mountedChildren.forEach { $0.mount(with: reconciler) }
 
     // if both arrays have items then reconcile by types and keys
@@ -99,7 +107,7 @@ public final class MountedHostView<R: Renderer>: MountedView<R> {
           newChild = child
         } else {
           child.unmount(with: reconciler)
-          newChild = firstChild.makeMountedView(target)
+          newChild = firstChild.makeMountedView(target, environmentValues)
           newChild.mount(with: reconciler)
         }
         newChildren.append(newChild)
@@ -118,7 +126,7 @@ public final class MountedHostView<R: Renderer>: MountedView<R> {
         // mount remaining views
         for firstChild in childrenViews {
           let newChild: MountedView<R> =
-            firstChild.makeMountedView(target)
+            firstChild.makeMountedView(target, environmentValues)
           newChild.mount(with: reconciler)
           newChildren.append(newChild)
         }

Sources/TokamakCore/MountedComponents/MountedView.swift

@@ -36,15 +36,16 @@ public class MountedView<R: Renderer> {
 }
 
 extension View {
-  func makeMountedView<R: Renderer>(_ parentTarget: R.TargetType)
+  func makeMountedView<R: Renderer>(_ parentTarget: R.TargetType,
+                                    _ environmentValues: EnvironmentValues)
     -> MountedView<R> {
     let anyView = self as? AnyView ?? AnyView(self)
     if anyView.type == EmptyView.self {
       return MountedNull(anyView)
     } else if anyView.bodyType == Never.self && !(anyView.type is ViewDeferredToRenderer.Type) {
-      return MountedHostView(anyView, parentTarget)
+      return MountedHostView(anyView, parentTarget, environmentValues)
     } else {
-      return MountedCompositeView(anyView, parentTarget)
+      return MountedCompositeView(anyView, parentTarget, environmentValues)
     }
   }
 }

Sources/TokamakCore/StackReconciler.swift

@@ -35,7 +35,7 @@ public final class StackReconciler<R: Renderer> {
     self.scheduler = scheduler
     rootTarget = target
 
-    rootView = view.makeMountedView(target)
+    rootView = view.makeMountedView(target, EnvironmentValues())
 
     rootView.mount(with: self)
   }
@@ -88,6 +88,28 @@ public final class StackReconciler<R: Renderer> {
       }
       try! stateProperty.set(value: state, on: &compositeView.view.view)
     }
+
+    let viewInfo = try! typeInfo(of: compositeView.view.type)
+    if viewInfo
+      .genericTypes
+      .filter({ $0 is EnvironmentModifier.Type }).count > 0 {
+      // Apply Environment changes:
+      if let modifier = try? viewInfo
+        .property(named: "modifier")
+        .get(from: compositeView.view.view) as? EnvironmentModifier {
+        modifier.modifyEnvironment(&compositeView.environmentValues)
+      }
+    }
+
+    // Inject @Environment values
+    // In the future we can also inject @EnvironmentObject values
+    for prop in viewInfo.properties.filter({ $0.type is EnvironmentReader.Type }) {
+      // swiftlint:disable force_cast
+      var wrapper = try! prop.get(from: compositeView.view.view) as! EnvironmentReader
+      wrapper.setContent(from: compositeView.environmentValues)
+      try! prop.set(value: wrapper, on: &compositeView.view.view)
+      // swiftlint:enable force_cast
+    }
     // swiftlint:enable force_try
 
     let result = compositeView.view.bodyClosure(compositeView.view.view)

Sources/TokamakDOM/Environment/Environment.swift

@@ -0,0 +1,20 @@
+// Copyright 2020 Tokamak contributors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+//  Created by Carson Katri on 6/30/20.
+//
+
+import TokamakCore
+
+public typealias Environment = TokamakCore.Environment

Sources/TokamakDemo/EnvironmentDemo.swift

@@ -0,0 +1,30 @@
+// Copyright 2019-2020 Tokamak contributors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+//  Created by Carson Katri on 6/30/20.
+//
+
+import TokamakDOM
+
+struct EnvironmentDemo: View {
+  @Environment(\.font) var font: Font?
+
+  var body: some View {
+    if let font = font {
+      return Text("\(font)")
+    } else {
+      return Text("`font` environment not set.")
+    }
+  }
+}

Sources/TokamakDemo/main.swift

@@ -55,6 +55,8 @@ let renderer = DOMRenderer(
       SpacerDemo()
       Spacer()
       Text("Forced to bottom.")
+      EnvironmentDemo()
+        .font(.system(size: 21))
     }
   },
   div