Add @EnvironmentObject

Package.resolved

@@ -10,6 +10,15 @@
           "version": null
         }
       },
+      {
+        "package": "OpenCombine",
+        "repositoryURL": "https://github.com/MaxDesiatov/OpenCombine.git",
+        "state": {
+          "branch": "wasi",
+          "revision": "4fed049b0ab7095d4d26247ef958d3f6e361c569",
+          "version": null
+        }
+      },
       {
         "package": "Runtime",
         "repositoryURL": "https://github.com/MaxDesiatov/Runtime.git",

Package.swift

@@ -26,6 +26,7 @@ let package = Package(
     // .package(url: /* package url */, from: "1.0.0"),
     .package(url: "https://github.com/kateinoigakukun/JavaScriptKit.git", .revision("47f2bb1")),
     .package(url: "https://github.com/MaxDesiatov/Runtime.git", .branch("wasi-build")),
+    .package(url: "https://github.com/MaxDesiatov/OpenCombine.git", .branch("wasi")),
   ],
   targets: [
     // Targets are the basic building blocks of a package. A target can define
@@ -34,7 +35,7 @@ let package = Package(
     // in packages which this package depends on.
     .target(
       name: "TokamakCore",
-      dependencies: ["Runtime"]
+      dependencies: ["Runtime", "OpenCombine"]
     ),
     .target(
       name: "TokamakDemo",

Sources/TokamakCore/Environment/Environment.swift

@@ -22,7 +22,7 @@ protocol EnvironmentReader {
     case value(Value)
   }
 
-  var content: Environment<Value>.Content
+  var content: Content
   let keyPath: KeyPath<EnvironmentValues, Value>
   public init(_ keyPath: KeyPath<EnvironmentValues, Value>) {
     content = .keyPath(keyPath)

Sources/TokamakCore/Environment/EnvironmentObject.swift

@@ -0,0 +1,77 @@
+// 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 7/7/20.
+//
+
+import OpenCombine
+
+protocol EnvironmentWriter {
+  func subscribe(_ closure: @escaping () -> ())
+}
+
+@propertyWrapper public struct EnvironmentObject<ObjectType>: EnvironmentReader, EnvironmentWriter where ObjectType: ObservableObject {
+  @dynamicMemberLookup public struct Wrapper {
+    internal let root: ObjectType
+    public subscript<Subject>(dynamicMember keyPath: ReferenceWritableKeyPath<ObjectType, Subject>) -> Binding<Subject> {
+      Binding {
+        root[keyPath: keyPath]
+      } set: {
+        root[keyPath: keyPath] = $0
+      }
+    }
+  }
+
+  var _store: ObjectType?
+  var _seed: Int = 0
+
+  mutating func setContent(from values: EnvironmentValues) {
+    _store = values[ObjectIdentifier(ObjectType.self)]
+  }
+
+  func subscribe(_ closure: @escaping () -> ()) {
+    _ = _store?.objectWillChange.sink { _ in
+      print("EnvironmentObject changed!")
+      closure()
+    }
+  }
+
+  public var wrappedValue: ObjectType {
+    guard let store = _store else { error() }
+    return store
+  }
+
+  public var projectedValue: Wrapper {
+    guard let store = _store else { error() }
+    return Wrapper(root: store)
+  }
+
+  func error() -> Never {
+    fatalError("No ObservableObject found for type \(ObjectType.self)")
+  }
+
+  public init() {}
+}
+
+extension ObservableObject {
+  static var environmentStore: WritableKeyPath<EnvironmentValues, Self?> {
+    \.[ObjectIdentifier(self)]
+  }
+}
+
+extension View {
+  public func environmentObject<B>(_ bindable: B) -> some View where B: ObservableObject {
+    environment(B.environmentStore, bindable)
+  }
+}

Sources/TokamakCore/Environment/EnvironmentValues.swift

@@ -12,6 +12,8 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+import OpenCombine
+
 public struct EnvironmentValues: CustomStringConvertible {
   public var description: String {
     String(describing: values)
@@ -32,4 +34,13 @@ public struct EnvironmentValues: CustomStringConvertible {
       values[ObjectIdentifier(key)] = newValue
     }
   }
+
+  subscript<B>(bindable: ObjectIdentifier) -> B? where B: ObservableObject {
+    get {
+      values[bindable] as? B
+    }
+    set {
+      values[bindable] = newValue
+    }
+  }
 }

Sources/TokamakCore/MountedViews/MountedView.swift

@@ -68,6 +68,17 @@ extension View {
         try! prop.set(value: wrapper, on: &extractedView)
         // swiftlint:enable force_cast
       }
+
+      // Setup onEnvironmentChanged for all @EnvironmentObject
+      for prop in viewInfo.properties.filter({ $0.type is EnvironmentWriter.Type }) {
+        // swiftlint:disable force_cast
+        let wrapper = try! prop.get(from: any.view) as! EnvironmentWriter
+        wrapper.subscribe {
+          print("Environment changed (received on reconciler)")
+        }
+        // swiftlint:enable force_cast
+      }
+
       // Set the extractedView back on the AnyView after modification
       let anyViewInfo = try! typeInfo(of: AnyView.self)
       try! anyViewInfo.property(named: "view").set(value: extractedView, on: &injectableView)

Sources/TokamakCore/StackReconciler.swift

@@ -67,6 +67,8 @@ public final class StackReconciler<R: Renderer> {
     // swiftlint:disable force_try
     let info = try! typeInfo(of: compositeView.view.type)
     let stateProperties = info.properties.filter { $0.type is ValueStorage.Type }
+    let environmentObjects = info.properties.filter { $0.type is EnvironmentReader.Type }
+    print(environmentObjects)
 
     for (id, stateProperty) in stateProperties.enumerated() {
       // `ValueStorage` properties were already filtered out, so safe to assume the value's type

Sources/TokamakDOM/Environment/Environment.swift

@@ -18,3 +18,4 @@
 import TokamakCore
 
 public typealias Environment = TokamakCore.Environment
+public typealias EnvironmentObject = TokamakCore.EnvironmentObject

Sources/TokamakDemo/EnvironmentDemo.swift

@@ -18,17 +18,33 @@
 #if canImport(SwiftUI)
 import SwiftUI
 #else
+import OpenCombine
 import TokamakDOM
 #endif
 
+class TestEnvironment: ObservableObject {
+  var envTest = "Hello, world!" {
+    willSet {
+      print(newValue)
+      objectWillChange.send()
+    }
+  }
+
+  let objectWillChange = ObservableObjectPublisher()
+
+  init() {}
+}
+
 struct EnvironmentDemo: View {
   @Environment(\.font) var font: Font?
+  @EnvironmentObject var testEnv: TestEnvironment
 
   var body: some View {
-    if let font = font {
-      return Text("\(String(describing: font))")
-    } else {
-      return Text("`font` environment not set.")
+    VStack {
+      Text(font == nil ? "`font` environment not set." : "\(String(describing: font!))")
+      Button(testEnv.envTest) {
+        testEnv.envTest = "EnvironmentObject modified."
+      }
     }
   }
 }

Sources/TokamakDemo/TokamakDemo.swift

@@ -61,5 +61,6 @@ struct TokamakDemoView: View {
         }
       }
     }
+    .environmentObject(TestEnvironment())
   }
 }

Sources/TokamakDemo/main.swift

@@ -13,6 +13,7 @@
 // limitations under the License.
 
 import JavaScriptKit
+import OpenCombine
 import TokamakDOM
 
 let document = JSObjectRef.global.document.object!