Support meta tags in StaticHTMLRenderer

Sources/TokamakCore/MountedViews/MountedCompositeView.swift

@@ -78,9 +78,6 @@ final class MountedCompositeView<R: Renderer>: MountedCompositeElement<R> {
 
       if let preferenceModifier = self.view.view as? _PreferenceWritingViewProtocol {
         self.view = preferenceModifier.modifyPreferenceStore(&self.preferenceStore)
-        if let parent = parent {
-          parent.preferenceStore.merge(with: self.preferenceStore)
-        }
       }
 
       if let preferenceReader = self.view.view as? _PreferenceReadingViewProtocol {

Sources/TokamakCore/MountedViews/MountedElement.swift

@@ -94,13 +94,9 @@ public class MountedElement<R: Renderer> {
 
   public internal(set) var environmentValues: EnvironmentValues
 
-  weak var parent: MountedElement<R>?
-  /// `didSet` on this field propagates the preference changes up the view tree.
-  var preferenceStore: _PreferenceStore = .init() {
-    didSet {
-      parent?.preferenceStore.merge(with: preferenceStore)
-    }
-  }
+  private(set) weak var parent: MountedElement<R>?
+
+  var preferenceStore: _PreferenceStore = .init()
 
   public internal(set) var viewTraits: _ViewTraitStore
 
@@ -110,6 +106,7 @@ public class MountedElement<R: Renderer> {
     self.environmentValues = environmentValues
     viewTraits = .init()
     updateEnvironment()
+    connectParentPreferenceStore()
   }
 
   init(_ scene: _AnyScene, _ environmentValues: EnvironmentValues, _ parent: MountedElement<R>?) {
@@ -118,6 +115,7 @@ public class MountedElement<R: Renderer> {
     self.environmentValues = environmentValues
     viewTraits = .init()
     updateEnvironment()
+    connectParentPreferenceStore()
   }
 
   init(
@@ -131,6 +129,7 @@ public class MountedElement<R: Renderer> {
     self.environmentValues = environmentValues
     self.viewTraits = viewTraits
     updateEnvironment()
+    connectParentPreferenceStore()
   }
 
   func updateEnvironment() {
@@ -145,6 +144,10 @@ public class MountedElement<R: Renderer> {
     }
   }
 
+  func connectParentPreferenceStore() {
+    preferenceStore.parent = parent?.preferenceStore
+  }
+
   /// You must call `super.prepareForMount` before all other mounting work.
   func prepareForMount(with transaction: Transaction) {
     // `GroupView`'s don't really mount, so let their children transition if the group can.

Sources/TokamakCore/Preferences/PreferenceKey.swift

@@ -48,10 +48,12 @@ public extension _PreferenceValue {
   }
 }
 
-public struct _PreferenceStore {
+public final class _PreferenceStore {
   /// The backing values of the `_PreferenceStore`.
   private var values: [String: Any]
 
+  weak var parent: _PreferenceStore?
+
   public init(values: [String: Any] = [:]) {
     self.values = values
   }
@@ -63,23 +65,12 @@ public struct _PreferenceStore {
       ?? _PreferenceValue(valueList: [Key.defaultValue])
   }
 
-  public mutating func insert<Key>(_ value: Key.Value, forKey key: Key.Type = Key.self)
+  public func insert<Key>(_ value: Key.Value, forKey key: Key.Type = Key.self)
     where Key: PreferenceKey
   {
     let previousValues = self.value(forKey: key).valueList
     values[String(reflecting: key)] = _PreferenceValue<Key>(valueList: previousValues + [value])
-  }
-
-  public mutating func merge(with other: Self) {
-    self = merging(with: other)
-  }
-
-  public func merging(with other: Self) -> Self {
-    var result = values
-    for (key, value) in other.values {
-      result[key] = value
-    }
-    return .init(values: result)
+    parent?.insert(value, forKey: key)
   }
 }
 

Sources/TokamakCore/StackReconciler.swift

@@ -58,6 +58,12 @@ public final class StackReconciler<R: Renderer> {
    */
   public let rootTarget: R.TargetType
 
+  /** A root renderer's main preference store.
+   */
+  public var preferenceStore: _PreferenceStore {
+    rootElement.preferenceStore
+  }
+
   /** A root of the mounted elements tree to which all other mounted elements are attached to.
    */
   private let rootElement: MountedElement<R>

Sources/TokamakCore/Views/Containers/Group.swift

@@ -19,7 +19,7 @@ public struct Group<Content> {
   }
 }
 
-extension Group: _PrimitiveView & View where Content: View {}
+extension Group: _PrimitiveView, View where Content: View {}
 
 extension Group: ParentView where Content: View {
   @_spi(TokamakCore)

Sources/TokamakStaticHTML/App.swift

@@ -24,7 +24,7 @@ public extension App {
   }
 
   static func _setTitle(_ title: String) {
-    StaticHTMLRenderer.title = title
+    // no-op: use Title view
   }
 
   var _phasePublisher: AnyPublisher<ScenePhase, Never> {

Sources/TokamakStaticHTML/Preferences/Preferences.swift

@@ -0,0 +1,37 @@
+// Copyright 2022 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 Andrew Barba on 5/20/22.
+//
+
+import TokamakCore
+
+public struct HTMLTitlePreferenceKey: PreferenceKey {
+  public static var defaultValue: String = ""
+
+  public static func reduce(value: inout String, nextValue: () -> String) {
+    value = nextValue()
+  }
+}
+
+public struct HTMLMetaPreferenceKey: PreferenceKey {
+  public static var defaultValue: [HTMLMeta.MetaTag] = []
+
+  public static func reduce(
+    value: inout [HTMLMeta.MetaTag],
+    nextValue: () -> [HTMLMeta.MetaTag]
+  ) {
+    value += nextValue()
+  }
+}

Sources/TokamakStaticHTML/StaticHTMLRenderer.swift

@@ -58,18 +58,40 @@ struct HTMLBody: AnyHTML {
   ]
 }
 
+extension HTMLMeta.MetaTag {
+  func outerHTML() -> String {
+    switch self {
+    case let .charset(charset):
+      return #"<meta charset="\#(charset)">"#
+    case let .name(name, content):
+      return #"<meta name="\#(name)" content="\#(content)">"#
+    case let .property(property, content):
+      return #"<meta property="\#(property)" content="\#(content)">"#
+    case let .httpEquiv(httpEquiv, content):
+      return #"<meta http-equiv="\#(httpEquiv)" content="\#(content)">"#
+    }
+  }
+}
+
 public final class StaticHTMLRenderer: Renderer {
   private var reconciler: StackReconciler<StaticHTMLRenderer>?
 
   var rootTarget: HTMLTarget
 
-  static var title: String = ""
+  var title: String {
+    reconciler?.preferenceStore.value(forKey: HTMLTitlePreferenceKey.self).value ?? ""
+  }
+
+  var meta: [HTMLMeta.MetaTag] {
+    reconciler?.preferenceStore.value(forKey: HTMLMetaPreferenceKey.self).value ?? []
+  }
 
   public func render(shouldSortAttributes: Bool = false) -> String {
     """
     <html>
     <head>
-      <title>\(Self.title)</title>
+      <title>\(title)</title>
+      \(meta.map { $0.outerHTML() }.joined(separator: "\n  "))
       <style>
         \(tokamakStyles)
       </style>

Sources/TokamakStaticHTML/Views/Head/Meta.swift

@@ -0,0 +1,83 @@
+// Copyright 2022 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 Andrew Barba on 5/20/22.
+//
+
+import TokamakCore
+
+public struct HTMLMeta: View {
+  public enum MetaTag: Equatable, Hashable {
+    case charset(_ charset: String)
+    case name(_ name: String, content: String)
+    case property(_ property: String, content: String)
+    case httpEquiv(_ httpEquiv: String, content: String)
+  }
+
+  var meta: MetaTag
+
+  public init(_ value: MetaTag) {
+    meta = value
+  }
+
+  public init(charset: String) {
+    meta = .charset(charset)
+  }
+
+  public init(name: String, content: String) {
+    meta = .name(name, content: content)
+  }
+
+  public init(property: String, content: String) {
+    meta = .property(property, content: content)
+  }
+
+  public init(httpEquiv: String, content: String) {
+    meta = .httpEquiv(httpEquiv, content: content)
+  }
+
+  public var body: some View {
+    EmptyView()
+      .preference(key: HTMLMetaPreferenceKey.self, value: [meta])
+  }
+}
+
+public extension View {
+  func htmlMeta(_ value: HTMLMeta.MetaTag) -> some View {
+    htmlMeta(.init(value))
+  }
+
+  func htmlMeta(charset: String) -> some View {
+    htmlMeta(.init(charset: charset))
+  }
+
+  func htmlMeta(name: String, content: String) -> some View {
+    htmlMeta(.init(name: name, content: content))
+  }
+
+  func htmlMeta(property: String, content: String) -> some View {
+    htmlMeta(.init(property: property, content: content))
+  }
+
+  func htmlMeta(httpEquiv: String, content: String) -> some View {
+    htmlMeta(.init(httpEquiv: httpEquiv, content: content))
+  }
+
+  func htmlMeta(_ meta: HTMLMeta) -> some View {
+    Group {
+      self
+      meta
+    }
+  }
+}

Sources/TokamakStaticHTML/Views/Head/Title.swift

@@ -0,0 +1,44 @@
+// Copyright 2022 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 Andrew Barba on 5/20/22.
+//
+
+import TokamakCore
+
+public struct HTMLTitle: View {
+  var title: String
+
+  public init(_ title: String) {
+    self.title = title
+  }
+
+  public var body: some View {
+    EmptyView()
+      .preference(key: HTMLTitlePreferenceKey.self, value: title)
+  }
+}
+
+public extension View {
+  func htmlTitle(_ title: String) -> some View {
+    htmlTitle(.init(title))
+  }
+
+  func htmlTitle(_ title: HTMLTitle) -> some View {
+    Group {
+      self
+      title
+    }
+  }
+}