Add toolbar and placed toolbar items

Author: colemancda

AndroidSwiftUICore/Sources/AndroidSwiftUICore/Toolbar.swift

@@ -0,0 +1,83 @@
+//
+//  Toolbar.swift
+//  AndroidSwiftUICore
+//
+//  Toolbar items are views, not data, so — unlike `navigationTitle` — they can't
+//  ride to the navigation chrome through the title sink. They travel as hidden
+//  children of the screen node instead (the mechanism sheets and alerts use),
+//  each tagged with its placement, and the interpreter lifts them into the bar.
+//
+
+/// Where a toolbar item sits in the navigation chrome.
+public enum ToolbarItemPlacement: String, Sendable {
+    case automatic
+    case navigationBarLeading
+    case navigationBarTrailing
+    /// Replaces the screen's title.
+    case principal
+    case bottomBar
+}
+
+/// A single positioned toolbar entry.
+public struct ToolbarItem<Content: View>: View {
+
+    internal let placement: ToolbarItemPlacement
+    internal let content: Content
+
+    public init(
+        placement: ToolbarItemPlacement = .automatic,
+        @ViewBuilder content: () -> Content
+    ) {
+        self.placement = placement
+        self.content = content()
+    }
+
+    public typealias Body = Never
+}
+
+extension ToolbarItem: PrimitiveView {
+
+    public func _render(in context: ResolveContext) -> RenderNode {
+        RenderNode(
+            type: "ToolbarItem",
+            id: context.path,
+            props: ["placement": .string(placement.rawValue)],
+            children: Evaluator.resolveChildren(content, context.descending("content"))
+        )
+    }
+}
+
+public struct _ToolbarView<Content: View, Items: View>: View {
+    internal let content: Content
+    internal let items: Items
+    public typealias Body = Never
+}
+
+extension _ToolbarView: PrimitiveView {
+
+    public func _render(in context: ResolveContext) -> RenderNode {
+        var node = Evaluator.resolve(content, context.descending("content"))
+        let resolved = Evaluator.resolveChildren(items, context.descending("toolbar"))
+        for item in resolved {
+            if item.type == "ToolbarItem" {
+                node.children.append(item)
+            } else {
+                // a bare view in the builder is an automatically-placed item
+                node.children.append(RenderNode(
+                    type: "ToolbarItem",
+                    id: item.id + "/item",
+                    props: ["placement": .string(ToolbarItemPlacement.automatic.rawValue)],
+                    children: [item]
+                ))
+            }
+        }
+        node.props["hasToolbar"] = .bool(true)
+        return node
+    }
+}
+
+public extension View {
+    func toolbar<Items: View>(@ViewBuilder content: () -> Items) -> _ToolbarView<Self, Items> {
+        _ToolbarView(content: self, items: content())
+    }
+}