added environment system

Author: sliemeobn

Sources/Elementary/Core/Environment.swift

@@ -0,0 +1,59 @@
+@propertyWrapper
+public struct Environment<T: Sendable>: Sendable {
+    enum _Storage {
+        case taskLocal(TaskLocal<T>)
+        case optionalTaskLocal(TaskLocal<T?>)
+    }
+
+    var storage: _Storage
+
+    public init(requiring taskLocal: TaskLocal<T?>) {
+        storage = .optionalTaskLocal(taskLocal)
+    }
+
+    public init(_ taskLocal: TaskLocal<T>) {
+        storage = .taskLocal(taskLocal)
+    }
+
+    public var wrappedValue: T {
+        switch storage {
+        case let .taskLocal(taskLocal): return taskLocal.wrappedValue
+        case let .optionalTaskLocal(taskLocal):
+            guard let value = taskLocal.wrappedValue else {
+                fatalError("No value set for \(T.self) in \(taskLocal)")
+            }
+
+            return value
+        }
+    }
+}
+
+public extension HTML {
+    func environment<T: Sendable>(_ taskLocal: TaskLocal<T>, _ value: T) -> _ModifiedTaskLocal<T, Self> {
+        _ModifiedTaskLocal(wrappedContent: self, taskLocal: taskLocal, value: value)
+    }
+}
+
+public struct _ModifiedTaskLocal<T: Sendable, Content: HTML>: HTML {
+    public typealias Tag = Content.Tag
+
+    var wrappedContent: Content
+    var taskLocal: TaskLocal<T>
+    var value: T
+
+    @_spi(Rendering)
+    public static func _render<Renderer>(_ html: consuming _ModifiedTaskLocal<T, Content>, into renderer: inout Renderer, with context: consuming _RenderingContext) where Renderer: _HTMLRendering {
+        html.taskLocal.withValue(html.value) {
+            Content._render(html.wrappedContent, into: &renderer, with: context)
+        }
+    }
+
+    @_spi(Rendering)
+    public static func _render<Renderer>(_ html: consuming Self, into renderer: inout Renderer, with context: consuming _RenderingContext) async throws where Renderer: _AsyncHTMLRendering {
+        try await html.taskLocal.withValue(html.value) {
+            try await Content._render(html.wrappedContent, into: &renderer, with: context)
+        }
+    }
+}
+
+extension _ModifiedTaskLocal: Sendable where Content: Sendable {}

Tests/ElementaryTests/EnvironmentRenderingTests.swift

@@ -0,0 +1,52 @@
+import Elementary
+import XCTest
+
+final class EnvironmentRenderingTests: XCTestCase {
+    func testSetsEnvironment() async throws {
+        try await HTMLAssertEqual(
+            div {
+                MyNumber()
+                MyNumber()
+                    .environment(Values.$number, 1)
+                MyNumber()
+            },
+            "<div>010</div>"
+        )
+    }
+
+    func testGetsOptionalEnvironment() async throws {
+        try await HTMLAssertEqualAsyncOnly(
+            div {
+                MyDatabaseValue()
+                    .environment(Values.$database, Database())
+            },
+            "<div><p>Hello</p></div>"
+        )
+    }
+}
+
+struct MyNumber: HTML {
+    @Environment(Values.$number) var number
+
+    var content: some HTML {
+        "\(number)"
+    }
+}
+
+struct MyDatabaseValue: HTML {
+    @Environment(requiring: Values.$database) var database
+    var content: some HTML {
+        p {
+            await database.value
+        }
+    }
+}
+
+enum Values {
+    @TaskLocal static var number = 0
+    @TaskLocal static var database: Database?
+}
+
+actor Database {
+    var value: String = "Hello"
+}