From 65b050308705c56d998371ec90a6ff793c148aa1 Mon Sep 17 00:00:00 2001
From: Brandon Williams <mbrandonw@hey.com>
Date: Tue, 12 Nov 2024 09:52:15 -0500
Subject: [PATCH] Fix exclusive access problem in preview traits.

---
 .../Dependencies/Traits/PreviewTrait.swift    |  4 +++-
 .../PreviewTraitsTests.swift                  | 21 +++++++++++++++++++
 2 files changed, 24 insertions(+), 1 deletion(-)
 create mode 100644 Tests/DependenciesTests/PreviewTraitsTests.swift

diff --git a/Sources/Dependencies/Traits/PreviewTrait.swift b/Sources/Dependencies/Traits/PreviewTrait.swift
index ff137ce0..adbe823c 100644
--- a/Sources/Dependencies/Traits/PreviewTrait.swift
+++ b/Sources/Dependencies/Traits/PreviewTrait.swift
@@ -47,7 +47,9 @@
     public static func dependencies(
       _ updateValuesForPreview: (inout DependencyValues) -> Void
     ) -> PreviewTrait {
-      updateValuesForPreview(&previewValues)
+      var copy = previewValues
+      defer { previewValues = copy }
+      updateValuesForPreview(&copy)
       return PreviewTrait()
     }
   }
diff --git a/Tests/DependenciesTests/PreviewTraitsTests.swift b/Tests/DependenciesTests/PreviewTraitsTests.swift
new file mode 100644
index 00000000..f78f02fd
--- /dev/null
+++ b/Tests/DependenciesTests/PreviewTraitsTests.swift
@@ -0,0 +1,21 @@
+#if os(iOS) || os(macOS) || os(tvOS) || os(watchOS)
+import Dependencies
+import Testing
+import SwiftUI
+
+@Suite
+@MainActor
+struct PreviewTraitsTests {
+  @Test
+  @available(iOS 18, macOS 15, tvOS 18, watchOS 11, visionOS 2, *)
+  func dependency() {
+    _ = PreviewTrait.dependency(\.date.now, Date(timeIntervalSince1970: 1234567890))
+    withDependencies {
+      $0.context = .preview
+    } operation: {
+      @Dependency(\.date.now) var now
+      #expect(now == Date(timeIntervalSince1970: 1234567890))
+    }
+  }
+}
+#endif