fix(HitsList): remove race condition

Sources/InstantSearchCore/Searcher/AbstractSearcher.swift

@@ -125,7 +125,7 @@ open class AbstractSearcher<Service: SearchService>: Searcher, SequencerDelegate
 public extension AbstractSearcher {
   /// Search error composition encapsulating the error returned by the search service and the request for which this error occured
   struct RequestError: Error {
-    /// Request for which an error occured
+    /// Request for which an error occurred
     public let request: Request
 
     /// Error returned by the search service

Sources/InstantSearchSwiftUI/DataModel/HitsObservableController.swift

@@ -29,10 +29,13 @@ import InstantSearchTelemetry
     }
 
     public func reload() {
-      if let hitsSource = hitsSource, hitsSource.numberOfHits() > 0 {
-        hits = hitsSource.hits
-      } else {
-        hits = []
+      DispatchQueue.main.async { [weak self] in
+        guard let self = self else { return }
+        if let hitsSource = self.hitsSource, hitsSource.numberOfHits() > 0 {
+          self.hits = hitsSource.hits
+        } else {
+          self.hits = []
+        }
       }
     }
 

Sources/InstantSearchSwiftUI/View/HitsList.swift

@@ -52,7 +52,8 @@
     }
 
     private func row(atIndex index: Int) -> some View {
-      row(hitsObservable.hits[index], index).onAppear {
+      let hit = index < hitsObservable.hits.count ? hitsObservable.hits[index] : nil
+      return row(hit, index).onAppear {
         hitsObservable.notifyAppearanceOfHit(atIndex: index)
       }
     }

Tests/InstantSearchSwiftUITests/ObservableControllerTests.swift

@@ -5,7 +5,147 @@
 //  Created by Vladislav Fitc on 05/11/2021.
 //
 
+#if !InstantSearchCocoaPods
+  import InstantSearchCore
+#endif
+import AlgoliaSearchClient
 @testable import InstantSearchSwiftUI
 import XCTest
 
-class ObservableControllerTests: XCTestCase {}
+// MARK: - Test Helper
+
+struct TestRecord<Value: Codable>: Codable {
+  let objectID: ObjectID
+  let value: Value
+
+  init(_ value: Value, objectID: ObjectID = ObjectID(rawValue: UUID().uuidString)) {
+    self.value = value
+    self.objectID = objectID
+  }
+
+  static func withValue(_ value: Value) -> Self {
+    .init(value)
+  }
+}
+
+@available(iOS 13.0, OSX 10.15, tvOS 13.0, watchOS 6.0, *)
+class ObservableControllerTests: XCTestCase {
+
+  // MARK: - Basic Functionality Tests
+
+  func testInitialState() {
+    let controller = HitsObservableController<String>()
+
+    XCTAssertEqual(controller.hits.count, 0)
+    XCTAssertNil(controller.hitsSource)
+  }
+
+  func testReloadWithNoHitsSource() {
+    let controller = HitsObservableController<String>()
+
+    let expectation = self.expectation(description: "hits remain empty")
+
+    controller.reload()
+
+    // Wait for async dispatch to complete
+    DispatchQueue.main.asyncAfter(deadline: .now() + 0.1) {
+      XCTAssertEqual(controller.hits.count, 0)
+      expectation.fulfill()
+    }
+
+    waitForExpectations(timeout: 1.0)
+  }
+
+  func testReloadWithEmptyHitsSource() {
+    let controller = HitsObservableController<String>()
+    let interactor = HitsInteractor<String>(infiniteScrolling: .off, showItemsOnEmptyQuery: true)
+
+    controller.hitsSource = interactor
+
+    let expectation = self.expectation(description: "hits updated to empty")
+
+    controller.reload()
+
+    // Wait for async dispatch to complete
+    DispatchQueue.main.asyncAfter(deadline: .now() + 0.1) {
+      XCTAssertEqual(controller.hits.count, 0)
+      expectation.fulfill()
+    }
+
+    waitForExpectations(timeout: 1.0)
+  }
+
+  func testScrollToTop() {
+    let controller = HitsObservableController<String>()
+    let initialScrollID = controller.scrollID
+
+    controller.scrollToTop()
+
+    XCTAssertNotEqual(controller.scrollID, initialScrollID)
+  }
+
+  // MARK: - Thread Safety Tests
+
+  func testReloadIsAsyncAndMainThread() {
+    let controller = HitsObservableController<String>()
+    let interactor = HitsInteractor<String>(infiniteScrolling: .off, showItemsOnEmptyQuery: true)
+
+    controller.hitsSource = interactor
+
+    let expectation = self.expectation(description: "reload completes on main thread")
+
+    // Call reload from a background thread
+    DispatchQueue.global(qos: .background).async {
+      controller.reload()
+
+      // Wait for main thread update
+      DispatchQueue.main.asyncAfter(deadline: .now() + 0.1) {
+        // Verify reload was dispatched to main thread (test passes if no crash)
+        XCTAssertTrue(Thread.isMainThread)
+        expectation.fulfill()
+      }
+    }
+
+    waitForExpectations(timeout: 1.0)
+  }
+
+  // MARK: - Concurrency Tests
+
+  func testConcurrentReloadAndAccessDoesNotCrash() {
+    let controller = HitsObservableController<String>()
+    let interactor = HitsInteractor<String>(infiniteScrolling: .off, showItemsOnEmptyQuery: true)
+
+    controller.hitsSource = interactor
+
+    let expectation = self.expectation(description: "concurrent operations complete")
+    expectation.expectedFulfillmentCount = 2
+
+    // Simulate concurrent reloads
+    DispatchQueue.global(qos: .background).async {
+      for _ in 0..<10 {
+        controller.reload()
+      }
+      expectation.fulfill()
+    }
+
+    // Concurrently access hits array (simulating ForEach iteration)
+    DispatchQueue.main.async {
+      for _ in 0..<50 {
+        let count = controller.hits.count
+        // Try to access indices - should not crash with bounds checking
+        for index in 0..<count {
+          if index < controller.hits.count {
+            _ = controller.hits[index]
+          }
+        }
+        Thread.sleep(forTimeInterval: 0.001)
+      }
+      expectation.fulfill()
+    }
+
+    waitForExpectations(timeout: 5.0)
+  }
+}
+
+// Note: Full integration tests with SearchResponse are in InstantSearchCoreTests.
+// These tests focus on the SwiftUI-specific threading and bounds checking behavior.