feat(gesture): implement DragGesture

Example/Shared/Event/Gesture/DragGestureExample.swift

@@ -0,0 +1,40 @@
+//
+//  DragGestureExample.swift
+//  Shared
+
+#if OPENSWIFTUI
+import OpenSwiftUI
+#else
+import SwiftUI
+#endif
+
+struct DragGestureExample: View {
+    @State private var position: CGSize = .zero
+    @GestureState private var dragOffset: CGSize = .zero
+
+    var drag: some Gesture {
+        DragGesture()
+            .updating($dragOffset) { value, state, _ in
+                state = value.translation
+            }
+            .onEnded { value in
+                position.width += value.translation.width
+                position.height += value.translation.height
+            }
+    }
+
+    var body: some View {
+        Circle()
+            .fill(dragOffset == .zero ? Color.blue : Color.green)
+            .frame(width: 100, height: 100)
+            .offset(
+                x: position.width + dragOffset.width,
+                y: position.height + dragOffset.height
+            )
+            .gesture(drag)
+    }
+}
+
+#Preview {
+    DragGestureExample()
+}

Example/Tests/OpenSwiftUIInteractionTests/Event/Gesture/DragGestureInteractionTests.swift

@@ -0,0 +1,71 @@
+//
+//  DragGestureInteractionTests.swift
+//  OpenSwiftUIInteractionTests
+
+#if OPENSWIFTUI
+import OpenSwiftUI
+#else
+import SwiftUI
+#endif
+import OpenSwiftUITestsSupport
+import SnapshotTesting
+import Testing
+
+@MainActor
+@Suite(.serialized, .tags(.interaction), .snapshots(record: .never, diffTool: diffTool))
+struct DragGestureInteractionTests {
+    private struct ContentView: View {
+        var minimumDistance: Double
+        var onChanged: (DragGesture.Value) -> Void
+        var onEnded: (DragGesture.Value) -> Void
+
+        var body: some View {
+            Color.red
+                .gesture(
+                    DragGesture(minimumDistance: minimumDistance)
+                        .onChanged { onChanged($0) }
+                        .onEnded { onEnded($0) }
+                )
+        }
+    }
+
+    @Test
+    func dragReportsTranslation() async throws {
+        var changedCount = 0
+        var endedValue: DragGesture.Value?
+        let content = ContentView(
+            minimumDistance: 10.0,
+            onChanged: { _ in changedCount += 1 },
+            onEnded: { endedValue = $0 }
+        )
+        try await withInteractionTestHost(of: content) { host in
+            try await host.drag(by: CGSize(width: 60, height: 0))
+            try await host.waitUntil(endedValue != nil)
+            let value = try #require(endedValue)
+            #expect(changedCount > 0)
+            #expect(abs(value.translation.width - 60) < 1)
+            #expect(abs(value.translation.height) < 1)
+            #expect(abs(value.location.x - value.startLocation.x - 60) < 1)
+        }
+    }
+
+    @Test
+    func dragStartsAfterMinimumDistance() async throws {
+        var changedValues: [DragGesture.Value] = []
+        var endedValues: [DragGesture.Value] = []
+        let content = ContentView(
+            minimumDistance: 10.0,
+            onChanged: { changedValues.append($0) },
+            onEnded: { endedValues.append($0) }
+        )
+        try await withInteractionTestHost(of: content) { host in
+            // A drag shorter than the default minimum distance must not start the gesture.
+            try await host.drag(by: CGSize(width: 4, height: 0), duration: 0.1)
+            try await host.drag(by: CGSize(width: 60, height: 0))
+            try await host.waitUntil(!endedValues.isEmpty)
+            #expect(endedValues.count == 1)
+            let firstChange = try #require(changedValues.first)
+            #expect(firstChange.translation.width >= 10)
+        }
+    }
+}

Example/Tests/OpenSwiftUIInteractionTests/InteractionTests/InteractionTestHost.swift

@@ -107,6 +107,22 @@ struct InteractionTestHost {
         #endif
     }
 
+    /// Drags from the center of the hosted view by `translation`, in view coordinates.
+    func drag(by translation: CGSize, duration: TimeInterval = 0.3) async throws {
+        #if os(macOS)
+        let start = try view.windowHitPoint(for: events)
+        // AppKit window coordinates use a bottom-left origin.
+        let end = CGPoint(x: start.x + translation.width, y: start.y - translation.height)
+        try await events.mouseDrag(from: start, to: end, duration: duration)
+        #else
+        try await onMainRunLoop {
+            let start = try view.windowHitPoint(for: events)
+            let end = CGPoint(x: start.x + translation.width, y: start.y + translation.height)
+            try events.fingerDrag(from: start, to: end, duration: duration)
+        }
+        #endif
+    }
+
     func waitUntil(
         _ condition: @autoclosure @escaping () -> Bool,
         timeout: TimeInterval = 3

Example/Tests/README.md

@@ -59,7 +59,8 @@ The default content size is 200×200 points, shared with UI tests through
 `defaultSize` in [Shared/SnapshotTesting.swift](Shared/SnapshotTesting.swift).
 Pass `size` only when a test needs another content size. The hosted view and its
 snapshots use that size on both macOS and iOS, independently of the screen size.
-Call the helper, `tap()`, and `waitUntil(_:timeout:)` with `try await`.
+Call the helper, `tap()`, `drag(by:duration:)`, and `waitUntil(_:timeout:)` with
+`try await`.
 `assertSnapshot(named:)` captures the current hosted view and preserves its
 state for later interactions:
 

Example/Tuist/Package.swift

@@ -35,7 +35,7 @@ var dependencies: [PackageDescription.Package.Dependency] = [
     .package(url: "https://github.com/OpenSwiftUIProject/equatable.git", branch: "main"),
     .package(url: "https://github.com/OpenSwiftUIProject/SymbolLocator.git", from: "0.2.0"),
     .package(url: "https://github.com/OpenSwiftUIProject/swift-snapshot-testing.git", exact: "1.19.3"),
-    .package(url: "https://github.com/OpenSwiftUIProject/Hammer.git", exact: "0.19.2"),
+    .package(url: "https://github.com/OpenSwiftUIProject/Hammer.git", exact: "0.19.3"),
 ]
 
 if openCombineCondition {