add PointerDeviceKind to ScaleStartDetails (flutter#165096)

Adds the `PointerDeviceKind` of the scale start event to
`ScaleStartDetails`, which is currently missing.

This is a bug according to flutter#115061. Additionally, according to the docs:

>Having both a pan gesture recognizer and a scale gesture recognizer is
redundant; scale is a superset of pan. Just use the scale gesture
recognizer.

See also flutter#135936 for similar issues and the PRs fixing them.

If multiple pointers are contacting the screen at scale start, then the
`PointerDeviceKind` of the first pointer is used. In practice this
should be good enough as I don't know of any UI that expects you to use
two different pointer kinds at the same time. However, if this is an
issue, we could either give a list of pointers with their kinds or a set
of all active `PointerDeviceKind`s. I don't think this is necessary
though.

Closes flutter#115061.

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we expect every widget to implement].
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- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant documentation (doc comments with `///`).
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[test-exempt].
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Fixes] where supported.
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Author: yakagami

packages/flutter/lib/src/gestures/scale.dart

@@ -99,6 +99,7 @@ class ScaleStartDetails {
     Offset? localFocalPoint,
     this.pointerCount = 0,
     this.sourceTimeStamp,
+    this.kind,
   }) : localFocalPoint = localFocalPoint ?? focalPoint;
 
   /// The initial focal point of the pointers in contact with the screen.
@@ -134,6 +135,12 @@ class ScaleStartDetails {
   /// Could be null if triggered from proxied events such as accessibility.
   final Duration? sourceTimeStamp;
 
+  /// The kind of the device that initiated the event.
+  ///
+  /// If multiple pointers are touching the screen, the kind of the pointer
+  /// device that first initiated the event is used.
+  final PointerDeviceKind? kind;
+
   @override
   String toString() =>
       'ScaleStartDetails(focalPoint: $focalPoint, localFocalPoint: $localFocalPoint, pointersCount: $pointerCount)';
@@ -771,6 +778,12 @@ class ScaleGestureRecognizer extends OneSequenceGestureRecognizer {
             localFocalPoint: _localFocalPoint,
             pointerCount: pointerCount,
             sourceTimeStamp: _initialEventTimestamp,
+            kind:
+                _pointerQueue.isNotEmpty
+                    ? getKindForPointer(_pointerQueue.first)
+                    : _pointerPanZooms.isNotEmpty
+                    ? getKindForPointer(_pointerPanZooms.keys.first)
+                    : null,
           ),
         );
       });

packages/flutter/test/gestures/scale_test.dart

@@ -1830,4 +1830,91 @@ void main() {
       tap.dispose();
     },
   );
+
+  testGesture('ScaleStartDetails should contain the correct PointerDeviceKind', (
+    GestureTester tester,
+  ) {
+    final ScaleGestureRecognizer scale = ScaleGestureRecognizer();
+
+    bool didStartScale = false;
+    PointerDeviceKind? updatedKind;
+    scale.onStart = (ScaleStartDetails details) {
+      didStartScale = true;
+      updatedKind = details.kind;
+    };
+    scale.onEnd = (ScaleEndDetails details) {
+      didStartScale = false;
+    };
+
+    // The default kind is touch.
+    // ignore: avoid_redundant_argument_values
+    final TestPointer pointer1 = TestPointer(1, PointerDeviceKind.touch);
+    final PointerDownEvent down = pointer1.down(Offset.zero);
+    scale.addPointer(down);
+    tester.closeArena(1);
+    // One-finger panning
+    tester.route(down);
+    tester.route(pointer1.move(const Offset(20.0, 30.0)));
+    expect(didStartScale, isTrue);
+    expect(updatedKind, PointerDeviceKind.touch);
+    tester.route(pointer1.up());
+    expect(didStartScale, isFalse);
+
+    final TestPointer pointer2 = TestPointer(2, PointerDeviceKind.mouse);
+    final PointerDownEvent down2 = pointer2.down(const Offset(10.0, 20.0));
+    scale.addPointer(down2);
+    tester.closeArena(2);
+    tester.route(down2);
+    tester.route(pointer2.move(const Offset(20.0, 30.0)));
+    expect(didStartScale, isTrue);
+    expect(updatedKind, PointerDeviceKind.mouse);
+    tester.route(pointer2.up());
+    expect(didStartScale, isFalse);
+
+    final TestPointer pointer3 = TestPointer(3, PointerDeviceKind.stylus);
+    final PointerDownEvent down3 = pointer3.down(const Offset(10.0, 20.0));
+    scale.addPointer(down3);
+    tester.closeArena(3);
+    tester.route(down3);
+    tester.route(pointer3.move(const Offset(20.0, 30.0)));
+    expect(didStartScale, isTrue);
+    expect(updatedKind, PointerDeviceKind.stylus);
+    tester.route(pointer3.up());
+    expect(didStartScale, isFalse);
+
+    final TestPointer pointer4 = TestPointer(4, PointerDeviceKind.invertedStylus);
+    final PointerDownEvent down4 = pointer4.down(const Offset(10.0, 20.0));
+    scale.addPointer(down4);
+    tester.closeArena(4);
+    tester.route(down4);
+    tester.route(pointer4.move(const Offset(20.0, 30.0)));
+    expect(didStartScale, isTrue);
+    expect(updatedKind, PointerDeviceKind.invertedStylus);
+    tester.route(pointer4.up());
+    expect(didStartScale, isFalse);
+
+    final TestPointer pointer5 = TestPointer(5, PointerDeviceKind.unknown);
+    final PointerDownEvent down5 = pointer5.down(const Offset(10.0, 20.0));
+    scale.addPointer(down5);
+    tester.closeArena(5);
+    tester.route(down5);
+    tester.route(pointer5.move(const Offset(20.0, 30.0)));
+    expect(didStartScale, isTrue);
+    expect(updatedKind, PointerDeviceKind.unknown);
+    tester.route(pointer5.up());
+    expect(didStartScale, isFalse);
+
+    final TestPointer pointer6 = TestPointer(6, PointerDeviceKind.trackpad);
+    final PointerPanZoomStartEvent down6 = pointer6.panZoomStart(const Offset(10.0, 20.0));
+    scale.addPointerPanZoom(down6);
+    tester.closeArena(6);
+    tester.route(down6);
+    tester.route(pointer6.panZoomUpdate(const Offset(20.0, 30.0)));
+    expect(didStartScale, isTrue);
+    expect(updatedKind, PointerDeviceKind.trackpad);
+    tester.route(pointer6.panZoomEnd());
+    expect(didStartScale, isFalse);
+
+    scale.dispose();
+  });
 }