Hi there! JetBrains has faced with a bug on Apple M2 MacBooks when tapping (_not_ pressing) with two fingers on a trackpad generates wrong mouse modifiers (which are returned by [MouseEvent.getModifiersEx](https://docs.oracle.com/en/java/javase/17/docs/api/java.desktop/java/awt/event/InputEvent.html#getModifiersEx())).
As far as I see, OpenJDK bug tracker still doesn't contain such a bug and I don't have rights to create a new one, so the PR doesn't refer any id. Here is the bug link from the JetBrains own tracker: [JBR-4765](https://youtrack.jetbrains.com/issue/JBR-4765/Cannot-invoke-context-menu-by-two-fingers-tapping-on-MacBook-with-M2-chip). The bug is 100% reproducible on M2 MacBooks (at least under macOS 12.5). It's also reproducible on M1 MacBooks, but much more rarely (about 10-15% of reproducibility). ## Steps to reproduce 1. Enable `System Preferences` -> `Trackpad` -> `Tap to click` 2. Tap with two fingers in the following app: import javax.swing.*; import java.awt.event.MouseAdapter; import java.awt.event.MouseEvent; class MouseWindow { final JFrame frame; MouseWindow() { frame = new JFrame(); frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE); frame.setTitle("Mouse window"); frame.addMouseListener(new MouseAdapter() { @Override public void mousePressed(MouseEvent e) { System.out.println(e); } }); frame.pack(); frame.setSize(300, 300); frame.setVisible(true); } public static void main(String[] args) { SwingUtilities.invokeLater(MouseWindow::new); } } ### Expected Printed mouse event has `modifiersEx` is `4096` (which is `InputEvent.BUTTON3_DOWN_MASK`) ### Actual Printed mouse event has `modifiersEx` is `4352` (which is `InputEvent.BUTTON3_DOWN_MASK | InputEvent.META_DOWN_MASK`) ## Evaluation The following happens when a native mouse event reaches Java: 1. `NSEvent.nsToJavaModifiers(0)` called inside [CPlatformResponder.handleMouseEvent():81](https://github.com/openjdk/jdk/blob/5ae6bc23e857535532b59aae674e2b917bbf7284/src/java.desktop/macosx/classes/sun/lwawt/macosx/CPlatformResponder.java#L81) returns `0`. Earlier it always returned `4096` (`InputEvent.BUTTON3_DOWN_MASK`) but not in the cases of M2 tapping. For a trackpad press (not a tap) it still returns `4096`; 2. So, the `0` modifier comes into MouseEvent constructor which then [goes into MouseEvent.setOldModifiers()](https://github.com/openjdk/jdk/blob/5ae6bc23e857535532b59aae674e2b917bbf7284/src/java.desktop/share/classes/java/awt/event/MouseEvent.java#L800) which [initializes the field MouseEvent.modifiers to the value 4](https://github.com/openjdk/jdk/blob/5ae6bc23e857535532b59aae674e2b917bbf7284/src/java.desktop/share/classes/java/awt/event/MouseEvent.java#L1159) (it's `InputEvent.BUTTON3_MASK`); 3. Next, this constructed `MouseEvent` object is pushed into EDT queue. 4. Next, when a EDT thread pulls the event from the queue and starts to process it, it goes into `java.awt.LightweightDispatcher.retargetMouseEvent` and [creates a new MouseEvent based on the pulled one](https://github.com/openjdk/jdk/blob/5ae6bc23e857535532b59aae674e2b917bbf7284/src/java.desktop/share/classes/java/awt/Container.java#L4920) with the new value of the modifiers == `getModifiersEx() | getModifiers()`. From the p.2 we know, that `MouseEvent.modifiers` of the pulled event is `4`, so `getModifiersEx() | getModifiers()` is evaluated to `4`. 5. Next, the constructor of the new MouseEvent [goes into setNewModifiers()](https://github.com/openjdk/jdk/blob/5ae6bc23e857535532b59aae674e2b917bbf7284/src/java.desktop/share/classes/java/awt/event/MouseEvent.java#L795) (instead of `setOldModifiers` as in p.2) and initializes its own field modifiers to the value `4356` (`InputEvent.BUTTON3_MASK | InputEvent.BUTTON3_DOWN_MASK | InputEvent.META_DOWN_MASK`, see [setNewModifiers():1099](https://github.com/openjdk/jdk/blob/5ae6bc23e857535532b59aae674e2b917bbf7284/src/java.desktop/share/classes/java/awt/event/MouseEvent.java#L1099), [setNewModifiers():1129](https://github.com/openjdk/jdk/blob/5ae6bc23e857535532b59aae674e2b917bbf7284/src/java.desktop/share/classes/java/awt/event/MouseEvent.java#L1129)). 6. Thus, an app receives the instance of MouseEvent with `getModifiers()` == `4` and `getModifiersEx()` == `4352` so it thinks there is a `Command` keystroke. ## Fixing Let's set manually inside `CPlatformResponder.handleMouseEvent` a mouse modifier which corresponds to the pressed button. ## What about a regression test I've failed to write a regression test using Robot because it somehow forces the correct mouse modifiers (`NSEvent.nsToJavaModifiers()` correctly returns `InputEvent.BUTTON3_DOWN_MASK`), so I wrote a test that directly invokes `CPlatformResponder.handleMouseEvent` via reflection. ------------- Commit messages: - 8294426: Two fingers tap generates wrong mouse modifiers on M2 MacBooks Changes: https://git.openjdk.org/jdk/pull/10429/files Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10429&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8294426 Stats: 365 lines in 2 files changed: 365 ins; 0 del; 0 mod Patch: https://git.openjdk.org/jdk/pull/10429.diff Fetch: git fetch https://git.openjdk.org/jdk pull/10429/head:pull/10429 PR: https://git.openjdk.org/jdk/pull/10429
