Fix crash on startup when the X11 server supports XInput < 2.4

[can2049]

Summary

• Fix crash on startup when the X11 server supports XInput < 2.4 (e.g. XInput 2.3)
• Gesture event mask bits (pinch begin/update/end) are now only requested when the server advertises XInput >= 2.4
• Zed previously failed to open any window on affected systems, printing Zed failed to open a window: X11 XiSelectEvents failed

Self-Review Checklist:

• I've reviewed my own diff for quality, security, and reliability
• Unsafe blocks (if any) have justifying comments
• The content is consistent with the UI/UX checklist
• Tests cover the new/changed behavior
• Performance impact has been considered and is acceptable

Problem

On X11 systems where the XInput extension version is older than 2.4, Zed crashes immediately on startup with:

Zed failed to open a window: X11 XiSelectEvents failed.

Caused by:
    X11 error X11Error { error_kind: Value, error_code: 2, sequence: 277,
    bad_value: 27, minor_opcode: 46, major_opcode: 131,
    extension_name: Some("XInputExtension"),
    request_name: Some("XISelectEvents") }

This makes Zed completely unusable on any X11 display server that only supports XInput 2.3 or earlier, which includes many current Ubuntu 20.04/22.04 systems, remote X11 sessions, and VNC/Xvfb setups.

Root cause

During window creation, X11WindowState::new calls XISelectEvents with an event mask that unconditionally includes gesture event bits (GESTURE_PINCH_BEGIN, GESTURE_PINCH_UPDATE, GESTURE_PINCH_END). These gesture events were introduced in XInput 2.4.

When the X server only supports XInput 2.3 (or older), it does not recognize these mask bits and rejects the entire XISelectEvents request with a BadValue error. This is fatal because the error is propagated up and prevents the window from being created.

A comment in the original code stated:

If the server only supports an older version, gesture events simply won't be delivered.

This is incorrect. The X11 protocol does not silently ignore unknown mask bits in XISelectEvents — it rejects the whole request.

How XInput version negotiation works

The client calls XIQueryVersion(2, 4) to announce the highest version it supports. The server responds with the highest version it supports (e.g. 2.3). The client is then responsible for not using features beyond the negotiated version. The existing code ignored the server's response and used 2.4 features unconditionally.

Fix

Approach

Check the XInput version returned by the server. Only include gesture event mask bits in XISelectEvents when the negotiated version is >= 2.4. On older servers, basic input events (motion, button press/release, enter, leave) still work normally — only touchpad pinch gestures are unavailable.

Changed files

crates/gpui_linux/src/linux/x11/client.rs

1. Added supports_xinput_gestures: bool field to X11ClientState.
2. After the existing xinput_xi_query_version(2, 4) call, compute whether the server version is >= 2.4:

   let supports_xinput_gestures = xinput_version.major_version > 2
       || (xinput_version.major_version == 2 && xinput_version.minor_version >= 4);

3. Added an info! log line reporting the detected XInput version and gesture support status.
4. Pass supports_xinput_gestures through open_window into X11Window::new.

crates/gpui_linux/src/linux/x11/window.rs

1. Added supports_xinput_gestures: bool parameter to both X11Window::new and X11WindowState::new.
2. The XISelectEvents call now builds the event mask conditionally:
   • Always includes: MOTION, BUTTON_PRESS, BUTTON_RELEASE, ENTER, LEAVE
   • Only when supports_xinput_gestures is true: GESTURE_PINCH_BEGIN, GESTURE_PINCH_UPDATE, GESTURE_PINCH_END

What is NOT changed

• The gesture event handlers in client.rs (XinputGesturePinchBegin, XinputGesturePinchUpdate, XinputGesturePinchEnd) are left as-is. They simply won't be triggered on servers without gesture support, since the events are never registered.
• No behavioral change on systems with XInput >= 2.4 — gesture events continue to work exactly as before.

Testing

Test	Before fix	After fix
./target/release/zed . on XInput 2.3	Immediate crash (exit code 1)	Window opens successfully (runs until killed)
XInput version detection	Version queried but response ignored	Version checked and logged

Verified on an X11 system with XInput 2.3 (X.Org 1.20.13, Ubuntu 20.04).

Test plan

• Build succeeds (cargo build --release)
• Zed launches and opens a window on XInput 2.3 system
• No regression on the basic input event path (motion, clicks, enter/leave still registered)
• Verify gesture pinch events still work on a system with XInput >= 2.4

Release Notes:

• Fixed Zed failing to start on X11 systems with XInput version older than 2.4, which includes many Linux distributions and remote desktop setups.

[Veykril]

Thanks!