PointerConstraint: fix assertion failure

The assertion in PointerConstraint.confine() can currently still be
triggered if the input region of a surface is changed and the pointer is
moved outside of the new intersection of input region and constraint
region before PointerConstraint.updateState() is called.

This can happen, for example, when a client is made non-fullscreen at
the same time as the pointer is moved across the boundary of the new,
post-fullscreen, input region. If the pointer crosses the boundary
before the transaction completes and updateState() is called, the
assertion in PointerConstraint.confine() will fail.

To fix this, listen for the surface commit event rather than the
set_region event to handle possible deactivation on region changes.

 river/PointerConstraint.zig | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/river/PointerConstraint.zig b/river/PointerConstraint.zig
index b35b29f..deadc2d 100644
--- a/river/PointerConstraint.zig
+++ b/river/PointerConstraint.zig
@@ -42,7 +42,7 @@ state: union(enum) {
 } = .inactive,
 
 destroy: wl.Listener(*wlr.PointerConstraintV1) = wl.Listener(*wlr.PointerConstraintV1).init(handleDestroy),
-set_region: wl.Listener(void) = wl.Listener(void).init(handleSetRegion),
+commit: wl.Listener(*wlr.Surface) = wl.Listener(*wlr.Surface).init(handleCommit),
 
 node_destroy: wl.Listener(void) = wl.Listener(void).init(handleNodeDestroy),
 
@@ -58,7 +58,7 @@ pub fn create(wlr_constraint: *wlr.PointerConstraintV1) error{OutOfMemory}!void
     wlr_constraint.data = @intFromPtr(constraint);
 
     wlr_constraint.events.destroy.add(&constraint.destroy);
-    wlr_constraint.events.set_region.add(&constraint.set_region);
+    wlr_constraint.surface.events.commit.add(&constraint.commit);
 
     if (seat.wlr_seat.keyboard_state.focused_surface) |surface| {
         if (surface == wlr_constraint.surface) {
@@ -201,7 +201,7 @@ fn handleDestroy(listener: *wl.Listener(*wlr.PointerConstraintV1), _: *wlr.Point
     }
 
     constraint.destroy.link.remove();
-    constraint.set_region.link.remove();
+    constraint.commit.link.remove();
 
     if (seat.cursor.constraint == constraint) {
         seat.cursor.constraint = null;
@@ -210,8 +210,11 @@ fn handleDestroy(listener: *wl.Listener(*wlr.PointerConstraintV1), _: *wlr.Point
     util.gpa.destroy(constraint);
 }
 
-fn handleSetRegion(listener: *wl.Listener(void)) void {
-    const constraint: *PointerConstraint = @fieldParentPtr("set_region", listener);
+// It is necessary to listen for the commit event rather than the set_region
+// event as the latter is not triggered by wlroots when the input region of
+// the surface changes.
+fn handleCommit(listener: *wl.Listener(*wlr.Surface), _: *wlr.Surface) void {
+    const constraint: *PointerConstraint = @fieldParentPtr("commit", listener);
     const seat: *Seat = @ptrFromInt(constraint.wlr_constraint.seat.data);
 
     switch (constraint.state) {
@@ -219,7 +222,7 @@ fn handleSetRegion(listener: *wl.Listener(void)) void {
             const sx: i32 = @intFromFloat(state.sx);
             const sy: i32 = @intFromFloat(state.sy);
             if (!constraint.wlr_constraint.region.containsPoint(sx, sy, null)) {
-                log.info("deactivating pointer constraint, region change left pointer outside constraint", .{});
+                log.info("deactivating pointer constraint, (input) region change left pointer outside constraint", .{});
                 constraint.deactivate();
             }
         },