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/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at */
* Makes sure that the nested event loop for NSMenu tracking is situated as low
* on the stack as possible, and that two NSMenu event loops are never nested.
#include "MOZMenuOpeningCoordinator.h"
#include "mozilla/ClearOnShutdown.h"
#include "mozilla/StaticPrefs_widget.h"
#include "nsCocoaFeatures.h"
#include "nsCocoaUtils.h"
#include "nsMenuX.h"
#include "nsObjCExceptions.h"
static BOOL sNeedToUnwindForMenuClosing = NO;
@interface MOZMenuOpeningInfo : NSObject
@property NSInteger handle;
@property(retain) NSMenu* menu;
@property NSPoint position;
@property(retain) NSView* view;
@property(retain) NSAppearance* appearance;
@property BOOL isContextMenu;
@implementation MOZMenuOpeningInfo
@implementation MOZMenuOpeningCoordinator {
// non-nil between asynchronouslyOpenMenu:atScreenPosition:forView: and the
// time at at which it is unqueued in _runMenu.
MOZMenuOpeningInfo* mPendingOpening; // strong
// An incrementing counter
NSInteger mLastHandle;
// YES while _runMenu is on the stack
BOOL mRunMenuIsOnTheStack;
+ (instancetype)sharedInstance {
static MOZMenuOpeningCoordinator* sInstance = nil;
if (!sInstance) {
sInstance = [[MOZMenuOpeningCoordinator alloc] init];
mozilla::RunOnShutdown([&]() {
[sInstance release];
sInstance = nil;
return sInstance;
- (void)dealloc {
MOZ_RELEASE_ASSERT(!mPendingOpening, "should be empty at shutdown");
[super dealloc];
- (NSInteger)asynchronouslyOpenMenu:(NSMenu*)aMenu
asContextMenu:(BOOL)aIsContextMenu {
"A menu is already waiting to open. Before opening the "
"next one, either wait "
"for this one to open or cancel the request.");
NSInteger handle = ++mLastHandle;
MOZMenuOpeningInfo* info = [[MOZMenuOpeningInfo alloc] init];
info.handle = handle; = aMenu;
info.position = aPosition;
info.view = aView;
info.appearance = aAppearance;
info.isContextMenu = aIsContextMenu;
mPendingOpening = [info retain];
[info release];
if (!mRunMenuIsOnTheStack) {
// Call _runMenu from the event loop, so that it doesn't block this call.
[self performSelector:@selector(_runMenu) withObject:nil afterDelay:0.0];
return handle;
- (void)_runMenu {
mRunMenuIsOnTheStack = YES;
while (mPendingOpening) {
MOZMenuOpeningInfo* info = [mPendingOpening retain];
[mPendingOpening release];
mPendingOpening = nil;
@try {
} @catch (NSException* exception) {
[info release];
// We have exited _openMenu's nested event loop.
MOZMenuOpeningCoordinator.needToUnwindForMenuClosing = NO;
mRunMenuIsOnTheStack = NO;
- (void)cancelAsynchronousOpening:(NSInteger)aHandle {
if (mPendingOpening && mPendingOpening.handle == aHandle) {
[mPendingOpening release];
mPendingOpening = nil;
- (void)_openMenu:(NSMenu*)aMenu
asContextMenu:(BOOL)aIsContextMenu {
// There are multiple ways to display an NSMenu as a context menu.
// 1. We can return the NSMenu from -[ChildView menuForEvent:] and the NSView
// will open it for us.
// 2. We can call +[NSMenu popUpContextMenu:withEvent:forView:] inside a
// mouseDown handler with a real mouse down event.
// 3. We can call +[NSMenu popUpContextMenu:withEvent:forView:] at a later
// time, with a real mouse event that we stored earlier.
// 4. We can call +[NSMenu popUpContextMenu:withEvent:forView:] at any time,
// with a synthetic mouse event that we create just for that purpose.
// 5. We can call -[NSMenu popUpMenuPositioningItem:atLocation:inView:] and
// it just takes a position, not an event.
// 1-4 look the same, 5 looks different: 5 is made for use with NSPopUpButton,
// where the selected item needs to be shown at a specific position. If a tall
// menu is opened with a position close to the bottom edge of the screen, 5
// results in a cropped menu with scroll arrows, even if the entire menu would
// fit on the screen, due to the positioning constraint. 1-2 only work if the
// menu contents are known synchronously during the call to menuForEvent or
// during the mouseDown event handler.
// NativeMenuMac::ShowAsContextMenu can be called at any time. It could be
// called during a menuForEvent call (during a "contextmenu" event handler),
// or during a mouseDown handler, or at a later time. The code below uses
// option 4 as the preferred option for context menus because it's the
// simplest: It works in all scenarios and it doesn't have the drawbacks of
// option 5. For popups that aren't context menus and that should be
// positioned as close as possible to the given screen position, we use
// option 5.
if (aAppearance) {
if (@available(macOS 11.0, *)) {
// By default, NSMenu inherits its appearance from the opening NSEvent's
// window. If CSS has overridden it, on Big Sur + we can respect it with
// -[NSMenu setAppearance].
aMenu.appearance = aAppearance;
if (aView) {
NSWindow* window = aView.window;
NSPoint locationInWindow =
nsCocoaUtils::ConvertPointFromScreen(window, aPosition);
if (aIsContextMenu) {
// Create a synthetic event at the right location and open the menu
// [option 4].
NSEvent* event =
[NSEvent mouseEventWithType:NSEventTypeRightMouseDown
[NSMenu popUpContextMenu:aMenu withEvent:event forView:aView];
} else {
// For popups which are not context menus, we open the menu using [option
// 5]. We pass `nil` to indicate that we're positioning the top left
// corner of the menu. This path is used for anchored menupopups, so we
// prefer option 5 over option 4 so that the menu doesn't get flipped if
// space is tight.
NSPoint locationInView = [aView convertPoint:locationInWindow
[aMenu popUpMenuPositioningItem:nil
} else {
// Open the menu using popUpMenuPositioningItem:atLocation:inView: [option
// 5]. This is not preferred, because it positions the menu differently from
// how a native context menu would be positioned; it enforces aPosition for
// the top left corner even if this means that the menu will be displayed in
// a clipped fashion with scroll arrows.
[aMenu popUpMenuPositioningItem:nil atLocation:aPosition inView:nil];
+ (void)setNeedToUnwindForMenuClosing:(BOOL)aValue {
sNeedToUnwindForMenuClosing = aValue;
+ (BOOL)needToUnwindForMenuClosing {
return sNeedToUnwindForMenuClosing;