gecko-dev/widget/cocoa/MOZMenuOpeningCoordinator.mm

/* -*- 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 http://mozilla.org/MPL/2.0/. */

/*
 * 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;
@end

@implementation MOZMenuOpeningInfo
@end

@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
                   atScreenPosition:(NSPoint)aPosition
                            forView:(NSView*)aView
                     withAppearance:(NSAppearance*)aAppearance
                      asContextMenu:(BOOL)aIsContextMenu {
  MOZ_RELEASE_ASSERT(!mPendingOpening,
                     "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;
  info.menu = 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 {
  MOZ_RELEASE_ASSERT(!mRunMenuIsOnTheStack);

  mRunMenuIsOnTheStack = YES;

  while (mPendingOpening) {
    MOZMenuOpeningInfo* info = [mPendingOpening retain];
    [mPendingOpening release];
    mPendingOpening = nil;

    @try {
      [self _openMenu:info.menu
          atScreenPosition:info.position
                   forView:info.view
            withAppearance:info.appearance
             asContextMenu:info.isContextMenu];
    } @catch (NSException* exception) {
      nsObjCExceptionLog(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) {
    [NSObject cancelPreviousPerformRequestsWithTarget:self
                                             selector:@selector(_runMenu)
                                               object:nil];
    [mPendingOpening release];
    mPendingOpening = nil;
  }
}

- (void)_openMenu:(NSMenu*)aMenu
    atScreenPosition:(NSPoint)aPosition
             forView:(NSView*)aView
      withAppearance:(NSAppearance*)aAppearance
       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
                             location:locationInWindow
                        modifierFlags:0
                            timestamp:NSProcessInfo.processInfo.systemUptime
                         windowNumber:window.windowNumber
                              context:nil
                          eventNumber:0
                           clickCount:1
                             pressure:0.0f];
      [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
                                          fromView:nil];
      [aMenu popUpMenuPositioningItem:nil
                           atLocation:locationInView
                               inView:aView];
    }
  } 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;
}

@end