Safari 15 Stable Back & Forward buttons in the single-line Unified tab bar

Safari15StableBackFwdButtons.m

#import <Cocoa/Cocoa.h>
#import <objc/runtime.h>

@interface Injector: NSView @end

@implementation Injector

+ (void)load {

    [super load];

    if (![[NSBundle mainBundle].bundleIdentifier containsString:@"SafariTechnologyPreview"])
        return;

    NSLog(@"[SAFARI15FIXER] Swizzling in %@", [NSBundle mainBundle].bundleIdentifier);

    Class toolbarClass = NSClassFromString(@"ToolbarController");

    SEL orgSel = NSSelectorFromString(@"updateBackForwardState");
    Method orgMethod = class_getInstanceMethod(toolbarClass, orgSel);
    Method newMethod = class_getInstanceMethod(self, @selector(toolbar_updateBackForwardState));

    class_addMethod(toolbarClass, @selector(toolbar_updateBackForwardState),
                    method_getImplementation(orgMethod),
                    method_getTypeEncoding(orgMethod));
    class_replaceMethod(toolbarClass, orgSel,
                        method_getImplementation(newMethod),
                        method_getTypeEncoding(newMethod));
}

- (id)delegate { return nil; }
- (id)unifiedTabBar { return nil; }
- (BOOL)isInteractivelyClosingTabs { return YES; }
- (id)backForwardSegmentedControl { return nil; }
- (void)_prepareBackForwardSegmentedControl:(NSSegmentedControl *)segment { }

- (void)toolbar_updateBackForwardState {

    id _self = self;
    id _unifiedTabBar = [_self unifiedTabBar];
    BOOL interactivelyClosing = [_unifiedTabBar isInteractivelyClosingTabs];

    if (interactivelyClosing) return;

    id delegate = [_self delegate];

    NSSegmentedControl *segment = [_self backForwardSegmentedControl];

    if (segment.segmentCount != 2) {
        segment.segmentCount = 2;
    }

    [_self _prepareBackForwardSegmentedControl:segment];
}

@end