[Work In Progress] Backport of the IBSegueAction feature for iOS < 13

IBSegueActionBackport.h

//
//  ⚠️ WORK IN PROGRESS, NOT FUNCTIONAL ⚠️
//  Backport of the IBSegueAction feature for iOS < 13
//  See https://sarunw.com/posts/better-dependency-injection-for-storyboards-in-ios13/ and https://useyourloaf.com/blog/better-storyboards-with-xcode-11/
//

@import Foundation;

BOOL XCDBackportIBSegueAction(void);

IBSegueActionBackport.m

#import "IBSegueActionBackport.h"

@import ObjectiveC;
@import UIKit;

@interface NSObject (XCDBackport)
- (id) xcd_initWithCoder_UIClassSwapper:(NSCoder *)decoder;
- (id) xcd_initWithCoder_UIStoryboardSegueTemplate:(NSCoder *)decoder;
@end

@interface NSCoder (XCDBackport)
- (id) xcd_decodeObjectForKey:(NSString *)key;
@end

@interface NSDictionary (XCDBackport)
- (id) xcd_objectForKey:(NSString *)key;
@end

@interface NSObject (UIStoryboard)
- (id) nibForViewControllerWithIdentifier:(NSString *)identifier;
@end

@interface NSObject (UIStoryboardScene)
@property (readonly) UIViewController *sceneViewController;
@end

@interface NSObject (UIStoryboardSegueTemplate)
@property (readonly) UIViewController *viewController;
@end

@interface NSObject (UIViewController)
@property NSString *storyboardIdentifier;
@end

@interface UIStoryboard (XCDBackport)

- (nullable __kindof UIViewController *) xcd_instantiateInitialViewControllerWithCreator:(UIStoryboardViewControllerCreator)creator;
- (__kindof UIViewController *) xcd_instantiateViewControllerWithIdentifier:(NSString *)identifier creator:(UIStoryboardViewControllerCreator)creator;
- (__kindof UIViewController *) xcd_instantiateViewControllerWithIdentifier:(NSString *)identifier creator:(UIStoryboardViewControllerCreator)creator storyboardSegueTemplate:(id)storyboardSegueTemplate sender:(id)sender;

@end

static id instantiateOrFindDestinationViewControllerWithSenderIMP(id /* UIStoryboardSegueTemplate */ self, SEL _cmd, id sender)
{
    UIViewController *viewController = [self viewController];
    NSString *identifier = [self valueForKey:@"destinationViewControllerIdentifier"];
    return [viewController.storyboard xcd_instantiateViewControllerWithIdentifier:identifier creator:nil storyboardSegueTemplate:self sender:sender];
}

static Class UIStoryboardScene = Nil;

BOOL XCDBackportIBSegueAction(void)
{
    Method instantiateViewControllerWithIdentifier_creator = class_getInstanceMethod(UIStoryboard.class, @selector(xcd_instantiateViewControllerWithIdentifier:creator:));
    if (!class_addMethod(UIStoryboard.class, @selector(instantiateViewControllerWithIdentifier:creator:), method_getImplementation(instantiateViewControllerWithIdentifier_creator), method_getTypeEncoding(instantiateViewControllerWithIdentifier_creator)))
        return NO; // method already exists => running on iOS 13+
    
    Method instantiateInitialViewControllerWithCreator = class_getInstanceMethod(UIStoryboard.class, @selector(xcd_instantiateInitialViewControllerWithCreator:));
    if (!class_addMethod(UIStoryboard.class, @selector(instantiateInitialViewControllerWithCreator:), method_getImplementation(instantiateInitialViewControllerWithCreator), method_getTypeEncoding(instantiateInitialViewControllerWithCreator)))
        return NO; // method already exists => running on iOS 13+
    
    UIStoryboardScene = NSClassFromString([@[ @"UI", @"Storyboard", @"Scene" ] componentsJoinedByString:@""]);
    if (!UIStoryboardScene)
        return NO;
    
    Class UINibDecoder = NSClassFromString([@[ @"UI", @"Nib", @"Decoder" ] componentsJoinedByString:@""]);
    if (!UINibDecoder)
        return NO;
    
    Method decodeObjectForKeyMethod = class_getInstanceMethod(UINibDecoder, @selector(decodeObjectForKey:));
    Method xcd_decodeObjectForKeyMethod = class_getInstanceMethod(NSCoder.class, @selector(xcd_decodeObjectForKey:));
    method_exchangeImplementations(decodeObjectForKeyMethod, xcd_decodeObjectForKeyMethod);

    Class UIClassSwapper = NSClassFromString([@[ @"UI", @"Class", @"Swapper" ] componentsJoinedByString:@""]);
    if (!UIClassSwapper)
        return NO;

    Method initWithCoderUIClassSwapperMethod = class_getInstanceMethod(UIClassSwapper, @selector(initWithCoder:));
    Method xcd_initWithCoderUIClassSwapperMethod = class_getInstanceMethod(NSObject.class, @selector(xcd_initWithCoder_UIClassSwapper:));
    method_exchangeImplementations(initWithCoderUIClassSwapperMethod, xcd_initWithCoderUIClassSwapperMethod);
    
    Class UIStoryboardSegueTemplate = NSClassFromString([@[ @"UI", @"Storyboard", @"Segue", @"Template" ] componentsJoinedByString:@""]);
    Method instantiateOrFindDestinationViewControllerWithSender = class_getInstanceMethod(UIStoryboardSegueTemplate, NSSelectorFromString([@[ @"instantiate", @"Or", @"Find", @"Destination", @"ViewController", @"With", @"Sender", @":" ] componentsJoinedByString:@""]));
    if (!instantiateOrFindDestinationViewControllerWithSender)
        return NO;
    
    Method initWithCoderUIStoryboardSegueTemplateMethod = class_getInstanceMethod(UIStoryboardSegueTemplate, @selector(initWithCoder:));
    Method xcd_initWithCoderUIStoryboardSegueTemplateMethod = class_getInstanceMethod(NSObject.class, @selector(xcd_initWithCoder_UIStoryboardSegueTemplate:));
    method_exchangeImplementations(initWithCoderUIStoryboardSegueTemplateMethod, xcd_initWithCoderUIStoryboardSegueTemplateMethod);
    
    method_setImplementation(instantiateOrFindDestinationViewControllerWithSender, (IMP)instantiateOrFindDestinationViewControllerWithSenderIMP);
    return YES;
}

static NSMutableDictionary *options;

@implementation UIStoryboard (XCDBackport)

- (nullable __kindof UIViewController *) xcd_instantiateInitialViewControllerWithCreator:(UIStoryboardViewControllerCreator)creator
{
    NSString *designatedEntryPointIdentifier = [self valueForKey:@"designatedEntryPointIdentifier"];
    if (designatedEntryPointIdentifier)
        return [self xcd_instantiateViewControllerWithIdentifier:designatedEntryPointIdentifier creator:creator storyboardSegueTemplate:nil sender:nil];
    return nil;
}

- (__kindof UIViewController *) xcd_instantiateViewControllerWithIdentifier:(NSString *)identifier creator:(UIStoryboardViewControllerCreator)creator
{
    return [self xcd_instantiateViewControllerWithIdentifier:identifier creator:creator storyboardSegueTemplate:nil sender:nil];
}

- (__kindof UIViewController *) xcd_instantiateViewControllerWithIdentifier:(NSString *)identifier creator:(UIStoryboardViewControllerCreator)creator storyboardSegueTemplate:(id)storyboardSegueTemplate sender:(id)sender
{
    UINib *nib = [self nibForViewControllerWithIdentifier:identifier];
    if (nib)
    {
        options = [NSMutableDictionary dictionaryWithObject:@{ @"UIStoryboardPlaceholder": self } forKey:UINibExternalObjects];
        if (storyboardSegueTemplate)
            options[@"UINibSourceSegueTemplate"] = storyboardSegueTemplate;
        if (sender)
            options[@"UINibPerformSegueSender"] = sender;
        if (creator)
            options[@"UINibPerformSegueCreator"] = creator;
        id scene = [[UIStoryboardScene alloc] init];
        [nib instantiateWithOwner:scene options:options];
        options = nil;
        UIViewController *sceneViewController = [scene sceneViewController];
        NSAssert(sceneViewController != nil, @"Could not load the scene view controller for identifier '%@'", identifier);
        if (sceneViewController.storyboardIdentifier == nil) {
            sceneViewController.storyboardIdentifier = identifier;
        }
        return sceneViewController;
    }
    else
    {
        NSString *reason = [NSString stringWithFormat:@"Storyboard (%@) doesn't contain a view controller with identifier '%@'", self, identifier];
        @throw [NSException exceptionWithName:NSInvalidArgumentException reason:reason userInfo:nil];
    }
}

@end

@interface XCDStoryboardDecodingContext : NSObject

@property (nonatomic,retain) id /* UIClassSwapper */ classSwapperTemplate;
@property (nonatomic,retain) id /* UIStoryboardSegueTemplate */ sourceSegueTemplate;
@property (nonatomic,retain) UIViewController * parentViewController;
@property (assign,nonatomic) long long childViewControllerIndex;
@property (nonatomic,retain) id sender;
@property (nonatomic,copy) id creator;

@end

@implementation XCDStoryboardDecodingContext
@end

@implementation NSCoder (XCDBackport)

static void const * const XCDStoryboardDecodingContextKey = &XCDStoryboardDecodingContextKey;

- (XCDStoryboardDecodingContext *) xcd_storyboardDecodingContext
{
    return objc_getAssociatedObject(self, XCDStoryboardDecodingContextKey);
}

- (void) xcd_createStoryboardDecodingContextIfNeeded
{
    if (self.xcd_storyboardDecodingContext == nil)
        objc_setAssociatedObject(self, XCDStoryboardDecodingContextKey, [XCDStoryboardDecodingContext new], OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

- (id) xcd_decodeObjectForKey:(NSString *)key
{
    if (options && [key isEqualToString:@"UINibConnectionsKey"])
        return [self xcd_decodeObjectsWithSourceSegueTemplate:options[@"UINibSourceSegueTemplate"] creator:options[@"UINibPerformSegueCreator"] sender:options[@"UINibPerformSegueSender"] forKey:key];
    else
        return [self xcd_decodeObjectForKey:key]; // swizzled => calls original implementation
}

- (id) xcd_decodeObjectsWithSourceSegueTemplate:(id)sourceSegueTemplate creator:(UIStoryboardViewControllerCreator)creator sender:(id)sender forKey:(NSString *)key
{
    id currentSourceSegueTemplate = self.xcd_storyboardDecodingContext.sourceSegueTemplate;
    id currentSender = self.xcd_storyboardDecodingContext.sender;
    id currentCreator = self.xcd_storyboardDecodingContext.creator;
    [self xcd_createStoryboardDecodingContextIfNeeded];
    self.xcd_storyboardDecodingContext.sourceSegueTemplate = sourceSegueTemplate;
    self.xcd_storyboardDecodingContext.sender = sender;
    self.xcd_storyboardDecodingContext.creator = creator;
    id result = [self xcd_decodeObjectForKey:key]; // swizzled => calls original implementation
    self.xcd_storyboardDecodingContext.sourceSegueTemplate = currentSourceSegueTemplate;
    self.xcd_storyboardDecodingContext.sender = currentSender;
    self.xcd_storyboardDecodingContext.creator = currentCreator;
    return result;
}

@end

@implementation NSObject (XCDBackport)

id (*performPrepareForChildViewController)(id, SEL, id, id, id) = (id (*)(id, SEL, id, id, id)) objc_msgSend;

static void const * const PrepareForChildViewControllerSelectorNameKey = &PrepareForChildViewControllerSelectorNameKey;

- (id) xcd_initWithCoder_UIClassSwapper:(NSCoder *)decoder
{
    // Note: I had aleady reversed -[UIClassSwapper initWithCoder:] on iOS < 13 which was a very small method, see https://gist.github.com/0xced/45daf79b62ad6a20be1c
    
    // TODO: see actual implementation on iOS 13, the current implementation is not complete
    id sourceSegueTemplate = decoder.xcd_storyboardDecodingContext.sourceSegueTemplate;
    id selectorName = objc_getAssociatedObject(sourceSegueTemplate, PrepareForChildViewControllerSelectorNameKey);
    SEL prepareForChildViewControllerSelector = NSSelectorFromString(selectorName);
    UIViewController *viewController = [sourceSegueTemplate viewController];
    if ([viewController respondsToSelector:prepareForChildViewControllerSelector])
    {
        id sender = decoder.xcd_storyboardDecodingContext.sender;
        id segueIdentifier = [sourceSegueTemplate identifier];
        return performPrepareForChildViewController(viewController, prepareForChildViewControllerSelector, decoder, sender, segueIdentifier);
    }
    
    return [self xcd_initWithCoder_UIClassSwapper:decoder];
}

- (id) xcd_initWithCoder_UIStoryboardSegueTemplate:(NSCoder *)decoder
{
    id storyboardSegueTemplate = [self xcd_initWithCoder_UIStoryboardSegueTemplate:decoder];
    id selectorName = [decoder decodeObjectForKey:@"UICustomPrepareForChildViewControllersSegueName"];
    objc_setAssociatedObject(storyboardSegueTemplate, PrepareForChildViewControllerSelectorNameKey, selectorName, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
    return storyboardSegueTemplate;
}

@end

#warning TODO: swizzle -[UIViewController initWithCoder:] and call [decoder _initializeClassSwapperWithCurrentDecodingViewControllerIfNeeded:self]