If you get an [NSProxy doesNotRecognizeSelector:_accessibilityLoadAccessibilityInformation] crash in iOS 12, here's a temporary fix for your tests. Please change the prefix before you use this! MIT licensed.

TestCaseSubclass.m

static void PSPDFFixiOS12AccessibilityTestCrash(void) {
    let accessibilityLoaderClass = NSClassFromString(@"UIAccessibilityInformationLoader");
    let accessibilitySEL = NSSelectorFromString(@"_loadAccessibilityInformationOnMainThread:");
    __block IMP originalIMP = pspdf_swizzleSelectorWithBlock(accessibilityLoaderClass, accessibilitySEL, ^(id _self, BOOL onMainThread) {
        @try {
            ((void (*)(id, SEL, BOOL))originalIMP)(_self, accessibilitySEL, onMainThread);
        } @catch (NSException *exception) {
            NSLog(@"Exception received: %@", exception);
            if ([exception.name isEqualToString:NSInvalidArgumentException] && [exception.reason containsString:@"_accessibilityLoadAccessibilityInformation"]) {
                NSLog(@"Ignoring IOS 12b5 weirdness...");
            } else {
                // Rethrow other things
                @throw exception;
            }
        }
    });
}



// If you don't yet have such swizzling helpers, here's ours:

// Extracted straight from the ObjC Runtime headers:
// https://opensource.apple.com/source/objc4/objc4-493.9/runtime/objc-abi.h
//
// objc_msgSendSuper2() takes the current search class, not its superclass.
OBJC_EXPORT id objc_msgSendSuper2(struct objc_super *super, SEL op, ...)
__OSX_AVAILABLE_STARTING(__MAC_10_5, __IPHONE_2_0);
OBJC_EXPORT void objc_msgSendSuper2_stret(struct objc_super *super, SEL op,...)
__OSX_AVAILABLE_STARTING(__MAC_10_5, __IPHONE_2_0);

// http://defagos.github.io/yet_another_article_about_method_swizzling/
// Returns the original implementation
PSPDF_EXTERN _Nullable IMP pspdf_swizzleSelector(Class clazz, SEL selector, IMP newImplementation) {
    NSCParameterAssert(clazz);
    NSCParameterAssert(selector);
    NSCParameterAssert(newImplementation);

    // If the method does not exist for this class, do nothing.
    const Method method = class_getInstanceMethod(clazz, selector);
    if (!method) {
        PSPDFLogError(@"%@ doesn't exist in %@.", NSStringFromSelector(selector), NSStringFromClass(clazz));
        // Cannot swizzle methods which are not implemented by the class or one of its parents.
        return NULL;
    }

    // Make sure the class implements the method. If this is not the case, inject an implementation, only calling 'super'.
    const char *types = method_getTypeEncoding(method);

    @synchronized(clazz) {
// class_addMethod will simply return NO if the method is already implemented.
#if !defined(__arm64__)
        // Sufficiently large struct
        typedef struct LargeStruct_ { char dummy[16]; } LargeStruct;

        NSUInteger retSize = 0;
        NSGetSizeAndAlignment(types, &retSize, NULL);

        // Large structs on 32-bit architectures
        // TODO: This is incorrect for some structs on some architectures. Needs to be hardcoded, this cannot be safely inferred at runtime.
        // https://twitter.com/gparker/status/1028564412339113984
        if (sizeof(void *) == 4 && types[0] == _C_STRUCT_B && retSize != 1 && retSize != 2 && retSize != 4 && retSize != 8) {
            class_addMethod(clazz, selector, imp_implementationWithBlock(^(__unsafe_unretained id self, va_list argp) {
                struct objc_super super = {self, clazz};
                return ((LargeStruct(*)(struct objc_super *, SEL, va_list))objc_msgSendSuper2_stret)(&super, selector, argp);
            }), types);
        }
        // All other cases
        else {
#endif
            class_addMethod(clazz, selector, imp_implementationWithBlock(^(__unsafe_unretained id self, va_list argp) {
                struct objc_super super = {self, clazz};
                return ((id(*)(struct objc_super *, SEL, va_list))objc_msgSendSuper2)(&super, selector, argp);
            }), types);
#if !defined(__arm64__)
        }
#endif
        // Swizzling
        return class_replaceMethod(clazz, selector, newImplementation, types);
    }
}

PSPDF_EXTERN _Nullable IMP pspdf_swizzleSelectorWithBlock(Class clazz, SEL selector, id newImplementationBlock) {
    const IMP newImplementation = imp_implementationWithBlock(newImplementationBlock);
    return pspdf_swizzleSelector(clazz, selector, newImplementation);
}

Yes, we fixed the bug by fixing our proxy forwarder logic. The 3-step process from respondsToSelector, methodSignature and forwardInvocation needs to be consistent for any call - even unexpected ones. We use a pre-built cache to speed up lookups and didn't consider the case where unexpected calls might be sent - especially for custom Apple-internal object categories that might skip the respondsToSelector part.

@steipete I'm getting this error in a production app using PSPDFKit 7.6.2. Was this fixed on a later release? Thanks.

This has been fixed in PSPDFKit 7.7.2 for iOS.

Here's the detailed changelog: https://pspdfkit.com/changelog/ios/#7.7.2

See: Fixes an issue where iOS 12 could throw an exception inside -[UIAccessibilityInformationLoader _loadAccessibilityInformationOnMainThread:]. (#16489)