How did that ever work?

Don't judge the code - this is a tool that was written many many years ago, and it's only a simple thing for personal use. So it was only ever developed to the "it just about works" standard and the project has been copied from computer to computer ever since, receiving the minimum updates to keep it running.

With the beta of 10.14 'Mojave' installed on a mac (which sounds enough like 'Mojito' to raise my pulse) unsurprisingly I started to notice a few things not working as before.

I love finding and fixing problems, so the regular round of fixes with each release of OSX / MacOS  is no hardship. It's particularly fun when you have a "how did that ever work?" moment.

NSArray *pages = [fileManager directoryContentsAtPath:pageLocation];   // NB directoryContentsAtPath: was apparently deprecated in 10.5

if([pages count]==0){return;}

for (c=0;c<[pages count];c++){

// foreach page in the pages directory

thisPage = (NSString *)[pages objectAtIndex:c];

if([[thisPage substringToIndex:1] isEqualToString:@"."]==NO){

// do stuff, ignoring hidden files

[collection addObject:thisPage];

}

}

The resulting list is displayed in a tableview and has always appeared in alphabetical order.

So not only is directoryContentsAtPath: still apparently working after being deprecated such a long time ago, apparently it used to return the directory listing sorted in alphabetical order, and no longer does.

It was easy to add [collection sortUsingSelector:@selector(caseInsensitiveCompare:)];
to restore the list to alphabetical order (collection being an NSMutableArray containing NSStrings) but I'm just surprised  that it wasn't necessary before.

The documentation for directoryContentsAtPath: doesn't mention that the return array is sorted, so it should never have been taken for granted. But hey, if something works the way you want it, you don't always think any further.

To bring this up to scratch, the suggested alternative to directoryContentsAtPath: is 
contentsOfDirectoryAtPath:Error:  so getting rid of that warning is really easy, just declare an NSError object and pass it in. And then report the NSError's 'localizeddescription' if it contains a non-null value. Or simply pass nil as the error: parameter if you feel lazy or don't care about the success of the operation.