Make ClassDescendants behave deterministically

[comex]

Sort descendants by class name. This ensures that generators are run in a deterministic order.

(With this, plus changes to xcodeproj, plus manually calling predictabilize_uuids in my Cakefile, I can get the same project.pbxproj output across multiple runs.)

[ghost]

Hi Igor, how are you?
its possible to add pod files in cakefile?

[igor-makarov]

Thanks for another PR @comex!
Frankly, I have given up on having a deterministic PBX and just opt to .gitignore it altogether. What is your use case for having a deterministic PBX?

Also, predictabilize_uuids has caused collisions for me in the past so I haven't been using it.

Also, what changes to Xcodeproj? Could you elaborate?

[igor-makarov]

@d0bl3c3r0 - you can run pod install in the after_save hook (see here) or just invoke it in the command line after Xcake generation.

[comex]

What is your use case for having a deterministic PBX?

Basically, being able to check in the xcodeproj and avoid confusing people about whether, or how much, the build has changed.

Also, predictabilize_uuids has caused collisions for me in the past so I haven't been using it.

I had sort of the opposite problem: predictabilize_uuids didn't actually make UUIDs predictable. The implementation works by iterating over each object, hashing its properties, and assigning a new UUID based on the hash. But in some cases those properties include UUIDs of other objects. It does need to update those properties to point to the new UUIDs (fixup_uuid_references), but it only does that as a separate step after assigning all the new UUIDs. So at the point it hashes the properties, they still point to the old, random UUIDs…

For now, I hacked around that by changing xcodeproj to exclude the problematic properties from the hash. But of course, excluding properties increases the risk of collisions. Also, while I now get the same pbxproj output if the input is identical, if I make even a small change, it causes a cascade of UUID changes that make the pbxproj file seem completely rewritten. I'd prefer smaller diffs.

So I'm going to investigate a different approach.

[igor-makarov]

@comex And gitignoring the PBX is not an option?
After all, the build system functionality is entirely derived from the Cakefile/Podfile...

[comex]

Nope, for various reasons it's not an option for me.