I am writing an application that generates .xcodeproj files. It's generated a .pbxproj file, however when opening it in Xcode, I get an error message, "cannot be opened because the project file cannot be parsed." and nothing more.
Is there a reliable application for syntax parsing old-style plists?
If it requires me to use low-level Cocoa APIs, I'm fine with that, but some pointers at least?
You should take a look at Xcodeproj.
It's not a linter, but it may help you to understand why your project isn't being opened correctly.
You have a few options:
This all assumes that your problem is one that could actually be solved by a linter. If your formatting is correct but you're writing values that somehow confuse Xcode then these suggestions may not apply, although I do think reading through the Xcodeproj source would help you.