Opening this issue so that anyone coming in from the community is able to discover this known issue with Xcode 9.
Based on some initial reading, it sounds like this is the result of Apple releasing a brand new editor in Xcode 9, which is able to support newer forms of folding for Swift contexts, but ONLY allows for (un)folding entire classes and methods in C contexts (such as Objective-C).
Opening this issue so that anyone coming in from the community is able to discover this known issue with Xcode 9.
Based on some initial reading, it sounds like this is the result of Apple releasing a brand new editor in Xcode 9, which is able to support newer forms of folding for Swift contexts, but ONLY allows for (un)folding entire classes and methods in C contexts (such as Objective-C).
https://stackoverflow.com/questions/44401963/xcode-9-expand-collapse-braces-brackets-side-bar-missing/45756408
If you don't like this behavior, please file a radar against Apple for the Xcode component.