This is to avoid cyclic dependencies since it was previously in a somewhat high-level framework, so everything that framework depended on, could not augment crash reports.
The first time we ask for the shared spell checker it does some setup involving AppKit (creating the shared spelling panel?). While we already ensure that the spell checker is only called from the main queue, it seems this setup code must run on thread 0, which, when we are not in a Cocoa application, is not necessarily the thread used for the main queue.
Previously this was undefined, yet some code could trigger it. E.g. asking for the OS dictionary pop-up with an empty document.
I wasn’t sure if this should actually be allowed but decided that since operator[] returns strings, the “end of buffer” code point is easily defined as an empty string makes the code using this API simpler.
Unfortunately a printf precision specifier (‘%.*s’) can not come with a width specifier so we have to cast to int. The width specifier ‘t’ is used for ptrdiff_t.
The int → NSInteger change fixed a bug with popup menu positioning, but there was no associated warning or error. It's possible there are more such bugs that we haven't found yet!
