Thank you so much for trying to help me with this baffling problem. Searching the XCode documentation and IDE I don't see where I can display the preprocessor's output. Where is it?

Preprocessing the file reports the errors. XCode doesn't even get to the build phase before it encounters the fatal errors. Yes, I have been programming with C for a while - on the Mac since about 1998. On, a somewhat positive note, I sent an example of a project that won't build to DTS. They have it and it won't build for them either. Engineers at Apple are trying to see what XCode is doing to me.

I misunderstood what you said. I preprocessed some .m and .c files and I don't see any errors in them but they still won't build.

I preprocessed some simple .c and .m files with a few functions and headers. The preprocessed files have the function declarations, enums, etc. in them but no errors are reported. Then they won't build with the same weird errors. This looks like a problem with the build system in XCode.

This morning my playgrounds started to work again. Oi vey indeed...

So ClassName would be AppTransaction? XCode won't build this: "Use of undeclared identifier 'AppTransaction'"

Example of the code you use to call AppTransaction?

I think the .plist has to have some references to the help Book.

I'm using XCode 26.2 and I have the same problem as you. Is this apparently HORRIBLE bug documented anywhere?