For those interested, some details and progress report on the merging of FSBV into CFFI.

On Saturday, I was about to commit the latest changes to the fsbv branch of CFFI, and I decided at the last minute to swap the load order of cstruct and cif in cffi-fsbv.asd. Previously, I had cif.lisp loading first, and then cstruct.lisp, but it made more sense to me to put it after, because it has to do with functions, and everything else, including cstruct.lisp, did not. Much to my surprise, I got an error, and I quickly realized why: cif defines a structure that libffi needs, and when it is defined prior to cstruct, it made an ordinary foreign structure, without the *cstruct-hooks* I had made that define a foreign structure with the libffi-type pointers. When it's defined after, it got an error because some of the slots have types, like "unsigned" that are undefined in the FSBV sense (i.e., there's no libffi-type for it).

The immediate bug fix would be to just define the types. Eventually I'll do that. But the real issue is that in that design, every type has to have libffi-type information, even if there's no intent to use that structure in a call by value. In the standalone FSBV, that wasn't an issue, because there were two macros, cffi:defcstruct and fsbv:defcstruct, and presumably no one used the latter unless they were going to pass or receive the foreign structure by value. Now all structures once defined would have the libffi plumbing defined, whether they needed it or not.

So I changed my approach, and in the process simplified the code a lot. Instead of making the necessary libffi-type in the defcstruct expansion, it will be made on demand only, when a foreign struct is used by, e.g. defcfun. This happens recursively, so if one structure uses another, both will be made. Once they structure is made, it is attached to the plist of the symbol for the type, so it need not be recomputed.

I'm now dealing with built-in types and coming up against a problem I've struggled with before (in GSLL and Antik): how to map C types (:short, :int, etc.) into established byte sizes (:uint8, :uint16). The problem is that libffi defines the types by their size, and it's up to the user to figure out how to map the common C types to those sizes; this is a topic in C that has always confused me. I notice that CFFI has a mapping in the code at the end of src/types.lisp, but it's not easily accessible to other code, so I think if I break that out as some kind of table it will be useful to generate the appropriate pointers for libffi. Unless someone has a better way.

Liam