Re: Dynamic loading progress

[Paul Eggert <eggert@cs.ucla.edu>]

To help make progress on the plugin compatibility issue I installed commit 
65563fd7714271582d5146c09202c0f7a0631fe5 in the master.  A plugin should do this:

#define DEFINE_NONNIL_Q_SYMBOL_MACROS false

before including globals.h either directly or indirectly.  This #define could be 
part of any new emacs.h.

We're not out of the woods yet, I'm afraid.  For example, suppose a new version 
of Emacs adds a new kind of function, and that the implementation of functionp 
changes.  And suppose a plugin is compiled with the old version of Emacs and 
uses the FUNCTIONP macro.  Since FUNCTIONP's expansion calls functionp and 
functionp is an extern inline function, the plugin may use the old version of 
functionp or it may use the new one -- the C standard allows either behavior. 
Either way, the plugin may misbehave.

This sort of thing suggests that it may be difficult to guarantee upward 
compatibility of plugins from one version of Emacs to the next.  And perhaps we 
shouldn't even try.

This raises another question: what exactly should go into emacs.h?  The more we 
put into emacs.h, the more likely plugin compatibility won't survive the 
transition from one version of Emacs to the next.