Re: Emacs contributions, C and Lisp

[Jacob Bachmeyer <jcb62281@gmail.com>]

Richard Stallman wrote:
> [[[ To any NSA and FBI agents reading my email: please consider    ]]]
> [[[ whether defending the US Constitution against all enemies,     ]]]
> [[[ foreign or domestic, requires you to follow Snowden's example. ]]]
>
>   > This illuminates the central question at hand:  if an Emacs plugin is 
>   > GPL, and provides access to internals of GCC, which is also GPL, can 
>   > nonfree software use that Emacs plugin?
>
> "Use" is too broad a word; such a broad question has no answer.
>   
> Nonfree software can't be _combined_ with GPL'd code, which includes
> that plug-in (what the plug-in _does_ is beside the point).  If a
> program A "uses" a program B, does this mean the two are combined?
> That depends on details (and there may be a gray area; also, we can't
> be sure where courts will say the border is).  

Plugins of this type are DSOs, so "use" means "dynamically link at 
runtime" and "call functions the plugin implements".  I think that the 
GPL FAQ answers this in 
<URL:http://www.gnu.org/licenses/gpl-faq.html#GPLPluginsInNF>.  Since 
using a GPL plugin in a non-free program requires additional permission 
on the part of the plugin, which GCC would _not_ provide, non-free 
software could not dynamically link the plugin.

> What I am pretty sure of is that if the plug-in generates the AST as
> text, a GPL-covered program could write it into a file, and some
> separate proprietary program could read the file, and this would not
> be considered combining the two programs.  It would be lawful, and
> could be quite harmful.
>   

This is why I am proposing a two-faced (one face for GCC, one for Emacs) 
link plugin that gets the AST from GCC via some (currently unspecified, 
but using ptrace(2) is not out of the question) host-platform-specific 
binary means and presents it to Emacs as some kind of in-memory data 
structure.  Although, after it was pointed out, I now see the possible 
problem that someone could write Emacs Lisp code to dump that structure 
as text.

But all this is sounding more and more like we could not stop someone 
who really wanted the AST in any case.  If a developer of non-free 
software could use any facility we develop to import an AST from GCC 
into Emacs, what stops that same developer from simply writing their own 
AST export plugin for GCC and making just the AST dumper GPL?

> This is why there is danger in generating the AST as text.

This is why I do not propose exporting a text AST.