Propagating local variables?

["John Wiegley" <johnw@gnu.org>]

I'd like to create a module, propagate.el, which defines a new class of buffer
local variables: buffer local variables that propagate to any buffers or
processes (in the case of exec-path and process-environment) created on behalf
of the parent.

For example, in certain language modes I have `exec-path' customized to pick
up specific versions of the compiler and debugger. If I run M-x gdb, I'd like
the debugger used to be the one associated with _that_ buffer -- without
making that debugger global to all other buffers (or even available at all).

Right now this idea lies at the heart of Shea Levy's nix-buffer package,
allowing you to have the equivalent of a "nix-shell" within Emacs, so that a
given buffer (and its related child buffers and processes) all see a
consistent set of dependencies as defined by some dir-locals.nix file.

A next step for this project is to abstract out the concept of "propagating
locals" to its own module. However, some of the aspects of implementing it
have proven very hacky, so I'm wondering if we need more low-level support for
this idea. For example, at the moment we do it with advice around
generate-new-buffer. What would be better is to have a general hook for
altering what happens when new buffers and processes are created, something
that could "provide an environment" upon creation of these.

All thoughts welcome,
-- 
John Wiegley                  GPG fingerprint = 4710 CF98 AF9B 327B B80F
http://newartisans.com                          60E1 46C4 BD1A 7AC1 4BA2