Propagating local variables?

[John Wiegley]

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,

[Roland Winkler]

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[Stefan Monnier]

Post by Roland Winkler
I have always considered this a hack. But I could not think of a better
solution. Suggestions are welcome.

I think most other "multi-buffer" packages tend to treat one of their
buffers as a kind of "master" and have all others point to it, so they
can lookup shared local variables via something like
(buffer-local-value my-parent-buffer 'varname).


Stefan

[John Wiegley]

SM> I think most other "multi-buffer" packages tend to treat one of their
SM> buffers as a kind of "master" and have all others point to it, so they can
SM> lookup shared local variables via something like (buffer-local-value
SM> my-parent-buffer 'varname).

If you're the author of all the code that relates to that buffer, sure. But I
can't expect shell.el to reference the buffer-local `process-environment' of
my Coq buffer in order to setup the right PATH for that project-specific
sub-shell.