[Nix-dev] Announcing nix-buffer, nix-shell for emacs

Wed Sep 7 12:04:05 CEST 2016

That part might, but you need to regenerate the library path
regardless.

zimbatm <zimbatm at zimbatm.com> writes:

> Interesting. Would it also work if you set "coq-prog-name" to "coqtop" and
> let emacs resolve the program name from the PATH?
>
> On Tue, 6 Sep 2016 at 10:39 Shea Levy <shea at shealevy.com> wrote:
>
>> Hmm, I think we need more than just environment variables. See for
>> example my recent commit[1] to nixpkgs, where in addition to setting up
>> process-environment and exec-path I also set, when appropriate, several
>> proofgeneral variables like coq-prog-name and even call some
>> proofgeneral functions.
>>
>> ~Shea
>>
>> [1]:
>> https://github.com/NixOS/nixpkgs/commit/b04cdae902398aa76fb81a0470e18fd527c6ba3d
>> zimbatm <zimbatm at zimbatm.com> writes:
>>
>> > Hi Shea,
>> >
>> > did you look at direnv[1] yet? I have a feeling that it would mix with
>> > emacs pretty well and implement all that you need in a more generic way
>> > (which is a pro and con).
>> >
>> > Essentially what I do in my projects is use the following .envrc:
>> > ```bash
>> > use nix
>> > ```
>> > The `use nix` directive calls nix-shell under the hood so then the usual
>> > default.nix and shell.nix are loaded.
>> >
>> > In emacs the plugin would need to call `direnv export json` on
>> enter/leave
>> > of a context. This gives you a diff of environment variables to apply.
>> > There is a bit more complexity when implementing the security framework
>> but
>> > that's about it.
>> >
>> > I'm just curious if you thought of that approach, keep up the good work!
>> >
>> > Cheers,
>> > z
>> >
>> > [1]: http://direnv.net/
>> >
>> > On Mon, 5 Sep 2016 at 17:11 Shea Levy <shea at shealevy.com> wrote:
>> >
>> >> Sure! In my .emacs, I have:
>> >>
>> >> > (defun nix-buffer-find-file-hook ()
>> >> >   (when (not (file-remote-p (buffer-file-name)))
>> >> >     (nix-buffer)))
>> >> > (add-hook 'find-file-hook 'nix-buffer-find-file-hook)
>> >>
>> >> I have coq 8.5pl1 installed in my configuration.nix, but I have a coq
>> >> project that requires 8.4pl6, so I have in that project's root directory
>> >> dir-locals.nix:
>> >>
>> >> > let pkgs = import <nixpkgs> {}; in
>> >> >   pkgs.nixBufferBuilders.withPackages [ pkgs.coq ]
>> >>
>> >> (note that this relies on a recent nixpkgs commit[1]). Then whenever I
>> >> open a .v file in the project, ProofGeneral uses coq 8.4 rather than
>> >> 8.5.
>> >>
>> >> If I wanted, my dir-locals.nix could take a 'root' argument, which would
>> >> point to the file I opened.
>> >>
>> >> ~Shea
>> >>
>> >> [1]:
>> >>
>> https://github.com/NixOS/nixpkgs/commit/05c132486d8cfae600bbfe8c9ac5d799b298afed
>> >>
>> >> Bas van Dijk <v.dijk.bas at gmail.com> writes:
>> >>
>> >> > Hi Shea,
>> >> >
>> >> > As a Nix and Emacs user this looks very interesting. I didn't know
>> about
>> >> > Buffer-Local Variables before.
>> >> >
>> >> > Can you share some applications of nix-buffer / how you are using it?
>> >> >
>> >> > Thanks!
>> >> >
>> >> > Bas
>> >> >
>> >> > On 5 September 2016 at 08:06, Shea Levy <shea at shealevy.com> wrote:
>> >> >
>> >> >> Hi all,
>> >> >>
>> >> >> I've just pushed the initial version of nix-buffer[1], and opened a
>> PR
>> >> >> for adding it to melpa[2]. The description of the 'nix-buffer-enter'
>> >> >> command this library defines:
>> >> >>
>> >> >> > Set up the buffer according to the directory-local nix expression.
>> >> >> >
>> >> >> > Looks for dir-locals.nix upward from the current directory.  If
>> found,
>> >> >> > builds the derivation defined there with the 'root' arg set to the
>> >> >> > current buffer file name or directory and evaluates the resulting
>> >> >> > elisp if safe to do so.
>> >> >> >
>> >> >> > Because in practice dir-locals.nix will always want to do things
>> that
>> >> >> > are unsafe in dir-locals.el (e.g. append to 'exec-path'), we don't
>> >> >> > reuse that mechanism and instead just load the file as elisp.
>> Because
>> >> >> > this allows arbitrary code execution, the first time we're asked to
>> >> >> > load a particular store path we query the user to verify if it's
>> safe
>> >> >> > to load beforehand.
>> >> >> >
>> >> >> > The Lisp code generated by dir-locals.nix should limit itself to
>> >> >> > modifying buffer-local variables, but there is no actual
>> enforcement
>> >> >> > of this.  'setq-local' is your friend.
>> >> >>
>> >> >> It may be useful to advise the 'normal-mode' function to call
>> >> >> 'nix-buffer-enter' beforehand for local files, so that all visited
>> files
>> >> >> have their environments set up before modes are loaded.
>> >> >>
>> >> >> Note that this is my first elisp package, so feedback definitely
>> >> >> welcome!
>> >> >>
>> >> >> In addition to the elisp work mentioned in the TODO[3], it would be
>> >> >> useful to add some functions to nixpkgs to build elisp files,
>> >> >> especially:
>> >> >>
>> >> >> * A function taking a derivation and building an elisp file that
>> sets up
>> >> >>   the buffer environment analogous to the build environment
>> specified by
>> >> >>   that derivation
>> >> >> * A function taking a list of packages and building an elisp file
>> that
>> >> >>   sets up the buffer environment with all of those packages available
>> >> >>   (in PATH, in the emacs load path, etc.).
>> >> >>
>> >> >> Happy hacking!
>> >> >>
>> >> >> ~Shea
>> >> >>
>> >> >> [1]: https://github.com/shlevy/nix-buffer/tree/v1.0
>> >> >> [2]: https://github.com/melpa/melpa/pull/4204
>> >> >> [3]: https://github.com/shlevy/nix-buffer/blob/v1.0/TODO.md
>> >> >>
>> >> >> _______________________________________________
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>> >> >>
>> >> >>
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>> >>
>>
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