القائمة
Pin nixpkgs revisions to build and use older Emacs versions (27, 28, 29) for testing eldev projects. Use when user needs an older Emacs for testing, or mentions emacs27/28/29 and nix.
التثبيت باستخدام Codex أو Claude انسخ هذا Prompt والصقه في Codex أو Claude أو مساعد آخر ليراجع صفحة Skill ويثبّتها لك.
استنادا إلى تصنيف SOC المهني
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Configure and build Elisp projects using Eldev. Manage dependencies from package archives, Git repos, and local sources. Run tests with ERT, byte-compile projects, launch interactive Emacs sessions with project context, and manage loading modes. Use when user mentions eldev, an Eldev file, or an Elisp project with dependencies.
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Ultra-compressed communication mode. Cuts token usage ~75% by speaking like caveman while keeping full technical accuracy. Supports intensity levels: lite, full (default), ultra. Use when user says "caveman mode", "talk like caveman", "use caveman", "less tokens", "be brief", or invokes /caveman. Also auto-triggers when token efficiency is requested.
| name | older-emacs-via-nix |
| description | Pin nixpkgs revisions to build and use older Emacs versions (27, 28, 29) for testing eldev projects. Use when user needs an older Emacs for testing, or mentions emacs27/28/29 and nix. |
The current nixos-unstable channel only ships emacs (the latest, e.g. 30.2) and emacs30. Older majors (emacs28, emacs29) are removed once they fall out of nixpkgs's active set. To get them, pin a revision:
| Want | nixpkgs branch | Version shipped |
|---|---|---|
| Emacs 29 | nixos-24.05 | 29.4 |
| Emacs 28 | nixos-23.11 | 28.2 |
| Emacs 27 | nixos-22.05 | 27.2 |
One-shot build — write a tiny .nix expression to /tmp and nix-build it:
cat > /tmp/emacs29.nix <<'EOF'
let
pkgs = import (fetchTarball {
url = "https://github.com/NixOS/nixpkgs/archive/nixos-24.05.tar.gz";
}) {};
in pkgs.emacs29
EOF
nix-build /tmp/emacs29.nix --no-out-link
nix-build prints the store path (e.g. /nix/store/...-emacs-29.4). The binary is at <store-path>/bin/emacs. Omit --no-out-link to register a GC root.
For a reproducible pin (fetchTarball follows the branch tip, so the hash drifts over time):
let
pkgs = import (fetchTarball {
url = "https://github.com/NixOS/nixpkgs/archive/<commit-sha>.tar.gz";
sha256 = "<nix-prefetch-url-output>";
}) {};
in pkgs.emacs29
Get the sha256:
nix-prefetch-url --unpack https://github.com/NixOS/nixpkgs/archive/<commit-sha>.tar.gz
Headless variants (substitute the attribute name, faster builds for --batch):
pkgs.emacs29-nox — no X/GTKpkgs.emacs29-gtk3 / pkgs.emacs29-pgtkAdd to shell.nix for multiple Emacs versions together:
{ pkgs ? import <nixpkgs> {} }:
let
oldPkgs = import (fetchTarball {
url = "https://github.com/NixOS/nixpkgs/archive/nixos-24.05.tar.gz";
}) {};
in
pkgs.mkShell {
buildInputs = [ pkgs.emacs oldPkgs.emacs29 /* eldev, etc. */ ];
}
Both land on PATH; disambiguate by full path or by EMACS= (see the eldev skill's Targeting a specific Emacs binary section).