1 files changed, 36 insertions, 0 deletions
diff --git a/tools/nixery/prepare-image/load-pkgs.nix b/tools/nixery/prepare-image/load-pkgs.nix
new file mode 100644
index 000000000000..7f8ab5479d7e
--- /dev/null
+++ b/tools/nixery/prepare-image/load-pkgs.nix
@@ -0,0 +1,36 @@
+# Copyright 2022 The TVL Contributors
+# SPDX-License-Identifier: Apache-2.0
+
+# Load a Nix package set from one of the supported source types
+# (nixpkgs, git, path).
+{ srcType, srcArgs, importArgs ? { } }:
+
+with builtins;
+let
+  # If a nixpkgs channel is requested, it is retrieved from Github (as
+  # a tarball) and imported.
+  fetchImportChannel = channel:
+    let
+      url =
+        "https://github.com/NixOS/nixpkgs/archive/${channel}.tar.gz";
+    in
+    import (fetchTarball url) importArgs;
+
+  # If a git repository is requested, it is retrieved via
+  # builtins.fetchGit which defaults to the git configuration of the
+  # outside environment. This means that user-configured SSH
+  # credentials etc. are going to work as expected.
+  fetchImportGit = spec: import (fetchGit spec) importArgs;
+
+  # No special handling is used for paths, so users are expected to pass one
+  # that will work natively with Nix.
+  importPath = path: import (toPath path) importArgs;
+in
+if srcType == "nixpkgs" then
+  fetchImportChannel srcArgs
+else if srcType == "git" then
+  fetchImportGit (fromJSON srcArgs)
+else if srcType == "path" then
+  importPath srcArgs
+else
+  throw ("Invalid package set source specification: ${srcType} (${srcArgs})")