1 files changed, 63 insertions, 0 deletions
diff --git a/third_party/nixpkgs/default.nix b/third_party/nixpkgs/default.nix
new file mode 100644
index 000000000000..23f09ff5f716
--- /dev/null
+++ b/third_party/nixpkgs/default.nix
@@ -0,0 +1,63 @@
+# This file imports the pinned nixpkgs sets and applies relevant
+# modifications, such as our overlays.
+#
+# The actual source pinning happens via niv in //third_party/sources
+#
+# Note that the attribute exposed by this (third_party.nixpkgs) is
+# "special" in that the fixpoint used as readTree's config parameter
+# in //default.nix passes this attribute as the `pkgs` argument to all
+# readTree derivations.
+
+{ depot ? { }, externalArgs ? { }, depotOverlays ? true, ... }:
+
+let
+  # import the nixos-unstable package set, or optionally use the
+  # source (e.g. a path) specified by the `nixpkgsBisectPath`
+  # argument. This is intended for use-cases where the depot is
+  # bisected against nixpkgs to find the root cause of an issue in a
+  # channel bump.
+  nixpkgsSrc = externalArgs.nixpkgsBisectPath or depot.third_party.sources.nixpkgs;
+
+  # Stable package set is imported, but not exposed, to overlay
+  # required packages into the unstable set.
+  stableNixpkgs = import depot.third_party.sources.nixpkgs-stable { };
+
+  # Overlay for packages that should come from the stable channel
+  # instead (e.g. because something is broken in unstable).
+  # Use `stableNixpkgs` from above.
+  stableOverlay = _unstableSelf: _unstableSuper: {
+
+    # emacs27 is gone from unstable, but people should upgrade at
+    # their own pace.
+    emacs27 = builtins.trace "emacs27 is deprecated, please migrate to emacs28"
+      stableNixpkgs.emacs27;
+  };
+
+  # Overlay to expose the nixpkgs commits we are using to other Nix code.
+  commitsOverlay = _: _: {
+    nixpkgsCommits = {
+      unstable = depot.third_party.sources.nixpkgs.rev;
+      stable = depot.third_party.sources.nixpkgs-stable.rev;
+    };
+  };
+in
+import nixpkgsSrc {
+  # allow users to inject their config into builds (e.g. to test CA derivations)
+  config =
+    (if externalArgs ? nixpkgsConfig then externalArgs.nixpkgsConfig else { })
+    // {
+      allowUnfree = true;
+      allowBroken = true;
+    };
+
+  overlays = [
+    commitsOverlay
+    stableOverlay
+  ] ++ (if depotOverlays then [
+    depot.third_party.overlays.haskell
+    depot.third_party.overlays.emacs
+    depot.third_party.overlays.tvl
+    depot.third_party.overlays.ecl-static
+    depot.third_party.overlays.dhall
+  ] else [ ]);
+}