From 813f9da8ab69f106055dd4a8fead7bc0a21a251b Mon Sep 17 00:00:00 2001
From: Robert Hensing <robert@roberthensing.nl>
Date: Wed, 5 Jan 2022 13:54:34 +0100
Subject: [PATCH] pkgs.path: Avoid copying when used via flake

---
 flake.nix                       |  2 +-
 pkgs/top-level/all-packages.nix |  2 +-
 pkgs/top-level/config.nix       | 14 ++++++++++++++
 3 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/flake.nix b/flake.nix
index 29dffa9fa4e4..c2306768d6fe 100644
--- a/flake.nix
+++ b/flake.nix
@@ -62,7 +62,7 @@
         }).nixos.manual.x86_64-linux;
       };
 
-      legacyPackages = forAllSystems (system: import ./. { inherit system; });
+      legacyPackages = forAllSystems (system: import ./. { inherit system; config.path = self.outPath; });
 
       nixosModules = {
         notDetected = import ./nixos/modules/installer/scan/not-detected.nix;
diff --git a/pkgs/top-level/all-packages.nix b/pkgs/top-level/all-packages.nix
index 12c16ea3a5d0..3896088f7662 100644
--- a/pkgs/top-level/all-packages.nix
+++ b/pkgs/top-level/all-packages.nix
@@ -67,7 +67,7 @@ with pkgs;
   clangStdenvNoLibs = mkStdenvNoLibs clangStdenv;
 
   # For convenience, allow callers to get the path to Nixpkgs.
-  path = ../..;
+  path = config.path;
 
 
   ### Helper functions.
diff --git a/pkgs/top-level/config.nix b/pkgs/top-level/config.nix
index 7a5b4bdd1798..bb4f668d60f1 100644
--- a/pkgs/top-level/config.nix
+++ b/pkgs/top-level/config.nix
@@ -32,6 +32,20 @@ let
       feature = "run <literal>checkPhase</literal> by default";
     };
 
+    path = mkOption {
+      type = types.path;
+      default = ../..;
+      defaultText = lib.literalDocBook "a path expression";
+      internal = true;
+      description = ''
+        A reference to Nixpkgs' own sources.
+
+        This is overridable in order to avoid copying sources unnecessarily,
+        as a path expression that references a store path will not short-circuit
+        to the store path itself, but copy the store path instead.
+      '';
+    };
+
   };
 
 in {