proper composable overlay mechanism

wavewave · May 4, 2022 · 388966e · 388966e
1 parent 010656e
commit 388966e
Showing 1 changed file with 9 additions and 3 deletions.
diff --git a/flake.nix b/flake.nix
@@ -34,10 +34,16 @@
         inherit (newHaskellPackages) fficxx fficxx-runtime stdcxx;
       };
 
+      # see these issues and discussions:
+      # - https://github.com/NixOS/nixpkgs/issues/16394
+      # - https://github.com/NixOS/nixpkgs/issues/25887
+      # - https://github.com/NixOS/nixpkgs/issues/26561
+      # - https://discourse.nixos.org/t/nix-haskell-development-2020/6170
       overlay = final: prev: {
-        haskellPackages = prev.haskell.packages.ghc865.override {
-          overrides = finalHaskellOverlay;
-        };
+        haskellPackages = prev.haskellPackages.override (old: {
+          overrides = final.lib.composeExtensions (old.overrides or (_: _: { }))
+            finalHaskellOverlay;
+        });
       };
 
       devShell.x86_64-linux = with pkgs;