Update nix to nix 2.13

dep/nixpkgs_unstable/default.nix

@@ -0,0 +1,2 @@
+# DO NOT HAND-EDIT THIS FILE
+import (import ./thunk.nix)

dep/nixpkgs_unstable/github.json

@@ -0,0 +1,7 @@
+{
+  "owner": "NixOS",
+  "repo": "nixpkgs",
+  "private": false,
+  "rev": "22ce075f1c3ffb413dfc53b10ff3e577b5b15941",
+  "sha256": "1pgxmdw7qi5kq1jn9fq1jfv757y67rfgkid2zkip8licyghlgdr1"
+}

dep/nixpkgs_unstable/thunk.nix

@@ -0,0 +1,12 @@
+# DO NOT HAND-EDIT THIS FILE
+let fetch = { private ? false, fetchSubmodules ? false, owner, repo, rev, sha256, ... }:
+  if !fetchSubmodules && !private then builtins.fetchTarball {
+    url = "https://github.com/${owner}/${repo}/archive/${rev}.tar.gz"; inherit sha256;
+  } else (import (builtins.fetchTarball {
+  url = "https://github.com/NixOS/nixpkgs/archive/3aad50c30c826430b0270fcf8264c8c41b005403.tar.gz";
+  sha256 = "0xwqsf08sywd23x0xvw4c4ghq0l28w2ki22h0bdn766i16z9q2gr";
+}) {}).fetchFromGitHub {
+    inherit owner repo rev sha256 fetchSubmodules private;
+  };
+  json = builtins.fromJSON (builtins.readFile ./github.json);
+in fetch json

haskell-overlays/obelisk.nix

@@ -20,7 +20,7 @@ in
     librarySystemDepends = [
       pkgs.jre
       pkgs.git
-      pkgs.nix
+      pkgs.nixpkgs_unstable.nixVersions.nix_2_13
       pkgs.nix-prefetch-git
       pkgs.openssh
       pkgs.rsync
@@ -38,7 +38,7 @@ in
       pkgs.cabal-install
       pkgs.coreutils
       pkgs.git
-      pkgs.nix
+      pkgs.nixpkgs_unstable.nixVersions.nix_2_13
       pkgs.nix-prefetch-git
       pkgs.rsync
     ];

lib/command/src/Obelisk/Command/Project.hs

@@ -301,7 +301,7 @@ filePermissionIsSafe s umask = not fileWorldWritable && fileGroupWritable <= uma
 nixShellRunConfig :: MonadObelisk m => FilePath -> Bool -> Maybe String -> m NixShellConfig
 nixShellRunConfig root isPure command = do
   nixpkgsPath <- fmap T.strip $ readProcessAndLogStderr Debug $ setCwd (Just root) $
-    proc nixExePath ["eval", "(import .obelisk/impl {}).nixpkgs.path"]
+    proc nixExePath ["eval", "--impure", "--expr", "(import .obelisk/impl {}).nixpkgs.path"]
   nixRemote <- liftIO $ lookupEnv "NIX_REMOTE"
   pure $ def
     & nixShellConfig_pure .~ isPure
@@ -383,8 +383,12 @@ findProjectAssets root = do
   isDerivation <- readProcessAndLogStderr Debug $ setCwd (Just root) $
     proc nixExePath
       [ "eval"
+      , "--impure"
+      , "--expr"
       , "(let a = import ./. {}; in toString (a.reflex.nixpkgs.lib.isDerivation a.passthru.staticFilesImpure))"
       , "--raw"
+      -- `--expr` and `--impure` are a side-effect of a newer nix version
+      -- `nix eval` is no longer the same as 2.3
       -- `--raw` is not available with old nix-instantiate. It drops quotation
       -- marks and trailing newline, so is very convenient for shelling out.
       ]

nixpkgs-overlays/default.nix

@@ -12,4 +12,6 @@ in {
     lib.cleanSource (gitignoreSource src);
 
   obeliskExecutableConfig = self.callPackage ../lib/executable-config {};
+
+  nixpkgs_unstable = import ../dep/nixpkgs_unstable { };
 }