nix: patch nix directly for experimental features

The bash wrapper was causing issues with deploy-rs and the
experimental-features option in the config was causing hercules-ci to
spit out a bunch of junk in the logs. Patching nix with the default
values required for flakes fixes both of these issues.

overlays/nixFlakes.nix

@@ -0,0 +1,8 @@
+final: prev: {
+  nixFlakes = prev.nixFlakes.overrideAttrs
+    (self: {
+      patches = [
+        ../pkgs/tools/package-management/nix/0001-nix-command-and-flakes-by-default.patch
+      ];
+    });
+}

pkgs/tools/package-management/nix/0001-nix-command-and-flakes-by-default.patch

@@ -0,0 +1,28 @@
+From a47bbae869ff35095eb2fe4d4d5145054ea81049 Mon Sep 17 00:00:00 2001
+From: Timothy DeHerrera <tim.deh@pm.me>
+Date: Wed, 17 Feb 2021 12:26:48 -0700
+Subject: [PATCH] nix-command and flakes by default
+
+---
+ src/libstore/globals.hh | 5 ++++-
+ 1 file changed, 4 insertions(+), 1 deletion(-)
+
+diff --git a/src/libstore/globals.hh b/src/libstore/globals.hh
+index eabd83e3f..e851e2a79 100644
+--- a/src/libstore/globals.hh
++++ b/src/libstore/globals.hh
+@@ -889,7 +889,10 @@ public:
+           value.
+           )"};
+
+-    Setting<Strings> experimentalFeatures{this, {}, "experimental-features",
++    Setting<Strings> experimentalFeatures{
++        this,
++        {"nix-command", "flakes", "ca-references"},
++        "experimental-features",
+         "Experimental Nix features to enable."};
+
+     bool isExperimentalFeatureEnabled(const std::string & name);
+--
+2.28.0
+

profiles/core/default.nix

@@ -138,10 +138,10 @@ in
     trustedUsers = [ "root" "@wheel" ];
 
     extraOptions = ''
-      experimental-features = nix-command flakes ca-references
       min-free = 536870912
       keep-outputs = true
       keep-derivations = true
+      fallback = true
     '';
 
   };

shell/default.nix

@@ -22,7 +22,7 @@ pkgs.devshell.mkShell
     nixos-install
     nixos-generate-config
     nixos-enter
-  ] ++ lib.optional (system == "x86_64-linux") pkgs.deploy-rs;
+  ];
 
   git.hooks = {
     pre-commit.text = lib.fileContents ./pre-commit.sh;
@@ -32,13 +32,11 @@ pkgs.devshell.mkShell
     {
       package = flk;
     }
-    {
-      name = "nix";
-      help = nixFlakes.meta.description;
-      command = ''
-        ${nixFlakes}/bin/nix --option experimental-features \
-          "nix-command flakes ca-references" "$@"
-      '';
-    }
-  ] ++ lib.optional (system != "i686-linux") { package = cachix; };
+  ]
+  ++ lib.optional (system != "i686-linux") { package = cachix; }
+  ++ lib.optional (system == "x86_64-linux") {
+    name = "deploy";
+    package = deploy-rs;
+    help = "A simple multi-profile Nix-flake deploy tool.";
+  };
 }

shell/devshell.toml

@@ -25,5 +25,8 @@ category = "documentation"
 package = "mdbook"
 category = "documentation"
 
+[[commands]]
+package = "nixFlakes"
+
 [git.hooks]
 enable = true