pkgsets/rust: Fix rust overlay.

pkgsets/rustpkgs.nix

@@ -1,13 +1,39 @@
-{ config, pkgs, ... }:
+{ config, ... }:
 
 let
-  stablepkgs = import <nixos-stable> {};
+  mozRust = with builtins; (map (p: import ((fetchTarball {
+    url = "https://github.com/mozilla/nixpkgs-mozilla/archive/e912ed4.tar.gz";
+    sha256 = "08fvzb8w80bkkabc1iyhzd15f4sm7ra10jn32kfch5klgl0gj3j3";
+  }) + p))) [
+    (toPath "/lib-overlay.nix")
+    (toPath "/rust-overlay.nix")
+  ];
+  stablepkgs = import <nixos-stable> { overlays = mozRust;};
+
+  # https://rust-lang.github.io/rustup-components-history
+  nightly = stablepkgs.rustChannelOf {
+    date = "2020-06-10";
+    channel = "nightly";
+  };
+  rustNightly = {
+    rustc = nightly.rust.override {
+      extensions = [
+        "clippy-preview"
+        "rls-preview"
+        "rust-analysis"
+        "rust-src"
+        "rustfmt-preview"
+      ]; } // { src = nightly.rust-src; };
+    cargo = nightly.cargo;
+  };
+  rustPNightly = stablepkgs.recurseIntoAttrs (stablepkgs.makeRustPlatform  {
+    inherit (rustNightly) rustc cargo;
+  });
+
 in {
-  config.machine.pkgsets.rustpkgs.pkgs = with stablepkgs; [
+  config.machine.pkgsets.rustpkgs.pkgs = (with stablepkgs; [
     diesel-cli
-    rustup
-    rls
     carnix
     rustracer
-  ];
+  ]) ++ (with rustNightly; [ rustc cargo]);
 }