build(nix): use nix-cargo-integration, make shell.nix use flake devshell

.envrc

@@ -1,2 +1,5 @@
 watch_file shell.nix
-use flake
+watch_file flake.lock
+
+# try to use flakes, if it fails use normal nix (ie. shell.nix)
+use flake || use nix

flake.nix

@@ -3,54 +3,54 @@
 
   inputs = {
     nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable";
-    flake-utils.url = "github:numtide/flake-utils";
-    rust-overlay.url = "github:oxalica/rust-overlay";
-    naersk.url = "github:nmattia/naersk";
-    helix = {
+    nixCargoIntegration = {
+      url = "github:yusdacra/nix-cargo-integration";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
+    flakeCompat = {
+      url = "github:edolstra/flake-compat";
       flake = false;
-      url = "https://github.com/helix-editor/helix";
+    };
+    helix = {
+      url = "https://github.com/helix-editor/helix.git";
       type = "git";
+      flake = false;
       submodules = true;
     };
   };
 
-  outputs = inputs@{ self, nixpkgs, naersk, rust-overlay, flake-utils, ... }:
-    let
-      rust = pkgs:
-        (pkgs.rustChannelOf {
-          date = "2021-05-01";
-          channel = "nightly";
-        }).minimal; # cargo, rustc and rust-std
-
-      mkNaerskLib = system: pkgs:
-        naersk.lib."${system}".override {
-          # naersk can't build with stable?!
-          # inherit (pkgs.rust-bin.stable.latest) rustc cargo;
-          rustc = rust pkgs;
-          cargo = rust pkgs;
+  outputs = inputs@{ nixCargoIntegration, helix, ... }:
+    nixCargoIntegration.lib.makeOutputs {
+      root = ./.;
+      buildPlatform = "crate2nix";
+      renameOutputs = { "helix-term" = "helix"; };
+      # Set default app to hx (binary is from helix-term release build)
+      # Set default package to helix-term release build
+      defaultOutputs = { app = "hx"; package = "helix"; };
+      overrides = {
+        crateOverrides = common: _: {
+          helix-term = prev: { buildInputs = (prev.buildInputs or [ ]) ++ [ common.cCompiler.cc.lib ]; };
+          # link runtime since helix-core expects it because of embed_runtime feature
+          helix-core = _: { preConfigure = "ln -s ${common.root + "/runtime"} ../runtime"; };
+          # link languages and theme toml files since helix-view expects them
+          helix-view = _: { preConfigure = "ln -s ${common.root}/{languages.toml,theme.toml} .."; };
+          helix-syntax = prev: {
+            src = common.pkgs.runCommand prev.src.name { } ''
+              mkdir -p $out
+              ln -s ${prev.src}/* $out
+              ln -sf ${helix}/helix-syntax/languages $out
+            '';
+          };
         };
-
-      pkg = naerskLib:
-        naerskLib.buildPackage {
-          pname = "helix";
-          root = inputs.helix;
-          cargoBuildOptions = self: self ++ [ ''--features "embed_runtime"'' ];
+        shell = common: prev: {
+          packages = prev.packages ++ (with common.pkgs; [ lld_10 lldb ]);
+          env = prev.env ++ [
+            { name = "HELIX_RUNTIME"; eval = "$PWD/runtime"; }
+            { name = "RUST_BACKTRACE"; value = "1"; }
+            { name = "RUSTFLAGS"; value = "-C link-arg=-fuse-ld=lld -C target-cpu=native"; }
+          ];
         };
-
-    in flake-utils.lib.eachDefaultSystem (system:
-      let
-        pkgs = import nixpkgs {
-          inherit system;
-          overlays = [ rust-overlay.overlay ];
-        };
-        naerskLib = mkNaerskLib system pkgs;
-      in rec {
-        packages.helix = pkg naerskLib;
-        defaultPackage = packages.helix;
-        devShell = pkgs.callPackage ./shell.nix { };
-      }) // {
-        overlay = final: prev:
-          let naerskLib = mkNaerskLib prev.system final;
-          in (rust-overlay.overlay final prev) // { helix = pkg naerskLib; };
+        build = _: prev: { rootFeatures = prev.rootFeatures ++ [ "embed_runtime" ]; };
       };
+    };
 }

helix-term/Cargo.toml

@@ -6,7 +6,9 @@ authors = ["Blaž Hrastnik <blaz@mxxn.io>"]
 edition = "2018"
 license = "MPL-2.0"
 
-# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+[package.metadata.nix]
+build = true
+app = true
 
 [features]
 embed_runtime = ["helix-core/embed_runtime"]

shell.nix

@@ -1,22 +1,6 @@
-{ lib, stdenv, pkgs }:
-
-pkgs.mkShell {
-  nativeBuildInputs = with pkgs; [
-    (rust-bin.stable.latest.default.override { extensions = ["rust-src"]; })
-    lld_10
-    lldb
-    # pythonPackages.six
-    stdenv.cc.cc.lib
-    # pkg-config
-  ];
-  RUSTFLAGS = "-C link-arg=-fuse-ld=lld -C target-cpu=native";
-  RUST_BACKTRACE = "1";
-  # https://github.com/rust-lang/rust/issues/55979
-  LD_LIBRARY_PATH = lib.makeLibraryPath (with pkgs; [
-    stdenv.cc.cc.lib
-  ]);
-
-  shellHook = ''
-    export HELIX_RUNTIME=$PWD/runtime
-  '';
-}
+# Flake's devShell for non-flake-enabled nix instances
+let
+  src = (builtins.fromJSON (builtins.readFile ./flake.lock)).nodes.flakeCompat.locked;
+  compat = fetchTarball { url = "https://github.com/edolstra/flake-compat/archive/${src.rev}.tar.gz"; sha256 = src.narHash; };
+in
+(import compat { src = ./.; }).shellNix.default