Add a crane build for incremental builds?

.gitignore

@@ -1,3 +1,4 @@
+/result
 /target
 /.direnv
 /.pre-commit-config.yaml

flake.lock

@@ -1,5 +1,25 @@
 {
   "nodes": {
+    "crane": {
+      "inputs": {
+        "nixpkgs": [
+          "nixpkgs"
+        ]
+      },
+      "locked": {
+        "lastModified": 1721842668,
+        "narHash": "sha256-k3oiD2z2AAwBFLa4+xfU+7G5fisRXfkvrMTCJrjZzXo=",
+        "owner": "ipetkov",
+        "repo": "crane",
+        "rev": "529c1a0b1f29f0d78fa3086b8f6a134c71ef3aaf",
+        "type": "github"
+      },
+      "original": {
+        "owner": "ipetkov",
+        "repo": "crane",
+        "type": "github"
+      }
+    },
     "flake-compat": {
       "flake": false,
       "locked": {
@@ -94,8 +114,30 @@
     },
     "root": {
       "inputs": {
+        "crane": "crane",
         "git-hooks": "git-hooks",
-        "nixpkgs": "nixpkgs"
+        "nixpkgs": "nixpkgs",
+        "rust-overlay": "rust-overlay"
+      }
+    },
+    "rust-overlay": {
+      "inputs": {
+        "nixpkgs": [
+          "nixpkgs"
+        ]
+      },
+      "locked": {
+        "lastModified": 1722391647,
+        "narHash": "sha256-JTi7l1oxnatF1uX/gnGMlRnyFMtylRw4MqhCUdoN2K4=",
+        "owner": "oxalica",
+        "repo": "rust-overlay",
+        "rev": "0fd4a5d2098faa516a9b83022aec7db766cd1de8",
+        "type": "github"
+      },
+      "original": {
+        "owner": "oxalica",
+        "repo": "rust-overlay",
+        "type": "github"
       }
     }
   },

flake.nix

@@ -3,10 +3,16 @@
     nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
     git-hooks.url = "github:cachix/git-hooks.nix";
     git-hooks.inputs.nixpkgs.follows = "nixpkgs";
+    crane.url = "github:ipetkov/crane";
+    crane.inputs.nixpkgs.follows = "nixpkgs";
+    rust-overlay.url = "github:oxalica/rust-overlay";
+    rust-overlay.inputs.nixpkgs.follows = "nixpkgs";
   };
   outputs = {
     self,
     git-hooks,
+    rust-overlay,
+    crane,
     nixpkgs,
   }: let
     inherit (self) outputs;
@@ -14,7 +20,7 @@
 
     systems = ["aarch64-linux" "aarch64-darwin" "x86_64-darwin" "x86_64-linux"];
     forSystems = nixpkgs.lib.genAttrs systems;
-    pkgsFor = system: (import nixpkgs {inherit system;}).extend overlays.default;
+    pkgsFor = system: ((import nixpkgs {inherit system;}).extend overlays.default).extend rust-overlay.overlays.default;
     genPkgs = func: (forSystems (system: func (pkgsFor system)));
     buildTimeDeps = pkgs:
       with pkgs; [
@@ -61,8 +67,68 @@
       build = outputs.packages.${pkgs.system}.default;
     });
 
-    packages = genPkgs (pkgs: {
-      kodotag = pkgs.rustPlatform.buildRustPackage {
+    packages = genPkgs (pkgs: let
+      rustToolchainFor = p:
+        p.rust-bin.selectLatestNightlyWith (toolchain:
+          toolchain.default.override {
+            extensions = ["rust-src"];
+            targets = ["x86_64-unknown-linux-gnu"];
+          });
+      rustToolchain = rustToolchainFor pkgs;
+      craneLib = (crane.mkLib pkgs).overrideToolchain rustToolchainFor;
+
+      src = let
+        # per https://github.com/ipetkov/crane/blob/529c1a0b1f29f0d78fa3086b8f6a134c71ef3aaf/docs/source-filtering.md we need the font file since we bake it into the binary as the default bevy font
+        fontFilter = path: _type: builtins.match ".*ttf$" path != null;
+        filteredSources = path: type:
+          (fontFilter path type) || (craneLib.filterCargoSources path type);
+      in
+        pkgs.lib.cleanSourceWith {
+          src = ./.; # The original, unfiltered source
+
+          filter = filteredSources;
+          name = "source"; # Be reproducible, regardless of the directory name
+        };
+    in {
+      kodotag = craneLib.buildPackage {
+        # TODO: incremental rust builds with nix would be awesome
+        pname = "kodotag";
+        version = "0.1.0";
+
+        inherit src;
+        strictDeps = true;
+        cargoVendorDir = craneLib.vendorMultipleCargoDeps {
+          inherit (craneLib.findCargoFiles src) cargoConfigs;
+          cargoLockList = [
+            ./Cargo.lock
+
+            # Unfortunately this approach requires IFD (import-from-derivation)
+            # otherwise Nix will refuse to read the Cargo.lock from our toolchain
+            # (unless we build with `--impure`).
+            #
+            # Another way around this is to manually copy the rustlib `Cargo.lock`
+            # to the repo and import it with `./path/to/rustlib/Cargo.lock` which
+            # will avoid IFD entirely but will require manually keeping the file
+            # up to date!
+            "${rustToolchain.passthru.availableComponents.rust-src}/lib/rustlib/src/rust/Cargo.lock"
+          ];
+        };
+        # cargoExtraArgs = "-Z build-std --target x86_64-unknown-linux-gnu";
+
+        nativeBuildInputs = buildTimeDeps pkgs;
+        buildInputs = linkTimeDeps pkgs;
+        hash = pkgs.lib.fakeHash;
+        # cargoHash = "";
+        cargoHash = "sha256-d7luBIWHWn2ZpmSnIgpuLXsy1URUIojpPFboMtqa2ps=";
+
+        # a hack to avoid using mold as our linker when building with nix
+        postUnpack = ''
+          ls -la
+          rm -r ./*/.cargo
+        '';
+      };
+
+      kodotag-no-crane = pkgs.rustPlatform.buildRustPackage {
         pname = "kodotag";
         version = "0.1.0";
         nativeBuildInputs = buildTimeDeps pkgs;
@@ -79,7 +145,7 @@
         '';
       };
 
-      default = outputs.packages.${pkgs.system}.kodotag;
+      default = outputs.packages.${pkgs.system}.kodotag-no-crane;
     });
 
     devShells = genPkgs (pkgs: {