crane for cached dep builds, clippy pedantic, extract paths module

flake.nix

@@ -4,6 +4,8 @@
   inputs = {
     nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
 
+    crane.url = "github:ipetkov/crane";
+
     treefmt-nix = {
       url = "github:numtide/treefmt-nix";
       inputs.nixpkgs.follows = "nixpkgs";
@@ -14,6 +16,7 @@
     {
       self,
       nixpkgs,
+      crane,
       treefmt-nix,
       ...
     }:
@@ -26,9 +29,31 @@
         f:
         nixpkgs.lib.genAttrs systems (
           system:
-          f {
+          let
             pkgs = nixpkgs.legacyPackages.${system};
-            treefmt-eval = treefmt-nix.lib.evalModule nixpkgs.legacyPackages.${system} treefmt-config;
+            craneLib = crane.mkLib pkgs;
+            src = craneLib.cleanCargoSource ./.;
+            commonArgs = {
+              inherit src;
+              pname = "damocles-daemon";
+              version = "0.1.0";
+              nativeBuildInputs = with pkgs; [ pkg-config ];
+              buildInputs = with pkgs; [
+                openssl
+                sqlite
+              ];
+            };
+            # deps-only build - cached separately, only rebuilds when Cargo.lock changes
+            cargoArtifacts = craneLib.buildDepsOnly commonArgs;
+          in
+          f {
+            inherit
+              pkgs
+              craneLib
+              commonArgs
+              cargoArtifacts
+              ;
+            treefmt-eval = treefmt-nix.lib.evalModule pkgs treefmt-config;
           }
         );
       treefmt-config = {
@@ -40,26 +65,24 @@
     in
     {
       packages = forAllSystems (
-        { pkgs, ... }:
         {
-          default = pkgs.rustPlatform.buildRustPackage {
-            pname = "damocles-daemon";
-            version = "0.1.0";
-            src = nixpkgs.lib.cleanSource ./.;
-            cargoLock.lockFile = ./Cargo.lock;
-
-            nativeBuildInputs = with pkgs; [ pkg-config ];
-            buildInputs = with pkgs; [
-              openssl
-              sqlite
-            ];
-
-            meta = {
-              description = "Matrix chat daemon for Damocles";
-              mainProgram = "damocles-daemon";
-              platforms = nixpkgs.lib.platforms.linux;
-            };
-          };
+          craneLib,
+          commonArgs,
+          cargoArtifacts,
+          ...
+        }:
+        {
+          default = craneLib.buildPackage (
+            commonArgs
+            // {
+              inherit cargoArtifacts;
+              meta = {
+                description = "Matrix chat daemon for Damocles";
+                mainProgram = "damocles-daemon";
+                platforms = nixpkgs.lib.platforms.linux;
+              };
+            }
+          );
         }
       );
 
@@ -84,10 +107,30 @@
       formatter = forAllSystems ({ treefmt-eval, ... }: treefmt-eval.config.build.wrapper);
 
       checks = forAllSystems (
-        { pkgs, treefmt-eval, ... }:
+        {
+          pkgs,
+          craneLib,
+          commonArgs,
+          cargoArtifacts,
+          treefmt-eval,
+          ...
+        }:
         {
           formatting = treefmt-eval.config.build.check self;
           build = self.packages.${pkgs.stdenv.hostPlatform.system}.default;
+          clippy = craneLib.cargoClippy (
+            commonArgs
+            // {
+              inherit cargoArtifacts;
+              cargoClippyExtraArgs = "--all-targets";
+            }
+          );
+          tests = craneLib.cargoTest (
+            commonArgs
+            // {
+              inherit cargoArtifacts;
+            }
+          );
         }
       );
     };