project: perform clippy/rustfmt checking via a higher order derivation transformer

Instead of patching the derivation in-place via flags, we just have
a higher order function that takes the Rust package derivation and override it
into a Rustfmt / Clippy oriented derivation: it turns off checks and adds its
required dependencies.

flake.nix

@@ -62,12 +62,14 @@
           uefiPkgs = import nixpkgs {
             inherit system;
             crossSystem = {
-              config = "${pkgs.hostPlatform.linuxArch}-windows";
-              rustc.config = "${pkgs.hostPlatform.linuxArch}-unknown-uefi";
+              # linuxArch is wrong here, it will yield arm64 instead of aarch64.
+              config = "${pkgs.hostPlatform.qemuArch}-windows";
+              rustc.config = "${pkgs.hostPlatform.qemuArch}-unknown-uefi";
               libc = null;
               useLLVM = true;
             };
           };
+          utils = import ./nix/packages/utils.nix;
 
           inherit (pkgs) lib;
 
@@ -100,19 +102,21 @@
 
           overlayAttrs = { inherit (config.packages) tool; };
 
-          checks = let
+          checks =
+            let
               nixosLib = import (pkgs.path + "/nixos/lib") { };
               runTest = module:
                 nixosLib.runTest {
                   imports = [ module ];
                   hostPkgs = pkgs;
                 };
-          in {
-            toolFmt = (tool.override { enableFmt = true; });
-            stubFmt = (stub.override { enableFmt = true; });
-            toolClippy = (tool.override { enableLint = true; });
-            stubClippy = (stub.override { enableLint = true; });
-            fatStubClippy = (fatStub.override { enableLint = true; });
+            in
+            {
+              stubFmt = uefiPkgs.callPackage (utils.rustfmt stub) { };
+              toolFmt = pkgs.callPackage (utils.rustfmt tool) { };
+              toolClippy = pkgs.callPackage (utils.clippy tool) { };
+              stubClippy = uefiPkgs.callPackage (utils.clippy stub) { };
+              fatStubClippy = uefiPkgs.callPackage (utils.clippy fatStub) { };
             } // (import ./nix/tests/lanzaboote.nix {
               inherit pkgs;
               lanzabooteModule = self.nixosModules.lanzaboote;

nix/packages/stub.nix

@@ -1,31 +1,15 @@
-{ rust, rustPlatform, clippy, rustfmt, stdenv, lib, runCommand, enableFmt ? false, enableLint ? false, fatVariant ? false }:
+{ rustPlatform, stdenv, lib, fatVariant ? false }:
 
-let
-  targetSpec = rust.toRustTargetSpec stdenv.hostPlatform;
-  targetIsJSON = lib.hasSuffix ".json" targetSpec;
-  shortTarget =
-    if targetIsJSON then
-      (lib.removeSuffix ".json" (builtins.baseNameOf "${targetSpec}"))
-    else targetSpec;
-in
 rustPlatform.buildRustPackage
-  ({
+{
   pname = "lanzaboote_stub";
   version = "0.3.0";
-    src = runCommand "src" { } ''
-      install -D ${../../rust/stub/Cargo.toml} $out/Cargo.toml
-      install -D ${../../rust/stub/Cargo.lock} $out/Cargo.lock
-      cp -r ${../../rust/stub/src} $out/src
-    '';
+  src = lib.cleanSource ../../rust/stub;
 
   # We don't want the thin code.
   buildNoDefaultFeatures = true;
   buildFeatures = if fatVariant then [ "fat" ] else [ "thin" ];
 
-    # We don't want the thin code.
-    buildNoDefaultFeatures = fatVariant;
-    buildFeatures = lib.optional fatVariant "fat";
-
   cargoLock = {
     lockFile = ../../rust/stub/Cargo.lock;
   };
@@ -42,25 +26,4 @@ rustPlatform.buildRustPackage
     license = licenses.mit;
     platforms = [ "x86_64-windows" "aarch64-windows" "i686-windows" ];
   };
-  } // lib.optionalAttrs enableLint {
-    buildPhase = ''
-      cargo clippy --target ${shortTarget} --all-features -- -D warnings
-      if grep -R 'dbg!' ./src; then
-        echo "use of dbg macro found in code!"
-        false
-      fi
-    '';
-
-    installPhase = ''
-      touch $out
-    '';
-  } // lib.optionalAttrs enableFmt {
-    buildPhase = ''
-      echo "checking formatting..."
-      cargo fmt --all -- --check
-    '';
-
-    installPhase = ''
-      touch $out
-    '';
-  })
+}

nix/packages/tool.nix

@@ -1,31 +1,18 @@
-{ stdenv
-, systemd
+{ systemd
 , binutils-unwrapped
 , sbsigntool
 , rustPlatform
 , lib
-, runCommand
-, fetchurl
-, clippy
-, rustfmt
-, path
-, enableLint ? false
-, enableFmt ? false
 }:
+
 rustPlatform.buildRustPackage
-  ({
+{
   pname = "lanzaboote_tool";
   version = "0.3.0";
-    src = runCommand "src" { } ''
-      install -D ${../../rust/tool/Cargo.toml} $out/Cargo.toml
-      install -D ${../../rust/tool/Cargo.lock} $out/Cargo.lock
-      cp -r ${../../rust/tool/src} $out/src
-    '';
+  src = lib.cleanSource ../../rust/tool;
 
   TEST_SYSTEMD = systemd;
 
-    nativeBuildInputs = lib.optional enableLint clippy ++ lib.optional enableFmt rustfmt;
-
   cargoLock = {
     lockFile = ../../rust/tool/Cargo.lock;
   };
@@ -40,28 +27,4 @@ rustPlatform.buildRustPackage
     homepage = "https://github.com/nix-community/lanzaboote";
     license = licenses.mit;
   };
-  } // lib.optionalAttrs enableLint {
-    doCheck = false;
-    buildPhase = ''
-      cargo clippy --all-targets --all-features -- -D warnings
-      if grep -R 'dbg!' ./src; then
-        echo "use of dbg macro found in code!"
-        false
-      fi
-    '';
-
-    installPhase = ''
-      touch $out
-    '';
-  } // lib.optionalAttrs enableFmt {
-    doCheck = false;
-
-    buildPhase = ''
-      echo "checking formatting..."
-      cargo fmt --all -- --check
-    '';
-
-    installPhase = ''
-      touch $out
-    '';
-  })
+}

nix/packages/utils.nix

@@ -0,0 +1,39 @@
+{
+  clippy = rustPackage: { lib, rust, clippy }:
+    let
+      targetSpec = rust.toRustTargetSpec rustPackage.stdenv.hostPlatform;
+      inherit (lib) optionalString concatStringsSep;
+    in
+    rustPackage.overrideAttrs (old: {
+      nativeBuildInputs = (old.nativeBuildInputs or [ ]) ++ [ clippy ];
+
+      doCheck = false;
+
+      buildPhase = ''
+        echo "checking via clippy..."
+        cargo clippy --target ${targetSpec} ${optionalString (old.buildNoDefaultFeatures or false) "--no-default-features "}${optionalString ((old.buildFeatures or null) != null) ''--features="${concatStringsSep " " old.buildFeatures}" ''}-- -D warnings
+        if grep -R 'dbg!' ./src; then
+          echo "use of dbg macro found in code!"
+          false
+        fi
+      '';
+
+      installPhase = ''
+        touch $out
+      '';
+    });
+  rustfmt = rustPackage: { rustfmt }: rustPackage.overrideAttrs (old: {
+    nativeBuildInputs = (old.nativeBuildInputs or [ ]) ++ [ rustfmt ];
+
+    doCheck = false;
+
+    buildPhase = ''
+      echo "checking formatting..."
+      cargo fmt --all -- --check
+    '';
+
+    installPhase = ''
+      touch $out
+    '';
+  });
+}