cosmic-bg: use mold linker

pkgs/by-name/co/cosmic-bg/package.nix

@@ -1,6 +1,7 @@
 {
   lib,
   stdenv,
+  stdenvAdapters,
   fetchFromGitHub,
   rustPlatform,
   just,
@@ -8,58 +9,65 @@
   makeBinaryWrapper,
   libxkbcommon,
   wayland,
+
+  withMoldLinker ? stdenv.targetPlatform.isLinux,
 }:
 
-rustPlatform.buildRustPackage rec {
-  pname = "cosmic-bg";
-  version = "1.0.0-alpha.6";
+rustPlatform.buildRustPackage.override
+  { stdenv = if withMoldLinker then stdenvAdapters.useMoldLinker stdenv else stdenv; }
+  rec {
+    pname = "cosmic-bg";
+    version = "1.0.0-alpha.6";
 
-  src = fetchFromGitHub {
-    owner = "pop-os";
-    repo = pname;
-    rev = "epoch-${version}";
-    hash = "sha256-4b4laUXTnAbdngLVh8/dD144m9QrGReSEjRZoNR6Iks=";
-  };
+    src = fetchFromGitHub {
+      owner = "pop-os";
+      repo = pname;
+      rev = "epoch-${version}";
+      hash = "sha256-4b4laUXTnAbdngLVh8/dD144m9QrGReSEjRZoNR6Iks=";
+    };
 
-  useFetchCargoVendor = true;
-  cargoHash = "sha256-GLXooTjcGq4MsBNnlpHBBUJGNs5UjKMQJGJuj9UO2wk=";
+    useFetchCargoVendor = true;
+    cargoHash = "sha256-GLXooTjcGq4MsBNnlpHBBUJGNs5UjKMQJGJuj9UO2wk=";
 
-  postPatch = ''
-    substituteInPlace justfile --replace-fail '#!/usr/bin/env' "#!$(command -v env)"
-  '';
+    postPatch = ''
+      substituteInPlace justfile --replace-fail '#!/usr/bin/env' "#!$(command -v env)"
+    '';
 
-  nativeBuildInputs = [
-    just
-    pkg-config
-    makeBinaryWrapper
-  ];
-  buildInputs = [
-    libxkbcommon
-    wayland
-  ];
+    nativeBuildInputs = [
+      just
+      pkg-config
+      makeBinaryWrapper
+    ];
+    buildInputs = [
+      libxkbcommon
+      wayland
+    ];
 
-  dontUseJustBuild = true;
+    dontUseJustBuild = true;
 
-  justFlags = [
-    "--set"
-    "prefix"
-    (placeholder "out")
-    "--set"
-    "bin-src"
-    "target/${stdenv.hostPlatform.rust.cargoShortTarget}/release/cosmic-bg"
-  ];
+    justFlags = [
+      "--set"
+      "prefix"
+      (placeholder "out")
+      "--set"
+      "bin-src"
+      "target/${stdenv.hostPlatform.rust.cargoShortTarget}/release/cosmic-bg"
+    ];
 
-  postInstall = ''
-    wrapProgram $out/bin/cosmic-bg \
-      --prefix LD_LIBRARY_PATH : "${lib.makeLibraryPath [ wayland ]}"
-  '';
+    env."CARGO_TARGET_${stdenv.hostPlatform.rust.cargoEnvVarTarget}_RUSTFLAGS" =
+      lib.optionalString withMoldLinker "-C link-arg=-fuse-ld=mold";
 
-  meta = with lib; {
-    homepage = "https://github.com/pop-os/cosmic-bg";
-    description = "Applies Background for the COSMIC Desktop Environment";
-    license = licenses.mpl20;
-    maintainers = with maintainers; [ nyabinary ];
-    platforms = platforms.linux;
-    mainProgram = "cosmic-bg";
-  };
-}
+    postInstall = ''
+      wrapProgram $out/bin/cosmic-bg \
+        --prefix LD_LIBRARY_PATH : "${lib.makeLibraryPath [ wayland ]}"
+    '';
+
+    meta = with lib; {
+      homepage = "https://github.com/pop-os/cosmic-bg";
+      description = "Applies Background for the COSMIC Desktop Environment";
+      license = licenses.mpl20;
+      maintainers = with maintainers; [ nyabinary ];
+      platforms = platforms.linux;
+      mainProgram = "cosmic-bg";
+    };
+  }