build(nix): package diffcore-web as its own derivation

default.nix

@@ -21,10 +21,13 @@
   pango,
   webkitgtk_4_1,
   zlib,
+  # `desktop` and `web` are mutually exclusive cargo features (see
+  # diffcore-tauri/src/lib.rs), so diffcore-web needs its own derivation.
+  webMode ? false,
 }:
 
 rustPlatform.buildRustPackage {
-  pname = "diff-core";
+  pname = if webMode then "diffcore-web" else "diff-core";
   version = (lib.importTOML ./Cargo.toml).workspace.package.version;
   __structuredAttrs = true;
 
@@ -40,25 +43,31 @@ rustPlatform.buildRustPackage {
 
   nativeBuildInputs = [
     pkg-config
-    wrapGAppsHook3
     nodejs
     npmHooks.npmConfigHook
+  ]
+  ++ lib.optionals (!webMode) [
+    wrapGAppsHook3
     copyDesktopItems
   ];
 
+  # The web server is a plain axum binary; only the desktop app needs the
+  # gtk/webkit stack.
   buildInputs = [
+    libgit2
+    oniguruma
+    openssl
+    zlib
+  ]
+  ++ lib.optionals (!webMode) [
     atk
     cairo
     gdk-pixbuf
     glib
     gtk3
-    libgit2
     libsoup_3
-    oniguruma
-    openssl
     pango
     webkitgtk_4_1
-    zlib
   ];
 
   env = {
@@ -70,15 +79,35 @@ rustPlatform.buildRustPackage {
     npm --prefix crates/diffcore-tauri/ui run build
   '';
 
-  # Desktop app + CLI (production webview assets). The `web` feature is
-  # mutually exclusive with `desktop` upstream, so diffcore-web needs its
-  # own derivation.
-  cargoBuildFlags = [
+  # Desktop app + CLI (production webview assets), or the standalone web
+  # server. `--no-default-features` is scoped to diffcore-tauri via `-p` so it
+  # does not strip defaults from the rest of the workspace.
+  cargoBuildFlags =
+    if webMode then
+      [
+        "-p"
+        "diffcore-tauri"
+        "--no-default-features"
+        "--features"
+        "web"
+      ]
+    else
+      [
+        "--features"
+        "diffcore-tauri/custom-protocol"
+      ];
+
+  # Default cargoTestFlags would test the whole workspace with default
+  # features, pulling `desktop` back in without gtk/webkit present.
+  cargoTestFlags = lib.optionals webMode [
+    "-p"
+    "diffcore-tauri"
+    "--no-default-features"
     "--features"
-    "diffcore-tauri/custom-protocol"
+    "web"
   ];
 
-  desktopItems = [
+  desktopItems = lib.optionals (!webMode) [
     (makeDesktopItem {
       name = "diffcore-tauri";
       exec = "diffcore-tauri";
@@ -94,9 +123,12 @@ rustPlatform.buildRustPackage {
     })
   ];
 
+  # Both binaries resolve the UI from ../share/diffcore/ui relative to $out/bin.
   postInstall = ''
     mkdir -p $out/share/diffcore
     cp -r crates/diffcore-tauri/ui/dist $out/share/diffcore/ui
+  ''
+  + lib.optionalString (!webMode) ''
     for size in 32 64 128; do
       install -Dm444 crates/diffcore-tauri/icons/''${size}x''${size}.png \
         $out/share/icons/hicolor/''${size}x''${size}/apps/diffcore-tauri.png
@@ -118,9 +150,13 @@ rustPlatform.buildRustPackage {
   '';
 
   meta = {
-    description = "Semantic diff layer for code review";
+    description =
+      if webMode then
+        "Semantic diff layer for code review (web server)"
+      else
+        "Semantic diff layer for code review";
     homepage = "https://github.com/jamesaphoenix/diff-core";
     license = lib.licenses.mit;
-    mainProgram = "diffcore";
+    mainProgram = if webMode then "diffcore-web" else "diffcore";
   };
 }

flake.nix

@@ -13,14 +13,16 @@
       ];
       forAllSystems = f: nixpkgs.lib.genAttrs systems (system: f nixpkgs.legacyPackages.${system});
       diffCoreFor = pkgs: pkgs.callPackage ./default.nix { };
+      diffCoreWebFor = pkgs: pkgs.callPackage ./default.nix { webMode = true; };
     in
     {
       packages = forAllSystems (pkgs: rec {
         diff-core = diffCoreFor pkgs;
+        diffcore-web = diffCoreWebFor pkgs;
         default = diff-core;
       });
 
-      # The two modes: `nix run .#cli|desktop`
+      # The three modes: `nix run .#cli|desktop|web`
       apps = forAllSystems (
         pkgs:
         let
@@ -33,6 +35,10 @@
         rec {
           cli = app "diffcore";
           desktop = app "diffcore-tauri";
+          web = {
+            type = "app";
+            program = "${diffCoreWebFor pkgs}/bin/diffcore-web";
+          };
           default = desktop;
         }
       );