nix: partial incremental build of the router (#2416)

This is less incremental than crate2nix, but does build all dependencies
separately, so avoids full rebuilds.

_server.nix

-{ mkPoetryApplication, pkg-config, protobuf, openssl }:
+{
+  mkPoetryApplication,
+  pkg-config,
+  protobuf,
+  openssl,
+}:
 
 mkPoetryApplication {
   # name = "text-generation-server";

flake.lock

@@ -579,6 +579,27 @@
         "type": "github"
       }
     },
+    "naersk": {
+      "inputs": {
+        "nixpkgs": [
+          "tgi-nix",
+          "nixpkgs"
+        ]
+      },
+      "locked": {
+        "lastModified": 1721727458,
+        "narHash": "sha256-r/xppY958gmZ4oTfLiHN0ZGuQ+RSTijDblVgVLFi1mw=",
+        "owner": "nix-community",
+        "repo": "naersk",
+        "rev": "3fb418eaf352498f6b6c30592e3beb63df42ef11",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nix-community",
+        "repo": "naersk",
+        "type": "github"
+      }
+    },
     "nix-github-actions": {
       "inputs": {
         "nixpkgs": [
@@ -880,6 +901,7 @@
       "inputs": {
         "crate2nix": "crate2nix",
         "flake-utils": "flake-utils_6",
+        "naersk": "naersk",
         "nixpkgs": [
           "tgi-nix",
           "nixpkgs"

flake.nix

@@ -7,6 +7,10 @@
     tgi-nix.url = "github:danieldk/tgi-nix";
     nixpkgs.follows = "tgi-nix/nixpkgs";
     flake-utils.url = "github:numtide/flake-utils";
+    naersk = {
+      url = "github:nix-community/naersk";
+      inputs.nixpkgs.follows = "tgi-nix/nixpkgs";
+    };
     poetry2nix.url = "github:nix-community/poetry2nix";
     rust-overlay = {
       url = "github:oxalica/rust-overlay";
@@ -17,6 +21,7 @@
     {
       self,
       crate2nix,
+      naersk,
       nixpkgs,
       flake-utils,
       rust-overlay,
@@ -41,13 +46,32 @@
             tgi-nix.overlay
           ];
         };
+        naersk' = pkgs.callPackage naersk { };
+        router =
+          with pkgs;
+          naersk'.buildPackage {
+            name = "router";
+            src = ./.;
+            cargoBuildOptions =
+              x:
+              x
+              ++ [
+                "-p"
+                "text-generation-router-v3"
+              ];
+            nativeBuildInputs = [ pkg-config ];
+            buildInputs = [
+              openssl.dev
+              protobuf
+            ];
+            doCheck = false;
+          };
 
         inherit (poetry2nix.lib.mkPoetry2Nix { inherit pkgs; }) mkPoetryEditablePackage;
-        text-generation-server = mkPoetryEditablePackage {
-            editablePackageSources = ./server;
-        };
+        text-generation-server = mkPoetryEditablePackage { editablePackageSources = ./server; };
       in
       {
+        defaultPackage = router;
         devShells.default =
           with pkgs;
           mkShell {
@@ -93,10 +117,7 @@
                 vllm
 
                 cargoNix.workspaceMembers.text-generation-launcher.build
-
-                (callPackage ./router.nix {
-                  inherit (rustPlatform) buildRustPackage importCargoLock;
-                })
+                router
               ]);
 
             venvDir = "./.venv";

router.nix

-{ buildRustPackage, importCargoLock, pkg-config, protobuf, openssl }:
-
-buildRustPackage {
-  name = "text-generation-router";
-
-  src = ./.;
-
-  sourceDir = ./backends/v3;
-
-  cargoLock = {
-    lockFile = ./Cargo.lock;
-  };
-
-  nativeBuildInputs = [ pkg-config ];
-
-  buildInputs = [ openssl.dev protobuf ];
-
-}