build(nix): add mold to the flake dev shell (#2122)

.github/workflows/nix.yml

@@ -6,12 +6,14 @@ on:
     paths:
       - "**/*.nix"
       - "flake.lock"
+      - "rust-toolchain.toml"
   pull_request:
     branches: ["main", "develop"]
     types: [opened, synchronize, reopened, ready_for_review]
     paths:
       - "**/*.nix"
       - "flake.lock"
+      - "rust-toolchain.toml"
 
 concurrency:
   group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}
@@ -32,5 +34,11 @@ jobs:
       - name: Magic Nix Cache
         uses: DeterminateSystems/magic-nix-cache-action@v6
 
-      - name: Check full devShell
+      - name: Warm up full devShell
         run: nix develop .#full --command true
+
+      - name: Cargo check in flake environment
+        run: nix develop .#full --command cargo check
+
+      - name: Cargo build in flake environment
+        run: nix develop .#full --command cargo build

flake.nix

@@ -67,6 +67,7 @@
                   rust
                   protobuf
                   clang
+                  mold
                   pkg-config
                   bridge-utils # for three node test
                 ]
@@ -98,6 +99,10 @@
             KCP_SYS_EXTRA_HEADER_PATH = "${pkgs.libclang.lib}/lib/clang/19/include:${pkgs.glibc.dev}/include";
             JEMALLOC_OVERRIDE = "${pkgs.jemalloc}/lib/libjemalloc.so";
           }
+          // pkgs.lib.optionalAttrs pkgs.stdenv.isLinux {
+            CARGO_TARGET_X86_64_UNKNOWN_LINUX_GNU_LINKER = "clang";
+            CARGO_TARGET_AARCH64_UNKNOWN_LINUX_GNU_LINKER = "clang";
+          }
           // (if hasFeature "android" then android.envVars else { }));
       in
       {