[nix] Extract Go derivation to nested flake for cross-repo reuse (#4406)

Author: maru-ava

flake.lock

@@ -9,10 +9,12 @@
   # Flake inputs
   inputs = {
     nixpkgs.url = "https://flakehub.com/f/NixOS/nixpkgs/0.2505.*.tar.gz";
+    go-flake.url = "path:./nix/go";
+    go-flake.inputs.nixpkgs.follows = "nixpkgs";
   };
 
   # Flake outputs
-  outputs = { self, nixpkgs }:
+  outputs = { self, nixpkgs, go-flake }:
     let
       # Systems supported
       allSystems = [
@@ -39,8 +41,8 @@
             # Task runner
             go-task
 
-            # Local Go package
-            (import ./nix/go.nix { inherit pkgs; })
+            # Local Go package from nested flake
+            go-flake.packages.${pkgs.system}.default
 
             # Monitoring tools
             promtail                                   # Loki log shipper

flake.nix

@@ -8,7 +8,7 @@ module github.com/ava-labs/avalanchego
 //   - CONTRIBUTING.md
 //   - README.md
 //   - go.mod (here)
-//   - nix/go.nix (update version and sha256 for supported arches)
+//   - nix/go/default.nix (update version and sha256 for supported arches)
 //   - tools/go.mod
 //
 // - If updating between minor versions (e.g. 1.24.x -> 1.25.x):

go.mod

@@ -0,0 +1,35 @@
+{
+  # To use locally: nix run ./nix/go
+  # To use remotely: nix run 'github:ava-labs/avalanchego?dir=nix/go'
+  # To use remotely at a specific revision: nix run 'github:ava-labs/avalanchego?dir=nix/go&ref=[SHA]'
+
+  description = "Go toolchain for Avalanche projects";
+
+  # Flake inputs
+  inputs = {
+    nixpkgs.url = "https://flakehub.com/f/NixOS/nixpkgs/0.2505.*.tar.gz";
+  };
+
+  # Flake outputs
+  outputs = { self, nixpkgs }:
+    let
+      # Systems supported
+      allSystems = [
+        "x86_64-linux" # 64-bit Intel/AMD Linux
+        "aarch64-linux" # 64-bit ARM Linux
+        "x86_64-darwin" # 64-bit Intel macOS
+        "aarch64-darwin" # 64-bit ARM macOS
+      ];
+
+      # Helper to provide system-specific attributes
+      forAllSystems = f: nixpkgs.lib.genAttrs allSystems (system: f {
+        pkgs = import nixpkgs { inherit system; };
+      });
+    in
+    {
+      # Export the Go package for other flakes to consume
+      packages = forAllSystems ({ pkgs }: {
+        default = import ./. { inherit pkgs; };
+      });
+    };
+}