nix: Separate debug output (#27871)

This makes it easier to iterate on the nix flake by adding a package
which builds zed in debug mode rather than release

Release Notes:

- N/A

flake.nix

@@ -26,41 +26,30 @@
         "aarch64-darwin"
       ];
 
-      overlays = {
-        rust-overlay = rust-overlay.overlays.default;
-        rust-toolchain = final: prev: {
-          rustToolchain = final.rust-bin.fromRustupToolchainFile ./rust-toolchain.toml;
-        };
-        zed-editor = final: prev: {
-          zed-editor = final.callPackage ./nix/build.nix {
-            crane = crane.mkLib final;
-            rustToolchain = final.rustToolchain;
-          };
-        };
-      };
-
-      mkPkgs =
-        system:
-        import nixpkgs {
-          inherit system;
-          overlays = builtins.attrValues overlays;
-        };
-
-      forAllSystems = f: nixpkgs.lib.genAttrs systems (system: f (mkPkgs system));
+      forAllSystems = f: nixpkgs.lib.genAttrs systems (system: f nixpkgs.legacyPackages.${system});
+      mkZed =
+        pkgs:
+        let
+          rustBin = rust-overlay.lib.mkRustBin { } pkgs;
         in
-    {
-      packages = forAllSystems (pkgs: {
-        default = pkgs.zed-editor;
+        pkgs.callPackage ./nix/build.nix {
+          crane = crane.mkLib pkgs;
+          rustToolchain = rustBin.fromRustupToolchainFile ./rust-toolchain.toml;
+        };
+    in
+    rec {
+      packages = forAllSystems (pkgs: rec {
+        default = mkZed pkgs;
+        debug = default.override { profile = "dev"; };
       });
-
       devShells = forAllSystems (pkgs: {
-        default = pkgs.callPackage ./nix/shell.nix { };
+        default = pkgs.callPackage ./nix/shell.nix {
+          zed-editor = packages.${pkgs.hostPlatform.system}.default;
+        };
       });
-
       formatter = forAllSystems (pkgs: pkgs.nixfmt-rfc-style);
-
-      overlays = overlays // {
-        default = nixpkgs.lib.composeManyExtensions (builtins.attrValues overlays);
+      overlays.default = final: _: {
+        zed-editor = mkZed final;
       };
     };
 

nix/shell.nix

@@ -1,5 +1,4 @@
 {
-  lib,
   mkShell,
   stdenv,
   stdenvAdapters,