feat: patch nix repl command

Author: aiotter

default.nix

@@ -4,6 +4,7 @@
   imports = [
     modules/nix-conf.nix
     modules/snmp
+    modules/nix-cli
   ];
 
   system.primaryUser = "aiotter";

flake.lock

@@ -4,6 +4,7 @@
   inputs = {
     determinate.url = "https://flakehub.com/f/DeterminateSystems/determinate/3";
     nixpkgs.follows = "determinate/nixpkgs";
+    nix-src.follows = "determinate/nix";
     darwin = {
       url = "github:lnl7/nix-darwin/master";
       inputs.nixpkgs.follows = "nixpkgs";
@@ -17,7 +18,7 @@
   };
 
   outputs =
-    flakeInputs@{ self, nixpkgs, darwin, determinate, mac-app-util }:
+    flakeInputs@{ self, nixpkgs, nix-src, darwin, determinate, mac-app-util }:
     let
       inherit (nixpkgs) lib;
       darwinSystems = lib.systems.doubles.darwin;
@@ -35,7 +36,7 @@
               mac-app-util.darwinModules.default
               ./.
             ];
-            specialArgs = { inherit flakeInputs; };
+            specialArgs = { inherit flakeInputs system; };
           };
         in
         {

flake.nix

@@ -0,0 +1,34 @@
+{
+  lib,
+  flakeInputs,
+  system,
+  ...
+}:
+
+let
+  patchNixCmd =
+    dep:
+    if lib.hasSuffix "nix-cmd" dep.pname then
+      dep.overrideAttrs (
+        prev:
+        assert !(prev ? patches);
+        {
+          patches = [ ./nix-repl-prebind-pkgs.patch ];
+          patchFlags = [ "-p1" "-d" "../.." ];
+        }
+      )
+    else
+      dep;
+
+  patchDeps = deps: builtins.map patchNixCmd deps;
+
+  nix-cli = flakeInputs.nix-src.packages.${system}.nix-cli.overrideAttrs (prev: {
+    buildInputs = patchDeps (prev.buildInputs or [ ]);
+    nativeBuildInputs = patchDeps (prev.nativeBuildInputs or [ ]);
+    propagatedBuildInputs = patchDeps (prev.propagatedBuildInputs or [ ]);
+  });
+in
+
+{
+  environment.systemPackages = [ nix-cli ];
+}

modules/nix-cli/default.nix

@@ -0,0 +1,22 @@
+diff --git a/src/libcmd/repl.cc b/src/libcmd/repl.cc
+index 841c75737..82a51838a 100644
+--- a/src/libcmd/repl.cc
++++ b/src/libcmd/repl.cc
+@@ -770,6 +770,17 @@ void NixRepl::initEnv()
+     varNames.clear();
+     for (auto & i : state->staticBaseEnv->vars)
+         varNames.emplace(state->symbols[i.first]);
++
++    // Pre-bind pkgs for convenience (best-effort).
++    // Keep the REPL usable even if <nixpkgs> is missing.
++    notice("Binding pkgs...");
++    try {
++        processLine("pkgs = import <nixpkgs> {}");
++    } catch (const Error &e) {
++        warn("failed to initialize pkgs: %s", e.what());
++    } catch (...) {
++        warn("failed to initialize pkgs (unknown error)");
++    }
+ }
+ 
+ void NixRepl::showLastLoaded()