push sheeet

nixos/modules/tasks/filesystems/envfs.nix

@@ -0,0 +1,78 @@
+{
+  pkgs,
+  config,
+  lib,
+  ...
+}:
+
+let
+  cfg = config.services.envfs;
+  mounts = {
+    "/usr/bin" = {
+      device = "none";
+      fsType = "envfs";
+      options = [
+        "bind-mount=/bin"
+        "fallback-path=${
+          pkgs.runCommand "fallback-path" { } (
+            ''
+              mkdir -p $out
+              ln -s ${config.environment.usrbinenv} $out/env
+              ln -s ${config.environment.binsh} $out/sh
+            ''
+            + cfg.extraFallbackPathCommands
+          )
+        }"
+        "nofail"
+      ];
+    };
+    # We need to bind-mount /bin to /usr/bin, because otherwise upgrading
+    # from envfs < 1.0.5 will cause having the old envs with no /bin bind mount.
+    # Systemd is smart enough to not mount /bin if it's already mounted.
+    "/bin" = {
+      device = "/usr/bin";
+      fsType = "none";
+      options = [
+        "bind"
+        "nofail"
+      ];
+    };
+  };
+in
+{
+  options = {
+    services.envfs = {
+      enable = lib.mkEnableOption "Envfs filesystem" // {
+        description = ''
+          Fuse filesystem that returns symlinks to executables based on the PATH
+          of the requesting process. This is useful to execute shebangs on NixOS
+          that assume hard coded locations in locations like /bin or /usr/bin
+          etc.
+        '';
+      };
+
+      package = lib.mkOption {
+        type = lib.types.package;
+        default = pkgs.envfs;
+        defaultText = lib.literalExpression "pkgs.envfs";
+        description = "Which package to use for the envfs.";
+      };
+
+      extraFallbackPathCommands = lib.mkOption {
+        type = lib.types.lines;
+        default = "";
+        example = "ln -s $''{pkgs.bash}/bin/bash $out/bash";
+        description = "Extra commands to run in the package that contains fallback executables in case not other executable is found";
+      };
+    };
+  };
+  config = lib.mkIf (cfg.enable) {
+    environment.systemPackages = [ cfg.package ];
+    # we also want these mounts in virtual machines.
+    fileSystems = if config.virtualisation ? qemu then lib.mkVMOverride mounts else mounts;
+
+    # We no longer need those when using envfs
+    system.activationScripts.usrbinenv = lib.mkForce "";
+    system.activationScripts.binsh = lib.mkForce "";
+  };
+}