nixos/core: use nix-index

and check for file existence before using path

nix-os/core.nix

@@ -79,6 +79,13 @@ in
     rerere.enabled = true;
   };
 
+  # Use nix-index for command-not-found handler
+  programs.command-not-found.enable = false;
+  programs.nix-index = {
+    enable = true;
+    enableBashIntegration = true;
+  };
+
   # Enable fail2ban because of the OpenSSH server
   services.fail2ban = {
     enable = true;

outputs.nix

@@ -45,7 +45,7 @@ self = {
             {
               config.nixpkgs.overlays = [
                 ( import ./pkgs/overlays/selfExpr.nix { nixpkgsPath = "${self}/pkgs/top-level/impure.nix"; } )
-                ( import "${inputs.nixpkgs}/pkgs/top-level/by-name-overlay.nix" "${self}/pkgs/by-name" )
+                ( import ./pkgs/top-level/by-name-overlay.nix "${self}/pkgs/by-name" )
                 self.overlays.versionInfoFixup
               ];
             }

pkgs/by-name/ni/nix-index/cnfOutput.patch

@@ -0,0 +1,66 @@
+diff --git a/command-not-found.sh b/command-not-found.sh
+index 5f30bad..3854297 100755
+--- a/command-not-found.sh
++++ b/command-not-found.sh
+@@ -73,51 +73,30 @@ EOF
+             else
+                 if [ -e "$HOME/.nix-profile/manifest.json" ]; then
+                     >&2 cat <<EOF
+-The program '$cmd' is currently not installed. You can install it
+-by typing:
+-  nix profile install $toplevel#$attrs
+-
+-Or run it once with:
+-  nix shell $toplevel#$attrs -c $cmd ...
++The program '$cmd' is not in your PATH. You can make it available in an
++ephemeral shell by typing:
++  nix shell $toplevel#$attrs
+ EOF
+                 else
+                     >&2 cat <<EOF
+-The program '$cmd' is currently not installed. You can install it
+-by typing:
+-  nix-env -iA $toplevel.$attrs
+-
+-Or run it once with:
+-  nix-shell -p $attrs --run '$cmd ...'
++The program '$cmd' is not in your PATH. You can make it available in an
++ephemeral shell by typing:
++  nix-shell -p $attrs
+ EOF
+                 fi
+             fi
+             ;;
+         *)
+             >&2 cat <<EOF
+-The program '$cmd' is currently not installed. It is provided by
+-several packages. You can install it by typing one of the following:
+-EOF
+-
+-            # ensure we get each element of attrs
+-            # in a cross platform way
+-            while read attr; do
+-                if [ -e "$HOME/.nix-profile/manifest.json" ]; then
+-                    >&2 echo "  nix profile install $toplevel#$attr"
+-                else
+-                    >&2 echo "  nix-env -iA $toplevel.$attr"
+-                fi
+-            done <<< "$attrs"
+-
+-            >&2 cat <<EOF
+-
+-Or run it once with:
++The program '$cmd' is not in your PATH. You can make it available in an
++ephemeral shell by typing:
+ EOF
+ 
+             while read attr; do
+                 if [ -e "$HOME/.nix-profile/manifest.json" ]; then
+-                    >&2 echo "  nix shell $toplevel#$attr -c $cmd ..."
++                    >&2 echo "  nix shell $toplevel#$attr"
+                 else
+-                    >&2 echo "  nix-shell -p $attr --run '$cmd ...'"
++                    >&2 echo "  nix-shell -p $attr"
+                 fi
+             done <<< "$attrs"
+             ;;

pkgs/by-name/ni/nix-index/override.nix

@@ -0,0 +1,9 @@
+{self, super, package }:
+
+package.override {
+  nix-index-unwrapped = self.nix-index-unwrapped.overrideAttrs (oldAttrs: {
+    patches = oldAttrs.patches or [] ++ [
+      ./cnfOutput.patch
+    ];
+  });
+}

pkgs/top-level/by-name-overlay.nix

@@ -0,0 +1,50 @@
+# Modified copy of github:NixOS/nixpkgs pkgs/top-level/by-name-overlay.nix
+# as of commit c0d0be00d4ecc4b51d2d6948e37466194c1e6c51
+
+# This file turns the pkgs/by-name directory into an overlay that adds all the defined packages.
+# No validity checks are done here.
+
+# Type: Path -> Overlay
+baseDirectory:
+let
+  lib = (import ../../outputs.nix {}).lib;
+
+  inherit (builtins)
+    readDir
+    ;
+
+  inherit (lib.attrsets)
+    mapAttrs
+    mapAttrsToList
+    mergeAttrsList
+    ;
+
+  # Package files for a single shard
+  # Type: String -> String -> String -> AttrsOf Path
+  namesForShard = nixFilename: shard: type:
+    if type != "directory" then
+      # Ignore all non-directories.
+      { }
+    else
+      mapAttrs
+        (name: _: baseDirectory + "/${shard}/${name}/${nixFilename}")
+        (readDir (baseDirectory + "/${shard}"));
+
+  # The attribute set mapping names to the package files defining them
+  # Type: String -> AttrsOf Path
+  packageFiles = nixFilename: lib.pipe baseDirectory [
+    readDir
+    (mapAttrsToList (namesForShard nixFilename))
+    mergeAttrsList
+    # Filter out paths that don't have a ${nixFilename} file
+    (lib.filterAttrs (_: lib.pathExists))
+  ];
+in
+self: super:
+mapAttrs (name: file:
+  self.callPackage file { inherit self super; package = super.${name}; }
+) (packageFiles "override.nix")
+// mapAttrs (name: file:
+  self.callPackage file { }
+) (packageFiles "package.nix")
+

pkgs/top-level/default.nix

@@ -16,7 +16,7 @@ let
       ( import ../overlays/selfExpr.nix { nixpkgsPath = "${builtins.toString ../..}/pkgs/top-level/impure.nix"; } )
       ( import ../overlays/unstable.nix )
       ( import ../overlays/version-info-fixup.nix { inherit inputs; } )
-      ( import "${inputs.nixpkgs}/pkgs/top-level/by-name-overlay.nix" ../by-name )
+      ( import ./by-name-overlay.nix ../by-name )
     ];
   };
 in