command-not-found: disable by default, simplify, document (#416425)

doc/release-notes/rl-2511.section.md

@@ -18,6 +18,7 @@
 - `base16-builder` node package has been removed due to lack of upstream maintenance.
 - `gentium` package now provides `Gentium-*.ttf` files, and not `GentiumPlus-*.ttf` files like before. The font identifiers `Gentium Plus*` are available in the `gentium-plus` package, and if you want to use the more recently updated package `gentium` [by sil](https://software.sil.org/gentium/), you should update your configuration files to use the `Gentium` font identifier.
 - `space-orbit` package has been removed due to lack of upstream maintenance. Debian upstream stopped tracking it in 2011.
+- `command-not-found` package is now disabled by default; it works only for nix-channels based systems, and requires setup for it to work.
 
 - `gnome-keyring` no longer ships with an SSH agent anymore because it has been deprecated upstream. You should use `gcr_4` instead, which provides the same features. More information on why this was done can be found on [the relevant GCR upstream PR](https://gitlab.gnome.org/GNOME/gcr/-/merge_requests/67).
 

nixos/modules/programs/command-not-found/command-not-found.nix

@@ -33,10 +33,16 @@ in
 
     enable = lib.mkOption {
       type = lib.types.bool;
-      default = true;
+      default = false;
       description = ''
         Whether interactive shells should show which Nix package (if
         any) provides a missing command.
+
+        Requires nix-channels to be set and downloaded (sudo nix-channels --update.)
+
+        See also nix-index and nix-index-database as an alternative for flakes-based systems.
+
+        Additionally, having the env var NIX_AUTO_RUN set will automatically run the matching package, and with NIX_AUTO_RUN_INTERACTIVE it will confirm the package before running.
       '';
     };
 
@@ -54,47 +60,24 @@ in
 
   config = lib.mkIf cfg.enable {
     programs.bash.interactiveShellInit = ''
-      # This function is called whenever a command is not found.
       command_not_found_handle() {
-        local p='${commandNotFound}/bin/command-not-found'
-        if [ -x "$p" ] && [ -f '${cfg.dbPath}' ]; then
-          # Run the helper program.
-          "$p" "$@"
-          # Retry the command if we just installed it.
-          if [ $? = 126 ]; then
-            "$@"
-          else
-            return 127
-          fi
-        else
-          echo "$1: command not found" >&2
-          return 127
-        fi
+        '${commandNotFound}/bin/command-not-found' "$@"
       }
     '';
 
     programs.zsh.interactiveShellInit = ''
-      # This function is called whenever a command is not found.
       command_not_found_handler() {
-        local p='${commandNotFound}/bin/command-not-found'
-        if [ -x "$p" ] && [ -f '${cfg.dbPath}' ]; then
-          # Run the helper program.
-          "$p" "$@"
-
-          # Retry the command if we just installed it.
-          if [ $? = 126 ]; then
-            "$@"
-          else
-            return 127
-          fi
-        else
-          # Indicate than there was an error so ZSH falls back to its default handler
-          echo "$1: command not found" >&2
-          return 127
-        fi
+        '${commandNotFound}/bin/command-not-found' "$@"
       }
     '';
 
+    # NOTE: Fish by itself checks for nixos command-not-found, let's instead makes it explicit.
+    programs.fish.interactiveShellInit = ''
+      function fish_command_not_found
+         "${commandNotFound}/bin/command-not-found" $argv
+      end
+    '';
+
     environment.systemPackages = [ commandNotFound ];
   };
 

nixos/modules/programs/command-not-found/command-not-found.pl

@@ -10,6 +10,24 @@ my $program = $ARGV[0];
 
 my $dbPath = "@dbPath@";
 
+if (! -e $dbPath) {
+    print STDERR "$program: command not found\n";
+    print STDERR "\n";
+    print STDERR "command-not-found: Missing package database\n";
+    print STDERR "command-not-found is a tool for searching for missing packages.\n";
+    print STDERR "No database was found, this likely means the database hasn't been generated yet.\n";
+    print STDERR "This tool requires nix-channels to generate the database for the `nixos` channel.\n";
+    print STDERR "\n";
+    print STDERR "If you are using nix-channels you can run:\n";
+    print STDERR "    sudo nix-channels --update\n";
+    print STDERR "\n";
+    print STDERR "If you are using flakes, see nix-index and nix-index-database.\n";
+    print STDERR "\n";
+    print STDERR "If you would like to disable this message you can set:\n";
+    print STDERR "    programs.command-not-found.enable = false;\n";
+    exit 127;
+}
+
 my $dbh = DBI->connect("dbi:SQLite:dbname=$dbPath", "", "")
     or die "cannot open database `$dbPath'";
 $dbh->{RaiseError} = 0;