nixos-rebuild: Locally own the nixos-rebuild completion

pkgs/os-specific/linux/nixos-rebuild/_nixos-rebuild

@@ -0,0 +1,165 @@
+#!/usr/bin/env bash
+
+# We're faking a `nix build` command-line to re-use Nix's own completion
+# for the few options passed through to Nix.
+_nixos-rebuild_pretend-nix() {
+  COMP_LINE="nix build ${COMP_LINE}"
+  # number of prepended chars
+  (( COMP_POINT = COMP_POINT + 10))
+
+  COMP_WORDS=(
+    nix build
+    "${COMP_WORDS[@]}"
+  )
+  # Add the amount of prepended words
+  (( COMP_CWORD = COMP_CWORD + 2))
+  _complete_nix "nix"
+}
+
+_nixos-rebuild() {
+  local curr="$2"
+  local prev="$3"
+  local subcommandGiven=0
+  local word
+  local subcommand
+
+  __load_completion nix
+
+  # Arrays are re-ordered by the completion, so it's fine to sort them in logical chunks
+  local all_args=(
+    --verbose -v
+
+    # nixos-rebuild options
+    --fast
+    --no-build-nix
+    --profile-name -p # name
+    --rollback
+    --specialisation -c # name
+    --use-remote-sudo
+    --build-host # host
+    --target-host # host
+    # Used with list-generations
+    --json
+
+    # generation switching options
+    --install-bootloader
+
+    # nix-channel options
+    --upgrade
+    --upgrade-all
+
+    # flakes options
+    --commit-lock-file
+    --flake # flake-uri
+    --override-input # input-name flake-uri
+    --recreate-lock-file
+    --update-input
+    --no-flake
+    --no-registries
+    --no-update-lock-file
+    --no-write-lock-file
+
+    # Nix-copy options
+    --use-substitutes --substitute-on-destination -s
+
+    # Nix options
+    --option
+    --impure
+    --builders # builder-spec
+    --show-trace
+    --keep-failed -K
+    --keep-going -k
+    --max-jobs -j # number
+    --log-format # format
+    -I # NIX_PATH
+  )
+
+  local all_subcommands=(
+    boot
+    build
+    build-vm
+    build-vm-with-bootloader
+    dry-activate
+    dry-build
+    edit
+    list-generations
+    switch
+    test
+  )
+
+  # Suggest arguments that can be consumed under some conditions only
+  for word in "${COMP_WORDS[@]}"; do
+    for subcommand in "${all_subcommands[@]}"; do
+      if [[ "$word" == "$subcommand" ]]; then
+        subcommandGiven=1
+      fi
+    done
+  done
+
+  # Fake out a way to complete the second arg to some options
+  case "${COMP_WORDS[COMP_CWORD-2]}" in
+    "--override-input")
+      prev="--override-input_2"
+      ;;
+    "--option")
+      prev="--option_2"
+      ;;
+  esac
+
+  case "$prev" in
+    --max-jobs|-j)
+      COMPREPLY=( )
+      ;;
+
+    --profile-name|-p)
+      if [[ "$curr" == "" ]]; then
+        COMPREPLY=( /nix/var/nix/profiles/* )
+      else
+        COMPREPLY=( "$curr"* )
+      fi
+      ;;
+
+    --build-host|--target-host|-t|-h)
+      _known_hosts_real "$curr"
+    ;;
+
+    --specialisation|-c)
+      COMPREPLY=()
+      ;;
+
+    -I)
+      _nixos-rebuild_pretend-nix
+      ;;
+    --builders)
+      _nixos-rebuild_pretend-nix
+      ;;
+    --flake)
+      _nixos-rebuild_pretend-nix
+      ;;
+    --override-input)
+      _nixos-rebuild_pretend-nix
+      ;;
+    --override-input_2)
+      _nixos-rebuild_pretend-nix
+      ;;
+    --log-format)
+      _nixos-rebuild_pretend-nix
+      ;;
+    --option)
+      _nixos-rebuild_pretend-nix
+      ;;
+    --option_2)
+      _nixos-rebuild_pretend-nix
+      ;;
+
+    *)
+      if [[ "$curr" == -* ]] || (( subcommandGiven )); then
+        COMPREPLY=( $(compgen -W "${all_args[*]}" -- "$2") )
+      else
+        COMPREPLY=( $(compgen -W "${all_subcommands[*]}" -- "$2") )
+      fi
+    ;;
+  esac
+}
+
+complete -F _nixos-rebuild nixos-rebuild

pkgs/os-specific/linux/nixos-rebuild/default.nix

@@ -28,6 +28,9 @@ substituteAll {
   ];
   postInstall = ''
     installManPage ${./nixos-rebuild.8}
+
+    installShellCompletion \
+      --bash ${./_nixos-rebuild}
   '';
 
   # run some a simple installer tests to make sure nixos-rebuild still works for them