home-manager: add zsh completion

Fixes #1075

home-manager/completion.zsh

@@ -0,0 +1,54 @@
+#compdef home-manager
+
+local state ret=1
+
+_arguments \
+  '-A[attribute]:ATTRIBUTE:()' \
+  '-I[search path]:PATH:_files -/' \
+  '-b[backup files]:EXT:()' \
+  '--cores[cores]:NUM:()' \
+  '--keep-failed[keep failed]' \
+  '--keep-going[keep going]' \
+  '(-h --help)'{--help,-h}'[help]' \
+  '(-v --verbose)'{--verbose,-v}'[verbose]' \
+  '(-n --dry-run)'{--dry-run,-n}'[dry run]' \
+  '(-f --file)'{--file,-f}'[configuration file]:FILE:_files' \
+  '(-j --max-jobs)'{--max-jobs,-j}'[max jobs]:NUM:()' \
+  '--option[option]:NAME VALUE:()' \
+  '--show-trace[show trace]' \
+  '1: :->cmds' \
+  '*:: :->args' && ret=0
+
+case "$state" in
+  cmds)
+    _values 'command' \
+      'help[help]' \
+      'edit[edit]' \
+      'build[build]' \
+      'switch[switch]' \
+      'generations[list generations]' \
+      'remove-generations[remove generations]' \
+      'expire-generations[expire generations]' \
+      'packages[managed packages]' \
+      'news[read the news]' \
+      'uninstall[uninstall]' && ret=0
+    ;;
+  args)
+    case $line[1] in
+      remove-generations)
+        _values 'generations' \
+          $(home-manager generations | cut -d ' ' -f 5) && ret=0
+        ;;
+      build|switch)
+        _arguments \
+          '--cores[cores]:NUM:()' \
+          '--keep-failed[keep failed]' \
+          '--keep-going[keep going]' \
+          '--max-jobs[max jobs]:NUM:()' \
+          '--option[option]:NAME VALUE:()' \
+          '--show-trace[show trace]'
+        ;;
+    esac
+esac
+
+return ret

home-manager/default.nix

@@ -37,4 +37,6 @@ runCommand
 
     install -D -m755 ${./completion.bash} \
       $out/share/bash-completion/completions/home-manager
+    install -D -m755 ${./completion.zsh} \
+      $out/share/zsh/site-functions/_home-manager
   ''