add completion for 'cache' subcommand

assets/completions/bat.zsh

@@ -1,9 +1,27 @@
 #compdef bat
-# FIXME: help me with the subcommand `cache`, zsh completion is hard as hell
 
+local context state state_descr line
+typeset -A opt_args
+
+(( $+functions[_cache_subcommand] )) ||
+_cache_subcommand() {
     local -a args
-local state
+    args=(
+        '(-b --build -c --clear)'{-b,--build}'[Initialize or update the syntax/theme cache]'
+        '(-b --build -c --clear)'{-c,--clear}'[Remove the cached syntax definitions and themes]'
+        '(--source)'--source='[Use a different directory to load syntaxes and themes from]:directory:_files -/'
+        '(--target)'--target='[Use a different directory to store the cached syntax and theme set]:directory:_files -/'
+        '(--blank)'--blank'[Create completely new syntax and theme sets)]'
+        '(: -)'{-h,--help}'[Prints help information]'
+        '*: :'
+    )
 
+    _arguments -S -s $args
+}
+
+(( $+functions[_bat_main] )) ||
+_bat_main() {
+    local -a args
     args=(
         '(-A --show-all)'{-A,--show-all}'[Show non-printable characters (space, tab, newline, ..)]'
         {-p,--plain}'[Show plain style (alias for `--style=plain`)]:When `-p` is used twice (`-pp`), it also disables automatic paging (alias for `--style=plain --paging=never`)'
@@ -54,3 +72,20 @@ case "$state" in
             _values -s , 'style' auto full plain changes header grid numbers snip
         ;;
     esac
+}
+
+# first positional argument
+if (( ${#words} == 2 )); then
+    _values subcommand cache
+    _bat_main
+else
+    case $words[2] in
+        cache)
+            _cache_subcommand
+        ;;
+
+        *)
+            _bat_main
+        ;;
+    esac
+fi