perf(tar): cache the parse result of GNU tar help

Author: akinomyoga

completions/tar

@@ -119,6 +119,9 @@ _comp_cmd_gtar__parse_help_line()
     done <<<"$1"
 }
 
+# Cache of _comp_cmd_gtar__parse_help()
+_comp_cmd_gtar__parse_help__mut_cache=
+
 # Parse the output of "tar --help" with GNU tar and store the parse results
 # into variables.
 #
@@ -131,8 +134,18 @@ _comp_cmd_gtar__parse_help_line()
 # @var[out] short_arg_opt
 # @var[out] short_arg_req
 #     The parse results are returned in these variables.
+#
+# @var[in,out] _comp_cmd_gtar__parse_help__mut_cache
+#     The parse results are cached in this global variable.  If this variable
+#     is non-empty, this variable is used to obtain the parse results instead
+#     of parsing the output of "tar --help" again.
 _comp_cmd_gtar__parse_help()
 {
+    if [[ $_comp_cmd_gtar__parse_help__mut_cache ]]; then
+        eval -- "$_comp_cmd_gtar__parse_help__mut_cache"
+        return
+    fi
+
     long_arg_none=""
     long_arg_opt=""
     long_arg_req=""
@@ -168,6 +181,16 @@ _comp_cmd_gtar__parse_help()
         $long_arg_none        $long_arg_opt        $long_arg_req"
 
     short_opts="$short_arg_none$short_arg_opt$short_arg_req"
+
+    printf -v _comp_cmd_gtar__parse_help__mut_cache '%s=%q ' \
+        long_opts "$long_opts" \
+        short_opts "$short_opts" \
+        long_arg_none "$long_arg_none" \
+        long_arg_opt "$long_arg_opt" \
+        long_arg_req "$long_arg_req" \
+        short_arg_none "$short_arg_none" \
+        short_arg_opt "$short_arg_opt" \
+        short_arg_req "$short_arg_req"
 }
 
 # Hack: parse --warning keywords from tar's error output