fix(_command_offset): receive index in COMP_WORDS through compat name

bash_completion

@@ -2390,14 +2390,33 @@ _comp_command_offset()
         done
     fi
 }
-_comp_deprecate_func _command_offset _comp_command_offset
+
+# @deprecated Use "_comp_command_offset" instead.  It should be noted that the
+# new interface "_comp_command_offset" is changed to receive an index in
+# "words" instead of that in "COMP_WORDS" as "_command_offset" did.
+_command_offset()
+{
+    # This compatibility function assumes the first argument to be the index in
+    # "COMP_WORDS" instead of that in "words".  To tell it to the new interface
+    # "_comp_command_offset", we locally make the variable "words" in the unset
+    # state.
+    local words
+    unset -v words
+    _comp_command_offset "$@"
+}
 
 # A _comp_command_offset wrapper function for use when the offset is unknown.
 # Only intended to be used as a completion function directly associated
 # with a command, not to be invoked from within other completion functions.
 #
 _comp_command()
 {
+    # We locally make the shell variable "words" in the unset state to tell
+    # "_comp_command_offset" that the index is intended to be that in
+    # "COMP_WORDS" instead of "words".
+    local words
+    unset -v words
+
     local offset i
 
     # find actual offset, as position of the first non-option