In workers 50316, I wrote:
> That needs some work to avoid conflicting with other helpers that
> redefine compadd

As far as I can tell that now means only _complete_help and
_approximate, and _approximate already avoids redefining compadd when
it is a function instead of a builtin.  I'm not sure if that affects
the results of _complete_help for contexts that use _approximate.

Nevertheless it seems as though a helper for temporarily redefining
builtins and functions as new functions is possible, so an attempt at
it is attached.  The idea here is to create a new unique function name
and link it to the original function, which preserves the function
body, and then unwind that when the redefined function is not needed.
There's no neat way to do this without help from the caller in the
form of an "always" block.

So after a bit of noodling with that idea, the result is _shadow
(attached as _shadow.txt for list server compatibility).  Example of
usage:

diff --git a/Completion/Base/Widget/_complete_help
b/Completion/Base/Widget/_complete_help
index 69855de9d..da5947e7f 100644
--- a/Completion/Base/Widget/_complete_help
+++ b/Completion/Base/Widget/_complete_help
@@ -10,6 +10,7 @@ _complete_help() {
   local -H _help_filter_funcstack="alternative|call_function|describe|dispatch|wanted|requested|all_labels|next_label"

   {
+    _shadow compadd compcall zstyle
     compadd() { return 1 }
     compcall() { _help_sort_tags use-compctl }
     zstyle() {
@@ -43,7 +44,7 @@ _complete_help() {

     ${1:-_main_complete}
   } always {
-    unfunction compadd compcall zstyle
+    _unshadow compadd compcall zstyle
   }

   for i in "${(@ok)help_funcs}"; do

I'm not certain that Completion/Base/Utility is where _shadow would
best be committed, but currently the only places we might want it are
in completion, so it should be loaded along with completions, so
that's where I was thinking to put it.

Remarks?