45424: completion: Add **/sbin to PATH when completing commands like sudo

* Update _command_names to add **/sbin to PATH when not otherwise overridden
  and _comp_priv_prefix is set. This ensures that, on systems where
  unprivileged users don't have **/sbin in their PATHs, we can still complete
  those commands when they try to run them with e.g. sudo

* Update functions for privilege-gaining commands to use the aforementioned
  mechanism

* Fix some other minor issues in _pfexec and _doas

Changes from the posted diff:

* Fix a minor redundancy in _doas

* Add _c_p_p=( '' ) hack to _su

1 files changed, 6 insertions, 0 deletions

diff --git a/Completion/Unix/Command/_su b/Completion/Unix/Command/_su
index 032f867f4..066f5c3b6 100644
--- a/Completion/Unix/Command/_su
+++ b/Completion/Unix/Command/_su
@@ -63,6 +63,12 @@ if (( $words[(i)-] < CURRENT )); then
   norm=2
 fi
 
+# This is set so that _command_names will understand that we're completing for
+# a privileged command, but _call_program won't actually prepend anything to
+# commands if gain-privileges is enabled (which would be undesirable here since
+# su always prompts for a password). We delay setting it until this point so it
+# doesn't cause issues for the check above
+local -a _comp_priv_prefix=( '' )
 _arguments $args ${(e)first} "*:shell arguments:= ->rest" && return
 
 usr=${${(Q)line[norm]}/--/root}