spack setup-env.sh: make zsh loading async compatible, and ~10x faster (in some cases) (#26120)

Currently spack is a bit of a bad actor as a zsh plugin, and it was my
fault.  The autoload and compinit should really be handled by the user,
as was made abundantly clear when I found spack was doing completion
initialization for *all* of my plugins due to a deferred setup that was
getting messed up by it.

Making this conditional took spack load time from 1.5 seconds (with
module loading disabled) to 0.029 seconds. I can actually afford to load
spack by default with this change in.

Hopefully someday we'll do proper zsh completion support, but for now
this helps a lot.

* use zsh hist expansion in place of dirname
* only run (bash)compinit if compdef/complete missing
* add zsh compiled files to .gitignore
* move changes to .in file, because spack

.gitignore

@@ -210,6 +210,9 @@ tramp
 /eshell/history
 /eshell/lastdir
 
+# zsh byte-compiled files
+*.zwc
+
 # elpa packages
 /elpa/
 

share/spack/bash/spack-completion.in

@@ -39,10 +39,14 @@
 
 if test -n "${ZSH_VERSION:-}" ; then
   if [[ "$(emulate)" = zsh ]] ; then
-    # ensure base completion support is enabled, ignore insecure directories
-    autoload -U +X compinit && compinit -i
-    # ensure bash compatible completion support is enabled
-    autoload -U +X bashcompinit && bashcompinit
+    if ! typeset -f compdef >& /dev/null ; then
+        # ensure base completion support is enabled, ignore insecure directories
+        autoload -U +X compinit && compinit -i
+    fi
+    if ! typeset -f complete >& /dev/null ; then
+        # ensure bash compatible completion support is enabled
+        autoload -U +X bashcompinit && bashcompinit
+    fi
     emulate sh -c "source '$0:A'"
     return # stop interpreting file
   fi

share/spack/setup-env.sh

@@ -276,8 +276,13 @@ fi
 #
 # We send cd output to /dev/null to avoid because a lot of users set up
 # their shell so that cd prints things out to the tty.
-_sp_share_dir="$(cd "$(dirname $_sp_source_file)" > /dev/null && pwd)"
-_sp_prefix="$(cd "$(dirname $(dirname $_sp_share_dir))" > /dev/null && pwd)"
+if [ "$_sp_shell" = zsh ]; then
+    _sp_share_dir="${_sp_source_file:A:h}"
+    _sp_prefix="${_sp_share_dir:h:h}"
+else
+    _sp_share_dir="$(cd "$(dirname $_sp_source_file)" > /dev/null && pwd)"
+    _sp_prefix="$(cd "$(dirname $(dirname $_sp_share_dir))" > /dev/null && pwd)"
+fi
 if [ -x "$_sp_prefix/bin/spack" ]; then
     export SPACK_ROOT="${_sp_prefix}"
 else

share/spack/spack-completion.bash

@@ -39,10 +39,14 @@
 
 if test -n "${ZSH_VERSION:-}" ; then
   if [[ "$(emulate)" = zsh ]] ; then
-    # ensure base completion support is enabled, ignore insecure directories
-    autoload -U +X compinit && compinit -i
-    # ensure bash compatible completion support is enabled
-    autoload -U +X bashcompinit && bashcompinit
+    if ! typeset -f compdef >& /dev/null ; then
+        # ensure base completion support is enabled, ignore insecure directories
+        autoload -U +X compinit && compinit -i
+    fi
+    if ! typeset -f complete >& /dev/null ; then
+        # ensure bash compatible completion support is enabled
+        autoload -U +X bashcompinit && bashcompinit
+    fi
     emulate sh -c "source '$0:A'"
     return # stop interpreting file
   fi