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

1 files changed, 7 insertions, 2 deletions

diff --git a/share/spack/setup-env.sh b/share/spack/setup-env.sh
index 8936f6ca0d..21bd696386 100755
--- a/share/spack/setup-env.sh
+++ b/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