setup-env: allow users to skip module function setup (#24236)

* setup-env: allow users to skip module function setup

* Add documentation on SPACK_SKIP_MODULES

lib/spack/docs/getting_started.rst

@@ -70,7 +70,13 @@ Sourcing these files will put the ``spack`` command in your ``PATH``, set
 up your ``MODULEPATH`` to use Spack's packages, and add other useful
 shell integration for :ref:`certain commands <packaging-shell-support>`,
 :ref:`environments <environments>`, and :ref:`modules <modules>`. For
-``bash``, it also sets up tab completion.
+``bash`` and ``zsh``, it also sets up tab completion.
+
+In order to know which directory to add to your ``MODULEPATH``, these scripts
+query the ``spack`` command. On shared filesystems, this can be a bit slow,
+especially if you log in frequently. If you don't use modules, or want to set
+``MODULEPATH`` manually instead, you can set the ``SPACK_SKIP_MODULES``
+environment variable to skip this step and speed up sourcing the file.
 
 If you do not want to use Spack's shell support, you can always just run
 the ``spack`` command directly from ``spack/bin/spack``.

share/spack/setup-env.fish

@@ -703,7 +703,7 @@ set -xg _sp_shell "fish"
 # Check whether we need environment-variables (module) <= `use` is not available
 #
 set -l need_module "no"
-if not functions -q use; and not functions -q module
+if test -z "$SPACK_SKIP_MODULES"; and not functions -q use; and not functions -q module
     set need_module "yes"
 end
 

share/spack/setup-env.sh

@@ -307,7 +307,7 @@ _spack_fn_exists() {
 }
 
 need_module="no"
-if ! _spack_fn_exists use && ! _spack_fn_exists module; then
+if [ -z "${SPACK_SKIP_MODULES+x}" ] && ! _spack_fn_exists use && ! _spack_fn_exists module; then
     need_module="yes"
 fi;