Optimize ebuild.sh to cache preprocessing output.

bin/ebuild.sh

 #!/bin/bash
 # Copyright 1999-2011 Gentoo Foundation
 # Distributed under the terms of the GNU General Public License v2
 
 PORTAGE_BIN_PATH="${PORTAGE_BIN_PATH:-/usr/lib/portage/bin}"
 PORTAGE_PYM_PATH="${PORTAGE_PYM_PATH:-/usr/lib/portage/pym}"
 
 if [[ $PORTAGE_SANDBOX_COMPAT_LEVEL -lt 22 ]] ; then
         # Ensure that /dev/std* streams have appropriate sandbox permission for
         # bug #288863. This can be removed after sandbox is fixed and portage
@@ skipping 1808 matching lines @@
 }
 
 # @FUNCTION: preprocess_ebuild_env
 # @DESCRIPTION:
 # Filter any readonly variables from ${T}/environment, source it, and then
 # save it via save_ebuild_env(). This process should be sufficient to prevent
 # any stale variables or functions from an arbitrary environment from
 # interfering with the current environment. This is useful when an existing
 # environment needs to be loaded from a binary or installed package.
 preprocess_ebuild_env() {
-        local _portage_filter_opts=""
-        if [ -f "${T}/environment.raw" ] ; then
-                # This is a signal from the python side, indicating that the
-                # environment may contain stale SANDBOX_{DENY,PREDICT,READ,WRITE}
-                # and FEATURES variables that should be filtered out. Between
-                # phases, these variables are normally preserved.
-                _portage_filter_opts+=" --filter-features --filter-locale --filter-path --filter-sandbox"
-        fi
+        local _portage_filter_opts="--filter-features --filter-locale --filter-path --filter-sandbox"
+
+        # If environment.raw is present, this is a signal from the python side,
+        # indicating that the environment may contain stale FEATURES and
+        # SANDBOX_{DENY,PREDICT,READ,WRITE} variables that should be filtered out.
+        # Otherwise, we don't need to filter the environment.
+        [ -f "${T}/environment.raw" ] || return 0
+
         filter_readonly_variables $_portage_filter_opts < "${T}"/environment \
                 >> "$T/environment.filtered" || return $?
         unset _portage_filter_opts
         mv "${T}"/environment.filtered "${T}"/environment || return $?
         rm -f "${T}/environment.success" || return $?
         # WARNING: Code inside this subshell should avoid making assumptions
         # about variables or functions after source "${T}"/environment has been
         # called. Any variables that need to be relied upon should already be
         # filtered out above.
         (
@@ skipping 508 matching lines @@
                         [[ ! -s $SANDBOX_LOG ]]
                         "$PORTAGE_BIN_PATH"/ebuild-ipc exit $?
                 fi
                 exit 0
         )
         exit $?
 fi
 
 # Do not exit when ebuild.sh is sourced by other scripts.
 true