Merge pull request #28057 from obsidiansystems/stdenv-set-u

stdenv-setup: use `set -u`
This commit is contained in:
John Ericson 2017-08-25 11:19:58 -04:00 committed by GitHub
commit 2e7a390212

View file

@ -1,4 +1,4 @@
set -e
set -eu
set -o pipefail
: ${outputs:=out}
@ -13,16 +13,22 @@ set -o pipefail
# code). The hooks for <hookName> are the shell function or variable
# <hookName>, and the values of the shell array <hookName>Hooks.
runHook() {
local oldOpts="$(shopt -po nounset)"
set -u # May be called from elsewhere, so do `set -u`.
local hookName="$1"
shift
local var="$hookName"
if [[ "$hookName" =~ Hook$ ]]; then var+=s; else var+=Hooks; fi
local hooksSlice="${hookName%Hook}Hooks[@]"
local varRef="$var[@]"
local hook
for hook in "_callImplicitHook 0 $hookName" "${!varRef}"; do
# Hack around old bash being bad and thinking empty arrays are
# undefined.
for hook in "_callImplicitHook 0 $hookName" ${!hooksSlice+"${!hooksSlice}"}; do
_eval "$hook" "$@"
set -u # To balance `_eval`
done
eval "${oldOpts}"
return 0
}
@ -30,19 +36,25 @@ runHook() {
# Run all hooks with the specified name, until one succeeds (returns a
# zero exit code). If none succeed, return a non-zero exit code.
runOneHook() {
local oldOpts="$(shopt -po nounset)"
set -u # May be called from elsewhere, so do `set -u`.
local hookName="$1"
shift
local var="$hookName"
if [[ "$hookName" =~ Hook$ ]]; then var+=s; else var+=Hooks; fi
local hooksSlice="${hookName%Hook}Hooks[@]"
local varRef="$var[@]"
local hook
for hook in "_callImplicitHook 1 $hookName" "${!varRef}"; do
local hook ret=1
# Hack around old bash like above
for hook in "_callImplicitHook 1 $hookName" ${!hooksSlice+"${!hooksSlice}"}; do
if _eval "$hook" "$@"; then
return 0
ret=0
break
fi
set -u # To balance `_eval`
done
return 1
eval "${oldOpts}"
return "$ret"
}
@ -52,27 +64,42 @@ runOneHook() {
# environment variables) and from shell scripts (as functions). If you
# want to allow multiple hooks, use runHook instead.
_callImplicitHook() {
set -u
local def="$1"
local hookName="$2"
case "$(type -t "$hookName")" in
(function|alias|builtin) "$hookName";;
(file) source "$hookName";;
(function|alias|builtin)
set +u
"$hookName";;
(file)
set +u
source "$hookName";;
(keyword) :;;
(*) if [ -z "${!hookName}" ]; then return "$def"; else eval "${!hookName}"; fi;;
(*) if [ -z "${!hookName:-}" ]; then
return "$def";
else
set +u
eval "${!hookName}"
fi;;
esac
# `_eval` expects hook to need nounset disable and leave it
# disabled anyways, so Ok to to delegate. The alternative of a
# return trap is no good because it would affect nested returns.
}
# A function wrapper around eval that ensures that return inside
# hooks exits the hook, not the caller.
# hooks exits the hook, not the caller. Also will only pass args if
# command can take them
_eval() {
local code="$1"
shift
if [ "$(type -t "$code")" = function ]; then
eval "$code \"\$@\""
if [ "$(type -t "$1")" = function ]; then
set +u
"$@" # including args
else
eval "$code"
set +u
eval "$1"
fi
# `run*Hook` reenables `set -u`
}
@ -103,7 +130,7 @@ exitHandler() {
exitCode="$?"
set +e
if [ -n "$showBuildStats" ]; then
if [ -n "${showBuildStats:-}" ]; then
times > "$NIX_BUILD_TOP/.times"
local -a times=($(cat "$NIX_BUILD_TOP/.times"))
# Print the following statistics:
@ -114,14 +141,14 @@ exitHandler() {
echo "build time elapsed: " "${times[@]}"
fi
if [ "$exitCode" != 0 ]; then
if (( "$exitCode" != 0 )); then
runHook failureHook
# If the builder had a non-zero exit code and
# $succeedOnFailure is set, create the file
# $out/nix-support/failed to signal failure, and exit
# normally. Otherwise, return the original exit code.
if [ -n "$succeedOnFailure" ]; then
if [ -n "${succeedOnFailure:-}" ]; then
echo "build failed with exit code $exitCode (ignored)"
mkdir -p "$out/nix-support"
printf "%s" "$exitCode" > "$out/nix-support/failed"
@ -147,7 +174,7 @@ addToSearchPathWithCustomDelimiter() {
local varName="$2"
local dir="$3"
if [ -d "$dir" ]; then
export "${varName}=${!varName}${!varName:+$delimiter}${dir}"
export "${varName}=${!varName:+${!varName}${delimiter}}${dir}"
fi
}
@ -171,12 +198,12 @@ ensureDir() {
# The function is used in multiple-outputs.sh hook,
# so it is defined here but tried after the hook.
_addRpathPrefix() {
if [ "$NIX_NO_SELF_RPATH" != 1 ]; then
if [ "${NIX_NO_SELF_RPATH:-0}" != 1 ]; then
export NIX_LDFLAGS="-rpath $1/lib $NIX_LDFLAGS"
if [ -n "$NIX_LIB64_IN_SELF_RPATH" ]; then
if [ -n "${NIX_LIB64_IN_SELF_RPATH:-}" ]; then
export NIX_LDFLAGS="-rpath $1/lib64 $NIX_LDFLAGS"
fi
if [ -n "$NIX_LIB32_IN_SELF_RPATH" ]; then
if [ -n "${NIX_LIB32_IN_SELF_RPATH:-}" ]; then
export NIX_LDFLAGS="-rpath $1/lib32 $NIX_LDFLAGS"
fi
fi
@ -242,13 +269,13 @@ for i in $initialPath; do
addToSearchPath PATH "$i/bin"
done
if [ "$NIX_DEBUG" = 1 ]; then
if [ "${NIX_DEBUG:-}" = 1 ]; then
echo "initial path: $PATH"
fi
# Check that the pre-hook initialised SHELL.
if [ -z "$SHELL" ]; then echo "SHELL not set"; exit 1; fi
if [ -z "${SHELL:-}" ]; then echo "SHELL not set"; exit 1; fi
BASH="$SHELL"
export CONFIG_SHELL="$SHELL"
@ -259,7 +286,7 @@ paxmark() { true; }
# Execute the pre-hook.
if [ -z "$shell" ]; then export shell="$SHELL"; fi
if [ -z "${shell:-}" ]; then export shell="$SHELL"; fi
runHook preHook
@ -279,11 +306,12 @@ findInputs() {
# nix-shell doesn't use impure bash. This should replace the O(n)
# case with an O(1) hash map lookup, assuming bash is implemented
# well :D.
local varRef="$var[*]"
case "${!varRef}" in
local varSlice="$var[*]"
# ${..-} to hack around old bash empty array problem
case "${!varSlice-}" in
*" $pkg "*) return 0 ;;
esac
unset -v varSlice
eval "$var"'+=("$pkg")'
@ -293,7 +321,10 @@ findInputs() {
fi
if [ -f "$pkg" ]; then
local oldOpts="$(shopt -po nounset)"
set +u
source "$pkg"
eval "$oldOpts"
fi
if [ -d "$pkg/bin" ]; then
@ -301,7 +332,10 @@ findInputs() {
fi
if [ -f "$pkg/nix-support/setup-hook" ]; then
local oldOpts="$(shopt -po nounset)"
set +u
source "$pkg/nix-support/setup-hook"
eval "$oldOpts"
fi
if [ -f "$pkg/nix-support/$propagatedBuildInputsFile" ]; then
@ -312,23 +346,22 @@ findInputs() {
fi
}
if [ -z "$crossConfig" ]; then
declare -a nativePkgs crossPkgs
if [ -z "${crossConfig:-}" ]; then
# Not cross-compiling - both buildInputs (and variants like propagatedBuildInputs)
# are handled identically to nativeBuildInputs
declare -a nativePkgs
for i in $nativeBuildInputs $buildInputs \
$defaultNativeBuildInputs $defaultBuildInputs \
$propagatedNativeBuildInputs $propagatedBuildInputs; do
for i in ${nativeBuildInputs:-} ${buildInputs:-} \
${defaultNativeBuildInputs:-} ${defaultBuildInputs:-} \
${propagatedNativeBuildInputs:-} ${propagatedBuildInputs:-}; do
findInputs "$i" nativePkgs propagated-native-build-inputs
done
else
declare -a crossPkgs
for i in $buildInputs $defaultBuildInputs $propagatedBuildInputs; do
for i in ${buildInputs:-} ${defaultBuildInputs:-} ${propagatedBuildInputs:-}; do
findInputs "$i" crossPkgs propagated-build-inputs
done
declare -a nativePkgs
for i in $nativeBuildInputs $defaultNativeBuildInputs $propagatedNativeBuildInputs; do
for i in ${nativeBuildInputs:-} ${defaultNativeBuildInputs:-} ${propagatedNativeBuildInputs:-}; do
findInputs "$i" nativePkgs propagated-native-build-inputs
done
fi
@ -355,7 +388,8 @@ _addToNativeEnv() {
runHook envHook "$pkg"
}
for i in "${nativePkgs[@]}"; do
# Old bash empty array hack
for i in ${nativePkgs+"${nativePkgs[@]}"}; do
_addToNativeEnv "$i"
done
@ -367,7 +401,8 @@ _addToCrossEnv() {
runHook crossEnvHook "$pkg"
}
for i in "${crossPkgs[@]}"; do
# Old bash empty array hack
for i in ${crossPkgs+"${crossPkgs[@]}"}; do
_addToCrossEnv "$i"
done
@ -384,17 +419,17 @@ export TZ=UTC
# Set the prefix. This is generally $out, but it can be overriden,
# for instance if we just want to perform a test build/install to a
# temporary location and write a build report to $out.
if [ -z "$prefix" ]; then
if [ -z "${prefix:-}" ]; then
prefix="$out";
fi
if [ "$useTempPrefix" = 1 ]; then
if [ "${useTempPrefix:-}" = 1 ]; then
prefix="$NIX_BUILD_TOP/tmp_prefix";
fi
PATH=$_PATH${_PATH:+:}$PATH
if [ "$NIX_DEBUG" = 1 ]; then
PATH="${_PATH-}${_PATH:+${PATH:+:}}$PATH"
if [ "${NIX_DEBUG:-}" = 1 ]; then
echo "final path: $PATH"
fi
@ -423,7 +458,7 @@ export NIX_BUILD_CORES
# Prevent OpenSSL-based applications from using certificates in
# /etc/ssl.
# Leave it in shells for convenience.
if [ -z "$SSL_CERT_FILE" ] && [ -z "$IN_NIX_SHELL" ]; then
if [ -z "${SSL_CERT_FILE:-}" ] && [ -z "${IN_NIX_SHELL:-}" ]; then
export SSL_CERT_FILE=/no-cert-file.crt
fi
@ -508,7 +543,7 @@ substituteAll() {
# Select all environment variables that start with a lowercase character.
for varName in $(env | sed -e $'s/^\([a-z][^= \t]*\)=.*/\\1/; t \n d'); do
if [ "$NIX_DEBUG" = "1" ]; then
if [ "${NIX_DEBUG:-}" = "1" ]; then
echo "@${varName}@ -> '${!varName}'"
fi
args+=("--subst-var" "$varName")
@ -535,7 +570,7 @@ substituteAllInPlace() {
# then go to the build directory and source in `env-vars' to reproduce
# the environment used for building.
dumpVars() {
if [ "$noDumpEnvVars" != 1 ]; then
if [ "${noDumpEnvVars:-0}" != 1 ]; then
export > "$NIX_BUILD_TOP/env-vars" || true
fi
}
@ -600,8 +635,8 @@ unpackFile() {
unpackPhase() {
runHook preUnpack
if [ -z "$srcs" ]; then
if [ -z "$src" ]; then
if [ -z "${srcs:-}" ]; then
if [ -z "${src:-}" ]; then
# shellcheck disable=SC2016
echo 'variable $src or $srcs should point to the source'
exit 1
@ -626,10 +661,13 @@ unpackPhase() {
done
# Find the source directory.
if [ -n "$setSourceRoot" ]; then
# set to empty if unset
: ${sourceRoot=}
if [ -n "${setSourceRoot:-}" ]; then
runOneHook setSourceRoot
elif [ -z "$sourceRoot" ]; then
sourceRoot=
for i in *; do
if [ -d "$i" ]; then
case $dirsBefore in
@ -657,7 +695,7 @@ unpackPhase() {
# By default, add write permission to the sources. This is often
# necessary when sources have been copied from other store
# locations.
if [ "$dontMakeSourcesWritable" != 1 ]; then
if [ "${dontMakeSourcesWritable:-0}" != 1 ]; then
chmod -R u+w "$sourceRoot"
fi
@ -668,7 +706,7 @@ unpackPhase() {
patchPhase() {
runHook prePatch
for i in $patches; do
for i in ${patches:-}; do
header "applying patch $i" 3
local uncompress=cat
case "$i" in
@ -702,11 +740,15 @@ fixLibtool() {
configurePhase() {
runHook preConfigure
# set to empty if unset
: ${configureScript=}
: ${configureFlags=}
if [[ -z "$configureScript" && -x ./configure ]]; then
configureScript=./configure
fi
if [ -z "$dontFixLibtool" ]; then
if [ -z "${dontFixLibtool:-}" ]; then
local i
find . -iname "ltmain.sh" -print0 | while IFS='' read -r -d '' i; do
echo "fixing libtool script $i"
@ -714,27 +756,30 @@ configurePhase() {
done
fi
if [[ -z "$dontAddPrefix" && -n "$prefix" ]]; then
if [[ -z "${dontAddPrefix:-}" && -n "$prefix" ]]; then
configureFlags="${prefixKey:---prefix=}$prefix $configureFlags"
fi
# Add --disable-dependency-tracking to speed up some builds.
if [ -z "$dontAddDisableDepTrack" ]; then
if [ -z "${dontAddDisableDepTrack:-}" ]; then
if [ -f "$configureScript" ] && grep -q dependency-tracking "$configureScript"; then
configureFlags="--disable-dependency-tracking $configureFlags"
fi
fi
# By default, disable static builds.
if [ -z "$dontDisableStatic" ]; then
if [ -z "${dontDisableStatic:-}" ]; then
if [ -f "$configureScript" ] && grep -q enable-static "$configureScript"; then
configureFlags="--disable-static $configureFlags"
fi
fi
if [ -n "$configureScript" ]; then
# Old bash empty array hack
# shellcheck disable=SC2086
local flagsArray=($configureFlags "${configureFlagsArray[@]}")
local flagsArray=(
$configureFlags ${configureFlagsArray+"${configureFlagsArray[@]}"}
)
echoCmd 'configure flags' "${flagsArray[@]}"
# shellcheck disable=SC2086
$configureScript "${flagsArray[@]}"
@ -750,17 +795,22 @@ configurePhase() {
buildPhase() {
runHook preBuild
if [[ -z "$makeFlags" && ! ( -n "$makefile" || -e Makefile || -e makefile || -e GNUmakefile ) ]]; then
# set to empty if unset
: ${makeFlags=}
if [[ -z "$makeFlags" && ! ( -n "${makefile:-}" || -e Makefile || -e makefile || -e GNUmakefile ) ]]; then
echo "no Makefile, doing nothing"
else
# See https://github.com/NixOS/nixpkgs/pull/1354#issuecomment-31260409
makeFlags="SHELL=$SHELL $makeFlags"
# Old bash empty array hack
# shellcheck disable=SC2086
local flagsArray=( \
${enableParallelBuilding:+-j${NIX_BUILD_CORES} -l${NIX_BUILD_CORES}} \
$makeFlags "${makeFlagsArray[@]}" \
$buildFlags "${buildFlagsArray[@]}")
local flagsArray=(
${enableParallelBuilding:+-j${NIX_BUILD_CORES} -l${NIX_BUILD_CORES}}
$makeFlags ${makeFlagsArray+"${makeFlagsArray[@]}"}
$buildFlags ${buildFlagsArray+"${buildFlagsArray[@]}"}
)
echoCmd 'build flags' "${flagsArray[@]}"
make ${makefile:+-f $makefile} "${flagsArray[@]}"
@ -774,11 +824,14 @@ buildPhase() {
checkPhase() {
runHook preCheck
# Old bash empty array hack
# shellcheck disable=SC2086
local flagsArray=( \
${enableParallelBuilding:+-j${NIX_BUILD_CORES} -l${NIX_BUILD_CORES}} \
$makeFlags "${makeFlagsArray[@]}" \
${checkFlags:-VERBOSE=y} "${checkFlagsArray[@]}" ${checkTarget:-check})
local flagsArray=(
${enableParallelBuilding:+-j${NIX_BUILD_CORES} -l${NIX_BUILD_CORES}}
$makeFlags ${makeFlagsArray+"${makeFlagsArray[@]}"}
${checkFlags:-VERBOSE=y} ${checkFlagsArray+"${checkFlagsArray[@]}"}
${checkTarget:-check}
)
echoCmd 'check flags' "${flagsArray[@]}"
make ${makefile:+-f $makefile} "${flagsArray[@]}"
@ -797,10 +850,13 @@ installPhase() {
installTargets="${installTargets:-install}"
# Old bash empty array hack
# shellcheck disable=SC2086
local flagsArray=( $installTargets \
$makeFlags "${makeFlagsArray[@]}" \
$installFlags "${installFlagsArray[@]}")
local flagsArray=(
$installTargets
$makeFlags ${makeFlagsArray+"${makeFlagsArray[@]}"}
$installFlags ${installFlagsArray+"${installFlagsArray[@]}"}
)
echoCmd 'install flags' "${flagsArray[@]}"
make ${makefile:+-f $makefile} "${flagsArray[@]}"
@ -830,39 +886,39 @@ fixupPhase() {
# Propagate build inputs and setup hook into the development output.
if [ -z "$crossConfig" ]; then
if [ -z "${crossConfig:-}" ]; then
# Not cross-compiling - propagatedBuildInputs are handled identically to propagatedNativeBuildInputs
local propagated="$propagatedNativeBuildInputs"
if [ -n "$propagatedBuildInputs" ]; then
if [ -n "${propagatedBuildInputs:-}" ]; then
propagated+="${propagated:+ }$propagatedBuildInputs"
fi
if [ -n "$propagated" ]; then
if [ -n "${propagated:-}" ]; then
mkdir -p "${!outputDev}/nix-support"
# shellcheck disable=SC2086
printWords $propagated > "${!outputDev}/nix-support/propagated-native-build-inputs"
fi
else
if [ -n "$propagatedBuildInputs" ]; then
if [ -n "${propagatedBuildInputs:-}" ]; then
mkdir -p "${!outputDev}/nix-support"
# shellcheck disable=SC2086
printWords $propagatedBuildInputs > "${!outputDev}/nix-support/propagated-build-inputs"
fi
if [ -n "$propagatedNativeBuildInputs" ]; then
if [ -n "${propagatedNativeBuildInputs:-}" ]; then
mkdir -p "${!outputDev}/nix-support"
# shellcheck disable=SC2086
printWords $propagatedNativeBuildInputs > "${!outputDev}/nix-support/propagated-native-build-inputs"
fi
fi
if [ -n "$setupHook" ]; then
if [ -n "${setupHook:-}" ]; then
mkdir -p "${!outputDev}/nix-support"
substituteAll "$setupHook" "${!outputDev}/nix-support/setup-hook"
fi
# Propagate user-env packages into the output with binaries, TODO?
if [ -n "$propagatedUserEnvPkgs" ]; then
if [ -n "${propagatedUserEnvPkgs:-}" ]; then
mkdir -p "${!outputBin}/nix-support"
# shellcheck disable=SC2086
printWords $propagatedUserEnvPkgs > "${!outputBin}/nix-support/propagated-user-env-packages"
@ -875,11 +931,14 @@ fixupPhase() {
installCheckPhase() {
runHook preInstallCheck
# Old bash empty array hack
# shellcheck disable=SC2086
local flagsArray=( \
${enableParallelBuilding:+-j${NIX_BUILD_CORES} -l${NIX_BUILD_CORES}} \
$makeFlags "${makeFlagsArray[@]}" \
$installCheckFlags "${installCheckFlagsArray[@]}" ${installCheckTarget:-installcheck})
local flagsArray=(
${enableParallelBuilding:+-j${NIX_BUILD_CORES} -l${NIX_BUILD_CORES}}
$makeFlags ${makeFlagsArray+"${makeFlagsArray[@]}"}
$installCheckFlags ${installCheckFlagsArray+"${installCheckFlagsArray[@]}"}
${installCheckTarget:-installcheck}
)
echoCmd 'installcheck flags' "${flagsArray[@]}"
make ${makefile:+-f $makefile} "${flagsArray[@]}"
@ -892,13 +951,16 @@ installCheckPhase() {
distPhase() {
runHook preDist
# Old bash empty array hack
# shellcheck disable=SC2086
local flagsArray=($distFlags "${distFlagsArray[@]}" ${distTarget:-dist})
local flagsArray=(
$distFlags ${distFlagsArray+"${distFlagsArray[@]}"} ${distTarget:-dist}
)
echo 'dist flags: %q' "${flagsArray[@]}"
make ${makefile:+-f $makefile} "${flagsArray[@]}"
if [ "$dontCopyDist" != 1 ]; then
if [ "${dontCopyDist:-0}" != 1 ]; then
mkdir -p "$out/tarballs"
# Note: don't quote $tarballs, since we explicitly permit
@ -928,31 +990,37 @@ showPhaseHeader() {
genericBuild() {
if [ -f "$buildCommandPath" ]; then
. "$buildCommandPath"
if [ -f "${buildCommandPath:-}" ]; then
local oldOpts="$(shopt -po nounset)"
set +u
source "$buildCommandPath"
eval "$oldOpts"
return
fi
if [ -n "$buildCommand" ]; then
if [ -n "${buildCommand:-}" ]; then
local oldOpts="$(shopt -po nounset)"
set +u
eval "$buildCommand"
eval "$oldOpts"
return
fi
if [ -z "$phases" ]; then
phases="$prePhases unpackPhase patchPhase $preConfigurePhases \
configurePhase $preBuildPhases buildPhase checkPhase \
$preInstallPhases installPhase $preFixupPhases fixupPhase installCheckPhase \
$preDistPhases distPhase $postPhases";
if [ -z "${phases:-}" ]; then
phases="${prePhases:-} unpackPhase patchPhase ${preConfigurePhases:-} \
configurePhase ${preBuildPhases:-} buildPhase checkPhase \
${preInstallPhases:-} installPhase ${preFixupPhases:-} fixupPhase installCheckPhase \
${preDistPhases:-} distPhase ${postPhases:-}";
fi
for curPhase in $phases; do
if [[ "$curPhase" = buildPhase && -n "$dontBuild" ]]; then continue; fi
if [[ "$curPhase" = checkPhase && -z "$doCheck" ]]; then continue; fi
if [[ "$curPhase" = installPhase && -n "$dontInstall" ]]; then continue; fi
if [[ "$curPhase" = fixupPhase && -n "$dontFixup" ]]; then continue; fi
if [[ "$curPhase" = installCheckPhase && -z "$doInstallCheck" ]]; then continue; fi
if [[ "$curPhase" = distPhase && -z "$doDist" ]]; then continue; fi
if [[ "$curPhase" = buildPhase && -n "${dontBuild:-}" ]]; then continue; fi
if [[ "$curPhase" = checkPhase && -z "${doCheck:-}" ]]; then continue; fi
if [[ "$curPhase" = installPhase && -n "${dontInstall:-}" ]]; then continue; fi
if [[ "$curPhase" = fixupPhase && -n "${dontFixup:-}" ]]; then continue; fi
if [[ "$curPhase" = installCheckPhase && -z "${doInstallCheck:-}" ]]; then continue; fi
if [[ "$curPhase" = distPhase && -z "${doDist:-}" ]]; then continue; fi
if [[ -n "$tracePhases" ]]; then
if [[ -n "${tracePhases:-}" ]]; then
echo
echo "@ phase-started $out $curPhase"
fi
@ -962,13 +1030,16 @@ genericBuild() {
# Evaluate the variable named $curPhase if it exists, otherwise the
# function named $curPhase.
local oldOpts="$(shopt -po nounset)"
set +u
eval "${!curPhase:-$curPhase}"
eval "$oldOpts"
if [ "$curPhase" = unpackPhase ]; then
cd "${sourceRoot:-.}"
fi
if [ -n "$tracePhases" ]; then
if [ -n "${tracePhases:-}" ]; then
echo
echo "@ phase-succeeded $out $curPhase"
fi
@ -987,3 +1058,6 @@ runHook userHook
dumpVars
# Disable nounset for nix-shell.
set +u