Clean up daemon handling

Split `common.sh` into the vars and functions definitions vs starting
the daemon (and possibly other initialization logic). This way,
`init.sh` can just `source` the former. Trying to start the daemon
before `nix.conf` is written will fail because `nix daemon` requires
`--experimental-features 'nix-command'`.

`killDaemon` is idempotent, so it's safe to call when no daemon is
running.

`startDaemon` and `killDaemon` use the PID (which is now exported to
subshells) to decide whether there is work to be done, rather than
`NIX_REMOTE`, which might conceivably be set differently even if a
daemon is running.

`startDaemon` and `killDaemon` can save/restore the old `NIX_REMOTE` as
`NIX_REMOTE_OLD`.

`init.sh` kills daemon before deleting everything (including the daemon
socket).

tests/common/vars-and-functions.sh.in

@@ -0,0 +1,215 @@
+set -e
+
+if [[ -z "${COMMON_VARS_AND_FUNCTIONS_SH_SOURCED-}" ]]; then
+
+COMMON_VARS_AND_FUNCTIONS_SH_SOURCED=1
+
+export PS4='+(${BASH_SOURCE[0]}:$LINENO) '
+
+export TEST_ROOT=$(realpath ${TMPDIR:-/tmp}/nix-test)/${TEST_NAME:-default}
+export NIX_STORE_DIR
+if ! NIX_STORE_DIR=$(readlink -f $TEST_ROOT/store 2> /dev/null); then
+    # Maybe the build directory is symlinked.
+    export NIX_IGNORE_SYMLINK_STORE=1
+    NIX_STORE_DIR=$TEST_ROOT/store
+fi
+export NIX_LOCALSTATE_DIR=$TEST_ROOT/var
+export NIX_LOG_DIR=$TEST_ROOT/var/log/nix
+export NIX_STATE_DIR=$TEST_ROOT/var/nix
+export NIX_CONF_DIR=$TEST_ROOT/etc
+export NIX_DAEMON_SOCKET_PATH=$TEST_ROOT/dSocket
+unset NIX_USER_CONF_FILES
+export _NIX_TEST_SHARED=$TEST_ROOT/shared
+if [[ -n $NIX_STORE ]]; then
+    export _NIX_TEST_NO_SANDBOX=1
+fi
+export _NIX_IN_TEST=$TEST_ROOT/shared
+export _NIX_TEST_NO_LSOF=1
+export NIX_REMOTE=${NIX_REMOTE_-}
+unset NIX_PATH
+export TEST_HOME=$TEST_ROOT/test-home
+export HOME=$TEST_HOME
+unset XDG_STATE_HOME
+unset XDG_DATA_HOME
+unset XDG_CONFIG_HOME
+unset XDG_CONFIG_DIRS
+unset XDG_CACHE_HOME
+mkdir -p $TEST_HOME
+
+export PATH=@bindir@:$PATH
+if [[ -n "${NIX_CLIENT_PACKAGE:-}" ]]; then
+  export PATH="$NIX_CLIENT_PACKAGE/bin":$PATH
+fi
+DAEMON_PATH="$PATH"
+if [[ -n "${NIX_DAEMON_PACKAGE:-}" ]]; then
+  DAEMON_PATH="${NIX_DAEMON_PACKAGE}/bin:$DAEMON_PATH"
+fi
+coreutils=@coreutils@
+
+export dot=@dot@
+export SHELL="@bash@"
+export PAGER=cat
+export busybox="@sandbox_shell@"
+
+export version=@PACKAGE_VERSION@
+export system=@system@
+
+export BUILD_SHARED_LIBS=@BUILD_SHARED_LIBS@
+
+export IMPURE_VAR1=foo
+export IMPURE_VAR2=bar
+
+cacheDir=$TEST_ROOT/binary-cache
+
+readLink() {
+    ls -l "$1" | sed 's/.*->\ //'
+}
+
+clearProfiles() {
+    profiles="$HOME"/.local/state/nix/profiles
+    rm -rf "$profiles"
+}
+
+clearStore() {
+    echo "clearing store..."
+    chmod -R +w "$NIX_STORE_DIR"
+    rm -rf "$NIX_STORE_DIR"
+    mkdir "$NIX_STORE_DIR"
+    rm -rf "$NIX_STATE_DIR"
+    mkdir "$NIX_STATE_DIR"
+    clearProfiles
+}
+
+clearCache() {
+    rm -rf "$cacheDir"
+}
+
+clearCacheCache() {
+    rm -f $TEST_HOME/.cache/nix/binary-cache*
+}
+
+startDaemon() {
+    # Don’t start the daemon twice, as this would just make it loop indefinitely
+    if [[ "${_NIX_TEST_DAEMON_PID-}" != '' ]]; then
+        return
+    fi
+    # Start the daemon, wait for the socket to appear.
+    rm -f $NIX_DAEMON_SOCKET_PATH
+    PATH=$DAEMON_PATH nix-daemon &
+    _NIX_TEST_DAEMON_PID=$!
+    export _NIX_TEST_DAEMON_PID
+    for ((i = 0; i < 300; i++)); do
+        if [[ -S $NIX_DAEMON_SOCKET_PATH ]]; then
+          DAEMON_STARTED=1
+          break;
+        fi
+        sleep 0.1
+    done
+    if [[ -z ${DAEMON_STARTED+x} ]]; then
+      fail "Didn’t manage to start the daemon"
+    fi
+    trap "killDaemon" EXIT
+    # Save for if daemon is killed
+    NIX_REMOTE_OLD=$NIX_REMOTE
+    export NIX_REMOTE=daemon
+}
+
+killDaemon() {
+    # Don’t fail trying to stop a non-existant daemon twice
+    if [[ "${_NIX_TEST_DAEMON_PID-}" == '' ]]; then
+        return
+    fi
+    kill $_NIX_TEST_DAEMON_PID
+    for i in {0..100}; do
+        kill -0 $_NIX_TEST_DAEMON_PID 2> /dev/null || break
+        sleep 0.1
+    done
+    kill -9 $_NIX_TEST_DAEMON_PID 2> /dev/null || true
+    wait $_NIX_TEST_DAEMON_PID || true
+    rm -f $NIX_DAEMON_SOCKET_PATH
+    # Indicate daemon is stopped
+    unset _NIX_TEST_DAEMON_PID
+    # Restore old nix remote
+    NIX_REMOTE=$NIX_REMOTE_OLD
+    trap "" EXIT
+}
+
+restartDaemon() {
+    [[ -z "${_NIX_TEST_DAEMON_PID:-}" ]] && return 0
+
+    killDaemon
+    startDaemon
+}
+
+if [[ $(uname) == Linux ]] && [[ -L /proc/self/ns/user ]] && unshare --user true; then
+    _canUseSandbox=1
+fi
+
+isDaemonNewer () {
+  [[ -n "${NIX_DAEMON_PACKAGE:-}" ]] || return 0
+  local requiredVersion="$1"
+  local daemonVersion=$($NIX_DAEMON_PACKAGE/bin/nix-daemon --version | cut -d' ' -f3)
+  [[ $(nix eval --expr "builtins.compareVersions ''$daemonVersion'' ''$requiredVersion''") -ge 0 ]]
+}
+
+requireDaemonNewerThan () {
+  isDaemonNewer "$1" || exit 99
+}
+
+canUseSandbox() {
+    if [[ ! $_canUseSandbox ]]; then
+        echo "Sandboxing not supported, skipping this test..."
+        return 1
+    fi
+
+    return 0
+}
+
+fail() {
+    echo "$1"
+    exit 1
+}
+
+expect() {
+    local expected res
+    expected="$1"
+    shift
+    "$@" || res="$?"
+    if [[ $res -ne $expected ]]; then
+        echo "Expected '$expected' but got '$res' while running '$*'"
+        return 1
+    fi
+    return 0
+}
+
+needLocalStore() {
+  if [[ "$NIX_REMOTE" == "daemon" ]]; then
+    echo "Can’t run through the daemon ($1), skipping this test..."
+    return 99
+  fi
+}
+
+# Just to make it easy to find which tests should be fixed
+buggyNeedLocalStore() {
+  needLocalStore
+}
+
+enableFeatures() {
+    local features="$1"
+    sed -i 's/experimental-features .*/& '"$features"'/' "$NIX_CONF_DIR"/nix.conf
+}
+
+set -x
+
+onError() {
+    set +x
+    echo "$0: test failed at:" >&2
+    for ((i = 1; i < ${#BASH_SOURCE[@]}; i++)); do
+        if [[ -z ${BASH_SOURCE[i]} ]]; then break; fi
+        echo "  ${FUNCNAME[i]} in ${BASH_SOURCE[i]}:${BASH_LINENO[i-1]}" >&2
+    done
+}
+
+trap onError ERR
+
+fi # COMMON_VARS_AND_FUNCTIONS_SH_SOURCED