install: configure and bootstrap synthetic.conf on darwin

Starting macOS 10.15 /nix can't be creasted directly anymore due to the
readonly filesystem, but synthetic.conf was introduced to enable
creating mountpoints or symlinks for special usecases like package
managers.

release.nix

@@ -177,10 +177,10 @@ let
         }
         ''
           cp ${installerClosureInfo}/registration $TMPDIR/reginfo
+          cp ${./scripts/create-darwin-volume.sh} $TMPDIR/create-darwin-volume.sh
           substitute ${./scripts/install-nix-from-closure.sh} $TMPDIR/install \
             --subst-var-by nix ${toplevel} \
             --subst-var-by cacert ${cacert}
-
           substitute ${./scripts/install-darwin-multi-user.sh} $TMPDIR/install-darwin-multi-user.sh \
             --subst-var-by nix ${toplevel} \
             --subst-var-by cacert ${cacert}
@@ -195,6 +195,7 @@ let
             # SC1090: Don't worry about not being able to find
             #         $nix/etc/profile.d/nix.sh
             shellcheck --exclude SC1090 $TMPDIR/install
+            shellcheck $TMPDIR/create-darwin-volume.sh
             shellcheck $TMPDIR/install-darwin-multi-user.sh
             shellcheck $TMPDIR/install-systemd-multi-user.sh
 
@@ -210,6 +211,7 @@ let
           fi
 
           chmod +x $TMPDIR/install
+          chmod +x $TMPDIR/create-darwin-volume.sh
           chmod +x $TMPDIR/install-darwin-multi-user.sh
           chmod +x $TMPDIR/install-systemd-multi-user.sh
           chmod +x $TMPDIR/install-multi-user
@@ -222,11 +224,15 @@ let
             --absolute-names \
             --hard-dereference \
             --transform "s,$TMPDIR/install,$dir/install," \
+            --transform "s,$TMPDIR/create-darwin-volume.sh,$dir/create-darwin-volume.sh," \
             --transform "s,$TMPDIR/reginfo,$dir/.reginfo," \
             --transform "s,$NIX_STORE,$dir/store,S" \
-            $TMPDIR/install $TMPDIR/install-darwin-multi-user.sh \
+            $TMPDIR/install \
+            $TMPDIR/create-darwin-volume.sh \
+            $TMPDIR/install-darwin-multi-user.sh \
             $TMPDIR/install-systemd-multi-user.sh \
-            $TMPDIR/install-multi-user $TMPDIR/reginfo \
+            $TMPDIR/install-multi-user \
+            $TMPDIR/reginfo \
             $(cat ${installerClosureInfo}/store-paths)
         '');
 

scripts/create-darwin-volume.sh

@@ -0,0 +1,107 @@
+#!/bin/sh
+set -e
+
+root_disks() {
+    diskutil list -plist /
+}
+
+apfs_volumes_for() {
+    disk=$1
+    diskutil apfs list -plist "$disk"
+}
+
+disk_identifier() {
+    xpath "/plist/dict/key[text()='WholeDisks']/following-sibling::array[1]/string/text()" 2>/dev/null
+}
+
+volume_get() {
+    key=$1 i=$2
+    xpath "/plist/dict/array/dict/key[text()='Volumes']/following-sibling::array/dict[$i]/key[text()='$key']/following-sibling::string[1]/text()" 2> /dev/null
+}
+
+find_nix_volume() {
+    disk=$1
+    i=1
+    volumes=$(apfs_volumes_for "$disk")
+    while true; do
+        name=$(echo "$volumes" | volume_get "Name" "$i")
+        if [ -z "$name" ]; then
+            break
+        fi
+        case "$name" in
+            [Nn]ix*)
+                echo "$name"
+                break
+                ;;
+        esac
+        i=$((i+1))
+    done
+}
+
+test_fstab() {
+    grep -q "/nix" /etc/fstab 2>/dev/null
+}
+
+test_synthetic_conf() {
+    grep -q "^nix" /etc/synthetic.conf 2>/dev/null
+}
+
+test_nix() {
+    test -d "/nix"
+}
+
+main() {
+    (
+        echo ""
+        echo "     ------------------------------------------------------------------ "
+        echo "    | This installer will create a volume for the nix store and        |"
+        echo "    | configure it to mount at /nix.  Follow these steps to uninstall. |"
+        echo "     ------------------------------------------------------------------ "
+        echo ""
+        echo "  1. Remove the entry from fstab using 'sudo vifs'"
+        echo "  2. Destroy the data volume using 'diskutil apfs deleteVolume'"
+        echo "  3. Delete /etc/synthetic.conf"
+        echo ""
+    ) >&2
+
+    if [ -L "/nix" ]; then
+        echo "error: /nix is a symlink, please remove it or edit synthetic.conf (requires reboot)" >&2
+        echo "  /nix -> $(readlink "/nix")" >&2
+        exit 2
+    fi
+
+    if ! test_synthetic_conf; then
+        echo "Configuring /etc/synthetic.conf..." >&2
+        echo nix | sudo tee /etc/synthetic.conf
+        /System/Library/Filesystems/apfs.fs/Contents/Resources/apfs.util -B
+    fi
+
+    if ! test_nix; then
+        echo "Creating mountpoint for /nix..." >&2
+        sudo mkdir /nix
+    fi
+
+    disk=$(root_disks | disk_identifier)
+    volume=$(find_nix_volume "$disk")
+    if [ -z "$volume" ]; then
+        echo "Creating a Nix Store volume..." >&2
+        sudo diskutil apfs addVolume "$disk" APFS 'Nix Store' -mountpoint /nix
+        volume="Nix Store"
+    else
+        echo "Using existing '$volume' volume" >&2
+    fi
+
+    if ! test_fstab; then
+        echo "Configuring /etc/fstab..." >&2
+        label=$(echo "$volume" | sed 's/ /\\040/g')
+        printf "\$a\nLABEL=%s /nix apfs rw\n.\nwq\n" "$label" | EDITOR=ed sudo vifs
+    fi
+
+    echo "The following options can be enabled to disable spotlight indexing" >&2
+    echo "of the volume, which might be desirable." >&2
+    echo "" >&2
+    echo "   $ mdutil -i off /nix" >&2
+    echo "" >&2
+}
+
+main "$@"

scripts/install-nix-from-closure.sh

@@ -40,18 +40,21 @@ elif [ "$(uname -s)" = "Linux" ] && [ -e /run/systemd/system ]; then
 fi
 
 INSTALL_MODE=no-daemon
-
+CREATE_DARWIN_VOLUME=0
 # handle the command line flags
-while [ "x${1:-}" != "x" ]; do
+while [ $# -gt 0 ]; do
-    if [ "x${1:-}" = "x--no-daemon" ]; then
+    case $1 in
-        INSTALL_MODE=no-daemon
+        --daemon)
-    elif [ "x${1:-}" = "x--daemon" ]; then
+            INSTALL_MODE=daemon;;
-        INSTALL_MODE=daemon
+        --no-daemon)
-    elif [ "x${1:-}" = "x--no-channel-add" ]; then
+            INSTALL_MODE=no-daemon;;
-        NIX_INSTALLER_NO_CHANNEL_ADD=1
+        --no-channel-add)
-    elif [ "x${1:-}" = "x--no-modify-profile" ]; then
+            NIX_INSTALLER_NO_CHANNEL_ADD=1;;
-        NIX_INSTALLER_NO_MODIFY_PROFILE=1
+        --no-modify-profile)
-    elif [ "x${1:-}" != "x" ]; then
+            NIX_INSTALLER_NO_MODIFY_PROFILE=1;;
+        --create-volume)
+            CREATE_DARWIN_VOLUME=1;;
+        *)
             (
                 echo "Nix Installer [--daemon|--no-daemon] [--no-channel-add] [--no-modify-profile]"
 
@@ -73,11 +76,26 @@ while [ "x${1:-}" != "x" ]; do
                 echo "                      is installed by default."
                 echo ""
             ) >&2
-        exit
+
+            if [ "$(uname -s)" = "Darwin" ]; then
+                (
+                    echo " --create-volume: Create an APFS volume for the store and create the /nix"
+                    echo "                  mountpoint for it using synthetic.conf."
+                    echo "                  (required on macOS >=10.15)"
+                    echo "                  See https://nixos.org/nix/manual/#sect-darwin-apfs-volume"
+                    echo ""
+                ) >&2
             fi
+            exit;;
+    esac
     shift
 done
 
+if [ "$(uname -s)" = "Darwin" ] && [ "$CREATE_DARWIN_VOLUME" = 1 ]; then
+    printf '\e[1;31mCreating volume and mountpoint /nix.\e[0m\n'
+    "$self/create-darwin-volume.sh"
+fi
+
 if [ "$INSTALL_MODE" = "daemon" ]; then
     printf '\e[1;31mSwitching to the Daemon-based Installer\e[0m\n'
     exec "$self/install-multi-user"
@@ -95,6 +113,15 @@ if ! [ -e $dest ]; then
     echo "directory $dest does not exist; creating it by running '$cmd' using sudo" >&2
     if ! sudo sh -c "$cmd"; then
         echo "$0: please manually run '$cmd' as root to create $dest" >&2
+        if [ "$(uname -s)" = "Darwin" ]; then
+            (
+                echo ""
+                echo "Installing on macOS >=10.15 requires relocating the store to an apfs volume."
+                echo "Use --create-volume or run the preparation steps manually."
+                echo "See https://nixos.org/nix/manual/#sect-darwin-apfs-volume."
+                echo ""
+            ) >&2
+        fi
         exit 1
     fi
 fi