add --vm-test mode for local vm tests

Update src/nixos-anywhere.sh

docs/quickstart.md

@@ -83,7 +83,23 @@ example uses a local directory on the source machine.
 5. On the target machine, make sure you have access as root via ssh by adding
    your SSH key to the file `authorized_keys` in the directory `/root/.ssh`
 
-6. You can now run **nixos-anywhere** from the command line as shown below,
+6. (Optional) Test your nixos and disko configuration:
+
+The following command will automatically test your nixos configuration and run disko inside a virtual machine, where
+
+- `<path to configuration>` is the path to the directory or repository
+  containing `flake.nix` and `disk-config.nix`
+
+- `<configuration name>` must match the name that immediately follows the
+  text `nixosConfigurations.` in the flake, as indicated by the comment in
+  the
+  [example](https://github.com/numtide/nixos-anywhere-examples/blob/main/flake.nix)).
+
+```
+nix run github:numtide/nixos-anywhere -- --flake <path to configuration>#<configuration name> root@<ip address>
+```
+
+7. You can now run **nixos-anywhere** from the command line as shown below,
    where:
 
    - `<path to configuration>` is the path to the directory or repository

src/nixos-anywhere.sh

@@ -46,6 +46,8 @@ Options:
   URL of the source Nix store to copy the nixos and disko closure from
 * --build-on-remote
   build the closure on the remote machine instead of locally and copy-closuring it
+* --vm-test
+  build the system and test the disk configuration inside a VM without installing it to the target.
 USAGE
 }
 
@@ -155,7 +157,9 @@ while [[ $# -gt 0 ]]; do
   --build-on-remote)
     build_on_remote=y
     ;;
-
+  --vm-test)
+    vm_test=y
+    ;;
   *)
     if [[ -z ${ssh_connection-} ]]; then
       ssh_connection="$1"
@@ -198,17 +202,19 @@ nix_build() {
     "$@"
 }
 
-if [[ -z ${ssh_connection-} ]]; then
-  abort "ssh-host must be set"
-fi
+if [[ -z ${vm_test-} ]]; then
+  if [[ -z ${ssh_connection-} ]]; then
+    abort "ssh-host must be set"
+  fi
 
-# we generate a temporary ssh keypair that we can use during nixos-anywhere
-ssh_key_dir=$(mktemp -d)
-trap 'rm -rf "$ssh_key_dir"' EXIT
-mkdir -p "$ssh_key_dir"
-# ssh-copy-id requires this directory
-mkdir -p "$HOME/.ssh/"
-ssh-keygen -t ed25519 -f "$ssh_key_dir"/nixos-anywhere -P "" -C "nixos-anywhere" >/dev/null
+  # we generate a temporary ssh keypair that we can use during nixos-anywhere
+  ssh_key_dir=$(mktemp -d)
+  trap 'rm -rf "$ssh_key_dir"' EXIT
+  mkdir -p "$ssh_key_dir"
+  # ssh-copy-id requires this directory
+  mkdir -p "$HOME/.ssh/"
+  ssh-keygen -t ed25519 -f "$ssh_key_dir"/nixos-anywhere -P "" -C "nixos-anywhere" >/dev/null
+fi
 
 # parse flake nixos-install style syntax, get the system attr
 if [[ -n ${flake-} ]]; then
@@ -222,6 +228,14 @@ if [[ -n ${flake-} ]]; then
     exit 1
   fi
   if [[ ${build_on_remote-n} == "n" ]]; then
+    if [[ -n ${vm_test-} ]]; then
+      exec nix build \
+        --print-out-paths \
+        --no-link \
+        -L \
+        "${nix_options[@]}" \
+        "${flake}#nixosConfigurations.\"${flakeAttr}\".config.system.build.installTest"
+    fi
     disko_script=$(nix_build "${flake}#nixosConfigurations.\"${flakeAttr}\".config.system.build.diskoScript")
     nixos_system=$(nix_build "${flake}#nixosConfigurations.\"${flakeAttr}\".config.system.build.toplevel")
   fi