Add --dry-run (-n) flag to create and destroy commands

Shows the exact dladm/zonecfg/zoneadm commands, IPAM allocation, and
registry writes that would happen — without executing anything. Useful
for validating template + pool config before committing to a zone install.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/main.rs

@@ -32,6 +32,10 @@ struct Cli {
     #[arg(long, default_value = "/etc/zmgr")]
     registry: String,
 
+    /// Show what would be done without executing system commands
+    #[arg(long, short = 'n')]
+    dry_run: bool,
+
     #[command(subcommand)]
     command: Commands,
 }
@@ -124,10 +128,14 @@ fn main() -> miette::Result<()> {
     let cli = Cli::parse();
     let registry = std::path::PathBuf::from(&cli.registry);
 
+    let dry_run = cli.dry_run;
+
     match cli.command {
         Commands::Init { force } => cmd_init(&registry, force),
-        Commands::Create { name, template } => cmd_create(&registry, &name, template.as_deref()),
-        Commands::Destroy { name } => cmd_destroy(&registry, &name),
+        Commands::Create { name, template } => {
+            cmd_create(&registry, &name, template.as_deref(), dry_run)
+        }
+        Commands::Destroy { name } => cmd_destroy(&registry, &name, dry_run),
         Commands::List => cmd_list(&registry),
         Commands::Status { name } => cmd_status(&registry, name.as_deref()),
         Commands::Import { name } => cmd_import(&registry, name.as_deref()),
@@ -172,7 +180,12 @@ fn cmd_init(registry: &Path, force: bool) -> Result<()> {
     Ok(())
 }
 
-fn cmd_create(registry: &Path, name: &str, template_name: Option<&str>) -> Result<()> {
+fn cmd_create(
+    registry: &Path,
+    name: &str,
+    template_name: Option<&str>,
+    dry_run: bool,
+) -> Result<()> {
     config::ensure_initialized(registry)?;
 
     if Zone::exists(registry, name) {
@@ -194,9 +207,6 @@ fn cmd_create(registry: &Path, name: &str, template_name: Option<&str>) -> Resul
     let address = format!("{ip}/{prefix_len}");
     let vnic = format!("{name}0");
 
-    // Create VNIC
-    exec::dladm_create_vnic(&vnic, &pool.stub)?;
-
     // Build zonecfg commands
     let autoboot = if tmpl.autoboot { "true" } else { "false" };
     let zonecfg_cmds = format!(
@@ -215,6 +225,40 @@ fn cmd_create(registry: &Path, name: &str, template_name: Option<&str>) -> Resul
         cfg.zonepath_prefix, tmpl.brand, tmpl.ip_type, pool.gateway
     );
 
+    if dry_run {
+        println!("[dry-run] Would create zone '{name}'");
+        println!();
+        println!("  template:  {tmpl_name}");
+        println!("  brand:     {}", tmpl.brand);
+        println!("  address:   {address}");
+        println!("  vnic:      {vnic} (on stub {})", pool.stub);
+        println!("  gateway:   {}", pool.gateway);
+        println!("  zonepath:  {}/{name}", cfg.zonepath_prefix);
+        println!("  autoboot:  {}", tmpl.autoboot);
+        println!();
+        println!("Commands that would be executed:");
+        println!();
+        println!("  dladm create-vnic -l {} {vnic}", pool.stub);
+        println!();
+        println!("  zonecfg -z {name} <<EOF");
+        for line in zonecfg_cmds.lines() {
+            println!("  {line}");
+        }
+        println!("  EOF");
+        println!();
+        println!("  zoneadm -z {name} install");
+        if tmpl.autoboot {
+            println!("  zoneadm -z {name} boot");
+        }
+        println!();
+        println!("Registry entry that would be written:");
+        println!("  {}/zones/{name}.kdl", registry.display());
+        return Ok(());
+    }
+
+    // Create VNIC
+    exec::dladm_create_vnic(&vnic, &pool.stub)?;
+
     exec::zonecfg_create(name, &zonecfg_cmds)?;
     exec::zoneadm_install(name)?;
 
@@ -249,11 +293,30 @@ fn cmd_create(registry: &Path, name: &str, template_name: Option<&str>) -> Resul
     Ok(())
 }
 
-fn cmd_destroy(registry: &Path, name: &str) -> Result<()> {
+fn cmd_destroy(registry: &Path, name: &str, dry_run: bool) -> Result<()> {
     config::ensure_initialized(registry)?;
 
     let zone = Zone::load(registry, name)?;
 
+    if dry_run {
+        println!("[dry-run] Would destroy zone '{name}'");
+        println!();
+        println!("  template:  {}", zone.template);
+        println!("  address:   {}", zone.address);
+        println!("  vnic:      {}", zone.vnic);
+        println!();
+        println!("Commands that would be executed:");
+        println!();
+        println!("  zoneadm -z {name} halt");
+        println!("  zoneadm -z {name} uninstall -F");
+        println!("  zonecfg -z {name} delete -F");
+        println!("  dladm delete-vnic {}", zone.vnic);
+        println!();
+        println!("Registry entry that would be removed:");
+        println!("  {}/zones/{name}.kdl", registry.display());
+        return Ok(());
+    }
+
     // Halt if running (ignore errors — zone may already be halted)
     let _ = exec::zoneadm_halt(name);