fix(udev): print NixOS permanent form as services.udev.packages so it keeps the 70- name (#1654)

crates/fbuild-cli/src/cli/port_scan.rs

@@ -82,7 +82,7 @@ pub enum PortAction {
         group: Option<String>,
         /// Install the rules (asks for root with the desktop's polkit dialog,
         /// or sudo on a terminal). On NixOS they go to /run/udev/rules.d and
-        /// the permanent `services.udev.extraRules` form is printed.
+        /// the permanent `services.udev.packages` form is printed.
         #[arg(long, conflicts_with = "group")]
         install: bool,
     },

crates/fbuild-cli/src/cli/udev.rs

@@ -18,7 +18,7 @@
 //! This module only *renders* text. Installing is deliberately left to the
 //! caller: on NixOS `/etc` is generated from declarative config, so a written
 //! file there is both out-of-band and liable to be clobbered. What those users
-//! need is the content for `services.udev.extraRules`, not a mutation.
+//! need is the content for a `services.udev.packages` entry, not a mutation.
 
 /// Group granted access by generated rules. `plugdev` is the conventional
 /// choice for pluggable non-storage hardware and, unlike `dialout`, does not
@@ -110,8 +110,12 @@ pub fn render_udev_rules(vids: &[u16], group: Option<&str>) -> Option<String> {
         ));
     }
     out.push_str("#\n");
-    out.push_str("# On NixOS, paste the rules below into services.udev.extraRules instead;\n");
-    out.push_str("# /etc there is generated and a hand-written file will not persist.\n");
+    out.push_str("# On NixOS, ship the rules below as a services.udev.packages entry\n");
+    out.push_str(&format!(
+        "# (pkgs.writeTextDir \"lib/udev/rules.d/{UDEV_RULES_FILENAME}\" ...) instead;\n"
+    ));
+    out.push_str("# /etc there is generated, and services.udev.extraRules lands in\n");
+    out.push_str("# 99-local.rules, too late for uaccess.\n");
     out.push('\n');
 
     for vid in sorted {

crates/fbuild-cli/src/cli/udev_install.rs

@@ -359,13 +359,18 @@ pub fn run_install() -> Result<()> {
 }
 
 /// NixOS: the `/run` install is lost at reboot; this is the permanent form.
+/// It is a udev package rather than `services.udev.extraRules` because NixOS
+/// writes `extraRules` to `99-local.rules`, after `73-seat-late.rules`, so
+/// `uaccess` would never be applied (FastLED/fbuild#1654).
 pub fn nixos_snippet(rules: &str) -> String {
     let body: String = rules
         .lines()
         .filter(|l| l.starts_with("SUBSYSTEM=="))
-        .map(|l| format!("    {l}\n"))
+        .map(|l| format!("      {l}\n"))
         .collect();
-    format!("services.udev.extraRules = ''\n{body}'';\n")
+    format!(
+        "services.udev.packages = [\n  (pkgs.writeTextDir \"lib/udev/rules.d/{UDEV_RULES_FILENAME}\" ''\n{body}  '')\n];\n"
+    )
 }
 
 /// `/dev/bus/usb/BBB/DDD` nodes of attached devices from registry vendors

crates/fbuild-cli/src/cli/udev_install_tests.rs

@@ -184,6 +184,6 @@ fn nixos_snippet_wraps_only_the_rules() {
     let s = nixos_snippet("# header\nSUBSYSTEM==\"usb\", X\n");
     assert_eq!(
         s,
-        "services.udev.extraRules = ''\n    SUBSYSTEM==\"usb\", X\n'';\n"
+        "services.udev.packages = [\n  (pkgs.writeTextDir \"lib/udev/rules.d/70-fbuild.rules\" ''\n      SUBSYSTEM==\"usb\", X\n  '')\n];\n"
     );
 }