Add load-config-file --path to load a different config (#3395)

* ipc: allow load-config to relocate the path of the config

* doc: add info about alternative configuration paths and relocating

Co-authored-by: Ivan Molodetskikh <yalterz@gmail.com>

* Update docs/wiki/Integrating-niri.md

* Update niri-ipc/src/lib.rs

* Update src/ipc/server.rs

---------

Co-authored-by: Ivan Molodetskikh <yalterz@gmail.com>

docs/wiki/Integrating-niri.md

@@ -11,6 +11,9 @@ When this file is present, niri *will not* automatically create a config at `~/.
 
 Keep in mind that we update the default config in new releases, so if you have a custom `/etc/niri/config.kdl`, you likely want to inspect and apply the relevant changes too.
 
+The default configuration locations can be overridden with the `NIRI_CONFIG` environment variable.
+You can also change the configuration path at runtime via the niri IPC or using the command `niri msg action load-config-file --path <path-to-config.kdl>`.
+
 You can split the niri config file into multiple files using [`include`](./Configuration:-Include.md).
 
 ### Xwayland

niri-config/src/binds.rs

@@ -368,7 +368,7 @@ pub enum Action {
     #[knuffel(skip)]
     UnsetWindowUrgent(u64),
     #[knuffel(skip)]
-    LoadConfigFile,
+    LoadConfigFile(#[knuffel(argument)] Option<String>),
     #[knuffel(skip)]
     MruAdvance {
         direction: MruDirection,
@@ -699,7 +699,7 @@ impl From<niri_ipc::Action> for Action {
             niri_ipc::Action::ToggleWindowUrgent { id } => Self::ToggleWindowUrgent(id),
             niri_ipc::Action::SetWindowUrgent { id } => Self::SetWindowUrgent(id),
             niri_ipc::Action::UnsetWindowUrgent { id } => Self::UnsetWindowUrgent(id),
-            niri_ipc::Action::LoadConfigFile {} => Self::LoadConfigFile,
+            niri_ipc::Action::LoadConfigFile { path } => Self::LoadConfigFile(path),
         }
     }
 }

niri-ipc/src/lib.rs

@@ -936,7 +936,13 @@ pub enum Action {
     ///
     /// Can be useful for scripts changing the config file, to avoid waiting the small duration for
     /// niri's config file watcher to notice the changes.
-    LoadConfigFile {},
+    LoadConfigFile {
+        /// Path of a new config file to load.
+        ///
+        /// If unset, reloads the current config file.
+        #[cfg_attr(feature = "clap", arg(long))]
+        path: Option<String>,
+    },
 }
 
 /// Change in window or column size.

src/input/mod.rs

@@ -2318,9 +2318,9 @@ impl State {
                 }
                 self.niri.queue_redraw_all();
             }
-            Action::LoadConfigFile => {
+            Action::LoadConfigFile(path) => {
                 if let Some(watcher) = &self.niri.config_file_watcher {
-                    watcher.load_config();
+                    watcher.load_config(path);
                 }
             }
             Action::MruConfirm => {

src/ipc/server.rs

@@ -463,7 +463,8 @@ async fn process(ctx: &ClientCtx, request: Request) -> Reply {
 fn validate_action(action: &Action) -> Result<(), String> {
     if let Action::Screenshot { path, .. }
     | Action::ScreenshotScreen { path, .. }
-    | Action::ScreenshotWindow { path, .. } = action
+    | Action::ScreenshotWindow { path, .. }
+    | Action::LoadConfigFile { path } = action
     {
         if let Some(path) = path {
             // Relative paths are resolved against the niri compositor's working directory, which
@@ -474,6 +475,13 @@ fn validate_action(action: &Action) -> Result<(), String> {
         }
     }
 
+    if let Action::LoadConfigFile { path: Some(path) } = action {
+        let p = Path::new(path);
+        if !p.is_file() {
+            return Err(format!("path does not point to a file: {path}"));
+        }
+    }
+
     Ok(())
 }
 

src/utils/watcher.rs

@@ -14,7 +14,7 @@ use crate::niri::State;
 const POLLING_INTERVAL: Duration = Duration::from_millis(500);
 
 pub struct Watcher {
-    load_config: mpsc::Sender<()>,
+    load_config: mpsc::Sender<Option<String>>,
 }
 
 struct WatcherInner {
@@ -67,7 +67,15 @@ impl Watcher {
 
                 loop {
                     let mut should_load = match load_config_rx.recv_timeout(POLLING_INTERVAL) {
-                        Ok(()) => true,
+                        Ok(path) => {
+                            if let Some(path) = path {
+                                inner = WatcherInner::new(
+                                    ConfigPath::Explicit(PathBuf::from(path)),
+                                    Vec::new(),
+                                );
+                            }
+                            true
+                        }
                         Err(mpsc::RecvTimeoutError::Disconnected) => break,
                         Err(mpsc::RecvTimeoutError::Timeout) => false,
                     };
@@ -105,8 +113,8 @@ impl Watcher {
         Self { load_config }
     }
 
-    pub fn load_config(&self) {
+    pub fn load_config(&self, path: Option<String>) {
-        let _ = self.load_config.send(());
+        let _ = self.load_config.send(path);
     }
 }