Print message when output was not found

niri-ipc/src/lib.rs

@@ -58,6 +58,8 @@ pub enum Response {
     Outputs(HashMap<String, Output>),
     /// Information about the focused window.
     FocusedWindow(Option<Window>),
+    /// Output configuration change result.
+    OutputConfigChanged(OutputConfigChanged),
 }
 
 /// Actions that niri can perform.
@@ -456,6 +458,15 @@ pub struct Window {
     pub app_id: Option<String>,
 }
 
+/// Output configuration change result.
+#[derive(Serialize, Deserialize, Debug, Clone, Copy, PartialEq, Eq)]
+pub enum OutputConfigChanged {
+    /// The target output was connected and the change was applied.
+    Applied,
+    /// The target output was not found, the change will be applied when it is connected.
+    OutputWasMissing,
+}
+
 impl FromStr for SizeChange {
     type Err = &'static str;
 

src/ipc/client.rs

@@ -1,5 +1,7 @@
 use anyhow::{anyhow, bail, Context};
-use niri_ipc::{LogicalOutput, Mode, Output, Request, Response, Socket, Transform};
+use niri_ipc::{
+    LogicalOutput, Mode, Output, OutputConfigChanged, Request, Response, Socket, Transform,
+};
 use serde_json::json;
 
 use crate::cli::Msg;
@@ -241,10 +243,15 @@ pub fn handle_msg(msg: Msg, json: bool) -> anyhow::Result<()> {
                 bail!("unexpected response: expected Handled, got {response:?}");
             };
         }
-        Msg::Output { .. } => {
-            let Response::Handled = response else {
-                bail!("unexpected response: expected Handled, got {response:?}");
+        Msg::Output { output, .. } => {
+            let Response::OutputConfigChanged(response) = response else {
+                bail!("unexpected response: expected OutputConfigChanged, got {response:?}");
             };
+
+            if response == OutputConfigChanged::OutputWasMissing {
+                println!("Output \"{output}\" is not connected.");
+                println!("The change will apply when it is connected.");
+            }
         }
     }
 

src/ipc/server.rs

@@ -8,7 +8,7 @@ use calloop::io::Async;
 use directories::BaseDirs;
 use futures_util::io::{AsyncReadExt, BufReader};
 use futures_util::{AsyncBufReadExt, AsyncWriteExt};
-use niri_ipc::{Reply, Request, Response};
+use niri_ipc::{OutputConfigChanged, Reply, Request, Response};
 use smithay::desktop::Window;
 use smithay::reexports::calloop::generic::Generic;
 use smithay::reexports::calloop::{Interest, LoopHandle, Mode, PostAction};
@@ -170,10 +170,19 @@ fn process(ctx: &ClientCtx, request: Request) -> Reply {
             Response::Handled
         }
         Request::Output { output, action } => {
+            let ipc_outputs = ctx.ipc_outputs.lock().unwrap();
+            let response = if ipc_outputs.contains_key(&output) {
+                OutputConfigChanged::Applied
+            } else {
+                OutputConfigChanged::OutputWasMissing
+            };
+            drop(ipc_outputs);
+
             ctx.event_loop.insert_idle(move |state| {
                 state.apply_transient_output_config(&output, action);
             });
-            Response::Handled
+
+            Response::OutputConfigChanged(response)
         }
     };