Detect failure to install GUI log callback

crates/re_log/src/lib.rs

@@ -31,7 +31,7 @@ pub use log_once::{debug_once, error_once, info_once, trace_once, warn_once};
 
 pub use {
     channel_logger::*,
-    multi_logger::{add_boxed_logger, add_logger},
+    multi_logger::{add_boxed_logger, add_logger, MultiLoggerNotSetupError},
     setup::*,
 };
 

crates/re_log/src/multi_logger.rs

@@ -6,24 +6,32 @@ static MULTI_LOGGER: MultiLogger = MultiLogger::new();
 
 static HAS_MULTI_LOGGER: AtomicBool = AtomicBool::new(false);
 
+/// Produced when trying to install additional loggers when [`init`] has not been called.
+///
+/// This can happen for example when users of the `rerun` crate use the `spawn` method,
+/// and they aren't using `re_log`.
+#[derive(Clone, Copy, Debug)]
+pub struct MultiLoggerNotSetupError {}
+
 /// Install the multi-logger as the default logger.
 pub fn init() -> Result<(), log::SetLoggerError> {
     HAS_MULTI_LOGGER.store(true, SeqCst);
     log::set_logger(&MULTI_LOGGER)
 }
 
 /// Install an additional global logger.
-pub fn add_boxed_logger(logger: Box<dyn log::Log>) {
-    add_logger(Box::leak(logger));
+pub fn add_boxed_logger(logger: Box<dyn log::Log>) -> Result<(), MultiLoggerNotSetupError> {
+    add_logger(Box::leak(logger))
 }
 
 /// Install an additional global logger.
-pub fn add_logger(logger: &'static dyn log::Log) {
-    debug_assert!(
-        HAS_MULTI_LOGGER.load(SeqCst),
-        "You forgot to setup multi-logging"
-    );
-    MULTI_LOGGER.loggers.write().push(logger);
+pub fn add_logger(logger: &'static dyn log::Log) -> Result<(), MultiLoggerNotSetupError> {
+    if HAS_MULTI_LOGGER.load(SeqCst) {
+        MULTI_LOGGER.loggers.write().push(logger);
+        Ok(())
+    } else {
+        Err(MultiLoggerNotSetupError {})
+    }
 }
 
 /// Forward log messages to multiple [`log::log`] receivers.

crates/re_log/src/setup.rs

@@ -42,7 +42,7 @@ pub fn setup_native_logging() {
 
     let mut stderr_logger = env_logger::Builder::new();
     stderr_logger.parse_filters(&log_filter);
-    crate::add_boxed_logger(Box::new(stderr_logger.build()));
+    crate::add_boxed_logger(Box::new(stderr_logger.build())).expect("Failed to install logger");
 }
 
 #[cfg(target_arch = "wasm32")]
@@ -51,5 +51,6 @@ pub fn setup_web_logging() {
     log::set_max_level(log::LevelFilter::Debug);
     crate::add_boxed_logger(Box::new(crate::web_logger::WebLogger::new(
         log::LevelFilter::Debug,
-    )));
+    )))
+    .expect("Failed to install logger");
 }

crates/re_ui/examples/re_ui_example.rs

@@ -54,7 +54,7 @@ pub struct ExampleApp {
 impl ExampleApp {
     fn new(re_ui: re_ui::ReUi) -> Self {
         let (logger, text_log_rx) = re_log::ChannelLogger::new(re_log::LevelFilter::Info);
-        re_log::add_boxed_logger(Box::new(logger));
+        re_log::add_boxed_logger(Box::new(logger)).unwrap();
 
         let tree = egui_dock::Tree::new(vec![1, 2, 3]);
 

crates/re_viewer/src/app.rs

@@ -111,7 +111,12 @@ impl App {
         shutdown: std::sync::Arc<std::sync::atomic::AtomicBool>,
     ) -> Self {
         let (logger, text_log_rx) = re_log::ChannelLogger::new(re_log::LevelFilter::Info);
-        re_log::add_boxed_logger(Box::new(logger));
+        if re_log::add_boxed_logger(Box::new(logger)).is_err() {
+            // This can happen when `rerun` crate users call `spawn`. TODO(emilk): make `spawn` spawn a new process.
+            re_log::debug!(
+                "re_log not initialized - we won't see any log messages as GUI notifications"
+            );
+        }
 
         let state: AppState = storage
             .and_then(|storage| eframe::get_value(storage, eframe::APP_KEY))