config: enable customization of behaviour upon an error condition

tracing-tracy/src/config.rs

@@ -57,6 +57,26 @@ pub trait Config {
     fn format_fields_in_zone_name(&self) -> bool {
         true
     }
+
+    /// Apply handling for errors detected by the [`TracyLayer`].
+    ///
+    /// Fundamentally the way the tracing crate and the Tracy profiler work are somewhat
+    /// incompatible in certain ways. For instance, a [`tracing::Span`] can be created on one
+    /// thread and moved to another, where it is cleaned up. Tracy on the other hand expects that
+    /// its eqvivalent concept of zone remains entirely within a thread.
+    ///
+    /// Another example a limitation in `Tracy` where the message length or zone name cannot exceed
+    /// a certain (low) limit of bytes.
+    ///
+    /// Although `tracing_tracy` does it best to paper over these sorts of differences, it can’t
+    /// always make them invisible. In certain cases detecting these sorts of issues is
+    /// straightforward, and it is when `tracing_tracy` will invoke this method to enable users to
+    /// report the issues in whatever way they wish to.
+    ///
+    /// By default a message coloured in red is emitted to the tracy client.
+    fn on_error(&self, client: &Client, error: &'static str) {
+        client.color_message(error, 0xFF000000, self.stack_depth());
+    }
 }
 
 /// A type that implements the [`Config`] trait with runtime-adjustable values.

tracing-tracy/src/lib.rs

@@ -132,8 +132,7 @@ impl<C: Config> TracyLayer<C> {
             while !data.is_char_boundary(max_len) {
                 max_len -= 1;
             }
-            self.client
-                .color_message(error_msg, 0xFF000000, self.config.stack_depth());
+            self.config.on_error(&self.client, error_msg);
             &data[..max_len]
         } else {
             data
@@ -298,19 +297,17 @@ where
 
         if let Some((span, span_id)) = stack_frame {
             if id.into_u64() != span_id {
-                self.client.color_message(
+                self.config.on_error(
+                    &self.client,
                     "Tracing spans exited out of order! \
-                        Trace may not be accurate for this span stack.",
-                    0xFF000000,
-                    self.config.stack_depth(),
+                        Trace might not be accurate for this span stack.",
                 );
             }
             drop(span);
         } else {
-            self.client.color_message(
+            self.config.on_error(
+                &self.client,
                 "Exiting a tracing span, but got nothing on the tracy span stack!",
-                0xFF000000,
-                self.config.stack_depth(),
             );
         }
     }