src/NLog/LayoutRenderers/MessageLayoutRenderer.cs (2)

95-103: Robust exception rendering path — good. One edge-case to verify.
If the message is empty (e.g., Raw with ""), ExceptionSeparator is still appended, producing a leading separator. Confirm this matches prior behavior; if not, gate the separator on whether this renderer appended any message content.

Possible tweak (requires capturing start length earlier in Append):

 protected override void Append(StringBuilder builder, LogEventInfo logEvent)
 {
+    int startLen = builder.Length;
@@
-                if (!exceptionOnly)
-                    builder.Append(ExceptionSeparator);
+                if (!exceptionOnly && builder.Length > startLen)
+                    builder.Append(ExceptionSeparator);
                 AppendExceptionToString(builder, primaryException);
 }

---

105-126: Fallback should include all AggregateException inners; trim allocations.
When ToString() throws on an AggregateException with multiple inners, only InnerException is rendered. Iterate InnerExceptions in the fallback and avoid interpolation to reduce temps.

Apply within the catch:

-            catch (Exception ex)
-            {
-                InternalLogger.Warn(ex, "Message-LayoutRenderer Could not output ToString for Exception: {0}", exception.GetType());
-                builder.Append($"{exception.GetType()}: {exceptionMessage}");
-                if (innerException != null)
-                {
-                    builder.AppendLine();
-                    AppendExceptionToString(builder, innerException);
-                }
-            }
+            catch (Exception ex)
+            {
+                InternalLogger.Warn(ex, "Message-LayoutRenderer failed to call ToString() on {0}", exception.GetType());
+                var typeName = exception.GetType().FullName ?? exception.GetType().Name;
+                builder.Append(typeName);
+                if (!string.IsNullOrEmpty(exceptionMessage))
+                {
+                    builder.Append(": ");
+                    builder.Append(exceptionMessage);
+                }
+
+                if (exception is AggregateException agg && agg.InnerExceptions?.Count > 0)
+                {
+                    foreach (var ie in agg.InnerExceptions)
+                    {
+                        builder.AppendLine();
+                        AppendExceptionToString(builder, ie);
+                    }
+                }
+                else if (innerException != null)
+                {
+                    builder.AppendLine();
+                    AppendExceptionToString(builder, innerException);
+                }
+            }

Also consider a simple recursion cap (e.g., max depth 16) to prevent pathological cycles.

Would you like a small unit test that defines an Exception whose ToString() throws and asserts the fallback (including multiple AggregateException inners)?

Configuration used: CodeRabbit UI

Review profile: CHILL

Plan: Pro

src/NLog/LayoutRenderers/ExceptionLayoutRenderer.cs (1)

441-446: Avoid losing the fallback Message when InnerException getter throws

Reordering means if ex.InnerException throws before exceptionMessage is captured, the fallback becomes Type: with an empty message. Capturing Message first preserves more signal in that failure mode.

Apply minimal swap:

-                innerException = ex.InnerException;
-                exceptionMessage = ex.Message;
+                exceptionMessage = ex.Message;
+                innerException = ex.InnerException;

Alternative (more robust): capture both properties in separate try/catch blocks before calling ToString() so either getter failing doesn’t hide the other.

Configuration used: CodeRabbit UI

Review profile: CHILL

Plan: Pro