fix(nextjs): Fix conditional root span handling for route handlers (#11608)

This should make our checks more robust.

Author: mydea

packages/nextjs/src/common/wrapRouteHandlerWithSentry.ts

@@ -8,6 +8,7 @@ import {
   getRootSpan,
   handleCallbackErrors,
   setHttpStatus,
+  spanToJSON,
   startSpan,
 } from '@sentry/core';
 import type { Span } from '@sentry/types';
@@ -24,32 +25,41 @@ function startOrUpdateSpan(spanName: string, cb: (rootSpan: Span) => Promise<Res
   const activeSpan = getActiveSpan();
   const rootSpan = activeSpan && getRootSpan(activeSpan);
 
-  if (rootSpan) {
-    rootSpan.updateName(spanName);
-    rootSpan.setAttributes({
-      [SEMANTIC_ATTRIBUTE_SENTRY_SOURCE]: 'route',
-      [SEMANTIC_ATTRIBUTE_SENTRY_OP]: 'http.server',
-      [SEMANTIC_ATTRIBUTE_SENTRY_ORIGIN]: 'auto.function.nextjs',
-    });
+  // We have different possible scenarios here:
+  // 1. If we have no root span, we just create a new span
+  // 2. We have a root span that that we want to update here
+  // 3. We have a root span that was already updated (e.g. if this is a nested call)
 
-    return cb(rootSpan);
-  } else {
+  const attributes = {
+    [SEMANTIC_ATTRIBUTE_SENTRY_SOURCE]: 'route',
+    [SEMANTIC_ATTRIBUTE_SENTRY_OP]: 'http.server',
+    [SEMANTIC_ATTRIBUTE_SENTRY_ORIGIN]: 'auto.function.nextjs',
+  } as const;
+
+  if (!rootSpan) {
     return startSpan(
       {
-        op: 'http.server',
         name: spanName,
         forceTransaction: true,
-        attributes: {
-          [SEMANTIC_ATTRIBUTE_SENTRY_SOURCE]: 'route',
-          [SEMANTIC_ATTRIBUTE_SENTRY_OP]: 'http.server',
-          [SEMANTIC_ATTRIBUTE_SENTRY_ORIGIN]: 'auto.function.nextjs',
-        },
-      },
-      (span: Span) => {
-        return cb(span);
+        attributes,
       },
+      cb,
     );
   }
+
+  // If `op` is set, we assume this was already processed before
+  // Probably this is a nested call, no need to update anything anymore
+  // OR, if we don't have next.span_type, we don't know where this comes from and don't want to mess with it
+  const existingAttributes = spanToJSON(rootSpan).data || {};
+  if (existingAttributes[SEMANTIC_ATTRIBUTE_SENTRY_OP] || !existingAttributes['next.span_type']) {
+    return cb(rootSpan);
+  }
+
+  // Finally, we want to update the root span, as the ones generated by next are often not good enough for us
+  rootSpan.updateName(spanName);
+  rootSpan.setAttributes(attributes);
+
+  return cb(rootSpan);
 }
 
 /**