feat(core)!: Update hasTracingEnabled to consider empty trace config

Author: mydea

docs/migration/v8-to-v9.md

@@ -68,6 +68,16 @@ Sentry.init({
 });
 ```
 
+- In previous versions, we determined if tracing is enabled (for Tracing Without Performance) by checking if either `tracesSampleRate` or `traceSampler` are _defined_ at all, in `Sentry.init()`. This means that e.g. the following config would lead to tracing without performance (=tracing being enabled, even if no spans would be started):
+
+```js
+Sentry.init({
+  tracesSampleRate: undefined,
+});
+```
+
+In v9, an `undefined` value will be treated the same as if the value is not defined at all. You'll need to set `tracesSampleRate: 0` if you want to enable tracing without performance.
+
 ### `@sentry/node`
 
 - When `skipOpenTelemetrySetup: true` is configured, `httpIntegration({ spans: false })` will be configured by default. This means that you no longer have to specify this yourself in this scenario. With this change, no spans are emitted once `skipOpenTelemetrySetup: true` is configured, without any further configuration being needed.

packages/browser/src/sdk.ts

@@ -1,6 +1,7 @@
 import {
   consoleSandbox,
   dedupeIntegration,
+  dropUndefinedKeys,
   functionToStringIntegration,
   getCurrentScope,
   getIntegrationsToSetup,
@@ -64,15 +65,10 @@ function applyDefaultOptions(optionsArg: BrowserOptions = {}): BrowserOptions {
     sendClientReports: true,
   };
 
-  // TODO: Instead of dropping just `defaultIntegrations`, we should simply
-  // call `dropUndefinedKeys` on the entire `optionsArg`.
-  // However, for this to work we need to adjust the `hasTracingEnabled()` logic
-  // first as it differentiates between `undefined` and the key not being in the object.
-  if (optionsArg.defaultIntegrations == null) {
-    delete optionsArg.defaultIntegrations;
-  }
-
-  return { ...defaultOptions, ...optionsArg };
+  return {
+    ...defaultOptions,
+    ...dropUndefinedKeys(optionsArg),
+  };
 }
 
 type ExtensionProperties = {

packages/core/src/utils/hasTracingEnabled.ts

@@ -19,5 +19,5 @@ export function hasTracingEnabled(
   const client = getClient();
   const options = maybeOptions || (client && client.getOptions());
   // eslint-disable-next-line deprecation/deprecation
-  return !!options && (options.enableTracing || 'tracesSampleRate' in options || 'tracesSampler' in options);
+  return !!options && (options.enableTracing || options.tracesSampleRate != null || !!options.tracesSampler);
 }

packages/core/test/lib/utils/hasTracingEnabled.test.ts

@@ -10,6 +10,10 @@ describe('hasTracingEnabled', () => {
     ['With tracesSampleRate', { tracesSampleRate }, true],
     ['With enableTracing=true', { enableTracing: true }, true],
     ['With enableTracing=false', { enableTracing: false }, false],
+    ['With enableTracing=undefined', { enableTracing: undefined }, false],
+    ['With tracesSampleRate=undefined', { tracesSampleRate: undefined }, false],
+    ['With tracesSampleRate=0', { tracesSampleRate: 0 }, true],
+    ['With tracesSampler=undefined', { tracesSampler: undefined }, false],
     ['With tracesSampler && enableTracing=false', { tracesSampler, enableTracing: false }, true],
     ['With tracesSampleRate && enableTracing=false', { tracesSampler, enableTracing: false }, true],
     ['With tracesSampler and tracesSampleRate', { tracesSampler, tracesSampleRate }, true],