feat(tracing): Favour client options tracePropagationTargets

[AbhiPrasad]

ref #8352

As we work toward adding tracing without performance support, this PR updates the BrowserTracing integration to use and favour the top level tracePropagationTargets option if it exists.

This option was made top level in #8395

tracePropagationTargets is now part of the unified API for distributed tracing. It's also expected that electron/react native will behave the same way as well. This also leaves us the flexibility to extract tracing out of BrowserTracing, or create a new integration that just does tracing but no performance monitoring.

We can make sure this migration is smooth and easy to understand with a good set of docs, which is what I will be working on next. In these docs changes, we'll be updating the automatic instrumentation sections, and formally documented tracePropagationTargets as a high level option.

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser - ES5 CDN Bundle (gzipped + minified)	21.3 KB (+0.01% 🔺)
@sentry/browser - ES5 CDN Bundle (minified)	66.43 KB (0%)
@sentry/browser - ES6 CDN Bundle (gzipped + minified)	19.82 KB (0%)
@sentry/browser - ES6 CDN Bundle (minified)	58.9 KB (0%)
@sentry/browser - Webpack (gzipped + minified)	21.43 KB (0%)
@sentry/browser - Webpack (minified)	69.87 KB (0%)
@sentry/react - Webpack (gzipped + minified)	21.46 KB (0%)
@sentry/nextjs Client - Webpack (gzipped + minified)	49.51 KB (+0.26% 🔺)
@sentry/browser + @sentry/tracing - ES5 CDN Bundle (gzipped + minified)	28.91 KB (+0.1% 🔺)
@sentry/browser + @sentry/tracing - ES6 CDN Bundle (gzipped + minified)	27.15 KB (+0.13% 🔺)
@sentry/replay ES6 CDN Bundle (gzipped + minified)	49.34 KB (0%)
@sentry/replay - Webpack (gzipped + minified)	43.1 KB (0%)
@sentry/browser + @sentry/tracing + @sentry/replay - ES6 CDN Bundle (gzipped + minified)	68.51 KB (+0.06% 🔺)
@sentry/browser + @sentry/replay - ES6 CDN Bundle (gzipped + minified)	61.38 KB (-0.01% 🔽)

[mydea]

Hmm, does it make sense that the top-level options take precedence? 🤔 I think I would expect the options that are passed directly to the integration to "win", so:

this.options.tracePropagationTargets || (clientOptions && clientOptions.tracePropagationTargets);

? Not a big thing, as I don't expect this to happen too often, though :) So feel free to ignore.

[AbhiPrasad]

Yeah that's a fair perspective actually. Let's discuss this at our meeting.

[AbhiPrasad]

Based on our meeting we've made two decisions.

1. We'll be combining the arrays of both top level and integration set tracePropagationTargets
2. We'll be emitting a warning when both values are set.

[AbhiPrasad]

Detailed below I decided against the combining array approach, but added the warning in b098188

[AbhiPrasad]

I experimented with merging in two arrays - but found it would be confusing to users because of the deprecated tracingOrigins. Since we now have three different configs, I figured having one supercede the others is the easiest way to explain behaviour, and we can document this everywhere as well.

Here's a git patch with the logic I was testing with

diff --git a/packages/tracing-internal/src/browser/browsertracing.ts b/packages/tracing-internal/src/browser/browsertracing.ts
index 202f4fe7a..755aae6a3 100644
--- a/packages/tracing-internal/src/browser/browsertracing.ts
+++ b/packages/tracing-internal/src/browser/browsertracing.ts
@@ -177,9 +177,15 @@ export class BrowserTracing implements Integration {
 
   private _collectWebVitals: () => void;
 
+  // See `tracePropagationTargets` in `setupOnce` for why this is commented out.
+  // private _hasSetTracePropagationTargets: boolean = false;
+
   public constructor(_options?: Partial<BrowserTracingOptions>) {
     addTracingExtensions();
 
+    // eslint-disable-next-line deprecation/deprecation
+    // this._hasSetTracePropagationTargets = !!(_options && (_options.tracePropagationTargets || _options.tracingOrigins));
+
     this.options = {
       ...DEFAULT_BROWSER_TRACING_OPTIONS,
       ..._options,
@@ -229,8 +235,23 @@ export class BrowserTracing implements Integration {
       _experiments,
     } = this.options;
 
-    const tracePropagationTargets =
-      (clientOptions && clientOptions.tracePropagationTargets) || this.options.tracePropagationTargets;
+    const clientOptionsTracePropagationTargets = clientOptions && clientOptions.tracePropagationTargets;
+    // There are three ways to configure tracePropagationTargets:
+    // 1. via top level client option `tracePropagationTargets`
+    // 2. via BrowserTracing option `tracePropagationTargets`
+    // 3. via BrowserTracing option `tracingOrigins` (deprecated)
+    //
+    // To avoid confusion, favour top level client option `tracePropagationTargets`, and fallback to
+    // BrowserTracing option `tracePropagationTargets` and then `tracingOrigins` (deprecated).
+    // This is done as it minimizes bundle size (we don't have to have undefined checks).
+    //
+    // If both 1 and either one of 2 or 3 are set (from above), we log out a warning.
+    const tracePropagationTargets = clientOptionsTracePropagationTargets || this.options.tracePropagationTargets;
+    // This warning will be in a future release after 7.57.0 when we formally deprecated the
+    // BrowserTracing`tracePropagationTargets` option.
+    // if (__DEBUG_BUILD__ && this._hasSetTracePropagationTargets && clientOptionsTracePropagationTargets) {
+    //   logger.warn('[Tracing] You have set options for tracePropagationTargets in BrowserTracing and top level `Sentry.init`. The SDK is defaulting to use value for top level `tracePropagationTargets` in client.');
+    // }
 
     instrumentRouting(
       (context: TransactionContext) => {

I'm only going to be adding a warning as a result.