fix: Use correct flag for server tracing (#14250)

* fix: Use correct flag for server tracing

* changeset

* docs-and-error

* changeset

* unit tests

* typo

Author: elliott-with-the-longest-name-on-github

.changeset/ready-points-clap.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+fix: use correct flag for server tracing

.changeset/whole-sloths-visit.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+chore: Better docs and error message for missing `@opentelemetry/api` dependency

documentation/docs/30-advanced/68-observability.md

@@ -94,3 +94,7 @@ sdk.start();
 ```
 
 Now, server-side requests will begin generating traces, which you can view in Jaeger's web console at [localhost:16686](http://localhost:16686).
+
+## `@opentelemetry/api`
+
+SvelteKit uses `@opentelemetry/api` to generate its spans. This is declared as an optional peer dependency so that users not needing traces see no impact on install size or runtime performance. In most cases, if you're configuring your application to collect SvelteKit's spans, you'll end up installing a library like `@opentelemetry/sdk-node` or `@vercel/otel`, which in turn depend on `@opentelemetry/api`, which will satisfy SvelteKit's dependency as well. If you see an error from SvelteKit telling you it can't find `@opentelemetry/api`, it may just be because you haven't set up your trace collection yet. If you _have_ done that and are still seeing the error, you can install `@opentelemetry/api` yourself. 

packages/kit/src/exports/vite/index.js

@@ -339,7 +339,7 @@ async function kit({ svelte_config }) {
 					__SVELTEKIT_EMBEDDED__: s(kit.embedded),
 					__SVELTEKIT_EXPERIMENTAL__REMOTE_FUNCTIONS__: s(kit.experimental.remoteFunctions),
 					__SVELTEKIT_CLIENT_ROUTING__: s(kit.router.resolution === 'client'),
-					__SVELTEKIT_SERVER_TRACING_ENABLED__: s(kit.experimental.instrumentation.server),
+					__SVELTEKIT_SERVER_TRACING_ENABLED__: s(kit.experimental.tracing.server),
 					__SVELTEKIT_PAYLOAD__: new_config.build.ssr
 						? '{}'
 						: `globalThis.__sveltekit_${version_hash}`
@@ -355,7 +355,7 @@ async function kit({ svelte_config }) {
 					__SVELTEKIT_EMBEDDED__: s(kit.embedded),
 					__SVELTEKIT_EXPERIMENTAL__REMOTE_FUNCTIONS__: s(kit.experimental.remoteFunctions),
 					__SVELTEKIT_CLIENT_ROUTING__: s(kit.router.resolution === 'client'),
-					__SVELTEKIT_SERVER_TRACING_ENABLED__: s(kit.experimental.instrumentation.server),
+					__SVELTEKIT_SERVER_TRACING_ENABLED__: s(kit.experimental.tracing.server),
 					__SVELTEKIT_PAYLOAD__: 'globalThis.__sveltekit_dev'
 				};
 

packages/kit/src/runtime/telemetry/otel.js

@@ -15,7 +15,7 @@ if (__SVELTEKIT_SERVER_TRACING_ENABLED__) {
 		})
 		.catch(() => {
 			throw new Error(
-				'Tracing is enabled (see `config.kit.experimental.instrumentation.server` in your svelte.config.js), but `@opentelemetry/api` is not available. Have you installed it?'
+				'Tracing is enabled (see `config.kit.experimental.instrumentation.server` in your svelte.config.js), but `@opentelemetry/api` is not available. This error will likely resolve itself when you set up your tracing instrumentation in `instrumentation.server.js`. For more information, see https://svelte.dev/docs/kit/observability#opentelemetry-api'
 			);
 		});
 }

packages/kit/src/runtime/telemetry/otel.missing.spec.js

@@ -11,6 +11,6 @@ vi.mock('@opentelemetry/api', () => {
 test('otel should throw an error when tracing is enabled but @opentelemetry/api is not available', async () => {
 	const { otel } = await import('./otel.js');
 	await expect(otel).rejects.toThrow(
-		'Tracing is enabled (see `config.kit.experimental.instrumentation.server` in your svelte.config.js), but `@opentelemetry/api` is not available. Have you installed it?'
+		'Tracing is enabled (see `config.kit.experimental.instrumentation.server` in your svelte.config.js), but `@opentelemetry/api` is not available. This error will likely resolve itself when you set up your tracing instrumentation in `instrumentation.server.js`. For more information, see https://svelte.dev/docs/kit/observability#opentelemetry-api'
 	);
 });