test(diagnostics): cover tracing subscriber fallback

Author: yaacovCR

src/__tests__/diagnostics-test.ts

@@ -6,7 +6,7 @@ import { expect } from 'chai';
 
 import { invariant } from '../jsutils/invariant.ts';
 
-import type { MinimalTracingChannel } from '../diagnostics.ts';
+import type { MinimalChannel, MinimalTracingChannel } from '../diagnostics.ts';
 import {
   executeChannel,
   executeRootSelectionSetChannel,
@@ -54,6 +54,38 @@ describe('diagnostics', () => {
   });
 
   describe('shouldTrace', () => {
+    function makeSubChannel(hasSubscribers: boolean): MinimalChannel {
+      return {
+        hasSubscribers,
+        publish: () => undefined,
+        runStores<T, ContextType extends object>(
+          context: ContextType,
+          fn: (this: ContextType, ...args: Array<unknown>) => T,
+        ): T {
+          return fn.call(context);
+        },
+      };
+    }
+
+    function makeFallbackTracingChannel(
+      subscribedSubChannel?: keyof Pick<
+        MinimalTracingChannel,
+        'start' | 'end' | 'asyncStart' | 'asyncEnd' | 'error'
+      >,
+    ): MinimalTracingChannel {
+      return {
+        hasSubscribers: undefined,
+        start: makeSubChannel(subscribedSubChannel === 'start'),
+        end: makeSubChannel(subscribedSubChannel === 'end'),
+        asyncStart: makeSubChannel(subscribedSubChannel === 'asyncStart'),
+        asyncEnd: makeSubChannel(subscribedSubChannel === 'asyncEnd'),
+        error: makeSubChannel(subscribedSubChannel === 'error'),
+        traceSync<T>(fn: (...args: Array<unknown>) => T): T {
+          return fn();
+        },
+      };
+    }
+
     it('returns false when channel is undefined', () => {
       expect(shouldTrace(undefined)).to.equal(false);
     });
@@ -79,5 +111,10 @@ describe('diagnostics', () => {
         realTC.unsubscribe(handler);
       }
     });
+
+    it('falls back to sub-channel subscribers when aggregate is missing', () => {
+      expect(shouldTrace(makeFallbackTracingChannel('error'))).to.equal(true);
+      expect(shouldTrace(makeFallbackTracingChannel())).to.equal(false);
+    });
   });
 });

src/diagnostics.ts

@@ -280,14 +280,14 @@ function resolveDiagnosticsChannel(): DiagnosticsChannelModule | undefined {
       ) as DiagnosticsChannelModule;
     }
     // TODO: remove this code when we drop support for Node < 20.16>.
-    /* c8 ignore next 6 */
+    /* node:coverage ignore next 6 */
     if (!dc && typeof require === 'function') {
       // CJS fallback for runtimes that lack `process.getBuiltinModule`
       // (e.g. Node 20.0 - 20.15). ESM builds skip this branch because
       // `require` is undeclared there.
       dc = require('node:diagnostics_channel') as DiagnosticsChannelModule;
     }
-    /* c8 ignore next 3 */
+    /* node:coverage ignore next 3 */
   } catch {
     // diagnostics_channel not available on this runtime; tracing is a no-op.
   }
@@ -355,7 +355,6 @@ export function shouldTrace<TContext = unknown>(
   const aggregate = channel.hasSubscribers;
   if (aggregate !== undefined) {
     return aggregate;
-    /* c8 ignore start */
   }
   // Bun-only fallback, exercised by integrationTests/diagnostics-bun.
   for (const key of SUB_CHANNEL_KEYS) {
@@ -364,7 +363,6 @@ export function shouldTrace<TContext = unknown>(
     }
   }
   return false;
-  /* c8 ignore stop */
 }
 
 interface TraceLifecycleContext {