support runtimes without TracingChannel.hasSubscribers aggregate

Bun's node:diagnostics_channel ships TracingChannel but does not expose the
aggregate hasSubscribers getter, so a subscriber added via
tracingChannel.subscribe(handlers) is invisible to the previous
?.hasSubscribers gate and graphql-js silently drops every event.

Introduce a shouldTrace helper that trusts the aggregate when present and
falls back to checking each of the five underlying lifecycle channels when
it is undefined. Route every emission gate (parse/validate/execute/
subscribe/resolve) through it.

Author: logaretm

src/diagnostics.ts

@@ -20,6 +20,7 @@ import { isPromise } from './jsutils/isPromise.js';
  * @internal
  */
 export interface MinimalChannel {
+  readonly hasSubscribers?: boolean;
   publish: (message: unknown) => void;
   runStores: <T, ContextType extends object>(
     context: ContextType,
@@ -37,7 +38,9 @@ export interface MinimalChannel {
  * @internal
  */
 export interface MinimalTracingChannel {
-  readonly hasSubscribers: boolean;
+  // `undefined` accommodates runtimes (e.g. Bun) that ship `tracingChannel`
+  // without exposing the aggregate `hasSubscribers` getter.
+  readonly hasSubscribers: boolean | undefined;
   readonly start: MinimalChannel;
   readonly end: MinimalChannel;
   readonly asyncStart: MinimalChannel;
@@ -126,6 +129,33 @@ export const subscribeChannel: MinimalTracingChannel | undefined =
 export const resolveChannel: MinimalTracingChannel | undefined =
   dc?.tracingChannel('graphql:resolve');
 
+const SUB_CHANNEL_KEYS: ReadonlyArray<
+  'start' | 'end' | 'asyncStart' | 'asyncEnd' | 'error'
+> = ['start', 'end', 'asyncStart', 'asyncEnd', 'error'];
+
+/**
+ * Whether emission sites should publish to `channel`. Trusts the
+ * `TracingChannel.hasSubscribers` aggregate when the runtime exposes it; if
+ * the getter is missing (e.g. Bun's `node:diagnostics_channel`, where
+ * `tracingChannel.hasSubscribers` is `undefined`), falls back to checking
+ * each of the five underlying lifecycle channels so a subscriber attached
+ * via `tracingChannel.subscribe(handlers)` is still observed.
+ *
+ * @internal
+ */
+export function shouldTrace(
+  channel: MinimalTracingChannel | undefined,
+): channel is MinimalTracingChannel {
+  if (channel == null) {
+    return false;
+  }
+  const aggregate = channel.hasSubscribers;
+  if (aggregate !== undefined) {
+    return aggregate;
+  }
+  return SUB_CHANNEL_KEYS.some((key) => channel[key].hasSubscribers === true);
+}
+
 /**
  * Publish a mixed sync-or-promise operation through `channel`. Caller has
  * already verified that a subscriber is attached.

src/execution/Executor.ts

@@ -44,7 +44,7 @@ import {
 } from '../type/definition.js';
 import type { GraphQLSchema } from '../type/schema.js';
 
-import { resolveChannel, traceMixed } from '../diagnostics.js';
+import { resolveChannel, shouldTrace, traceMixed } from '../diagnostics.js';
 
 import { AbortedGraphQLExecutionError } from './AbortedGraphQLExecutionError.js';
 import { withCancellation } from './cancellablePromise.js';
@@ -589,7 +589,7 @@ export class Executor<
     const returnType = fieldDef.type;
     let resolveFn = fieldDef.resolve ?? validatedExecutionArgs.fieldResolver;
 
-    if (resolveChannel?.hasSubscribers) {
+    if (shouldTrace(resolveChannel)) {
       const channel = resolveChannel;
       const originalResolveFn = resolveFn;
       resolveFn = (s, args, c, info) =>

src/execution/execute.ts

@@ -36,6 +36,7 @@ import { getOperationAST } from '../utilities/getOperationAST.js';
 
 import {
   executeChannel,
+  shouldTrace,
   subscribeChannel,
   traceMixed,
 } from '../diagnostics.js';
@@ -74,7 +75,7 @@ const UNEXPECTED_EXPERIMENTAL_DIRECTIVES =
  * delivery.
  */
 export function execute(args: ExecutionArgs): PromiseOrValue<ExecutionResult> {
-  if (!executeChannel?.hasSubscribers) {
+  if (!shouldTrace(executeChannel)) {
     return executeImpl(args);
   }
   return traceMixed(executeChannel, buildExecuteCtxFromArgs(args), () =>
@@ -138,7 +139,7 @@ function executeImpl(args: ExecutionArgs): PromiseOrValue<ExecutionResult> {
 export function experimentalExecuteIncrementally(
   args: ExecutionArgs,
 ): PromiseOrValue<ExecutionResult | ExperimentalIncrementalExecutionResults> {
-  if (!executeChannel?.hasSubscribers) {
+  if (!shouldTrace(executeChannel)) {
     return experimentalExecuteIncrementallyImpl(args);
   }
   return traceMixed(executeChannel, buildExecuteCtxFromArgs(args), () =>
@@ -166,7 +167,7 @@ function experimentalExecuteIncrementallyImpl(
 export function executeIgnoringIncremental(
   args: ExecutionArgs,
 ): PromiseOrValue<ExecutionResult | ExperimentalIncrementalExecutionResults> {
-  if (!executeChannel?.hasSubscribers) {
+  if (!shouldTrace(executeChannel)) {
     return executeIgnoringIncrementalImpl(args);
   }
   return traceMixed(executeChannel, buildExecuteCtxFromArgs(args), () =>
@@ -283,7 +284,7 @@ export function subscribe(
 ): PromiseOrValue<
   AsyncGenerator<ExecutionResult, void, void> | ExecutionResult
 > {
-  if (!subscribeChannel?.hasSubscribers) {
+  if (!shouldTrace(subscribeChannel)) {
     return subscribeImpl(args);
   }
   return traceMixed(subscribeChannel, buildExecuteCtxFromArgs(args), () =>
@@ -598,7 +599,7 @@ function mapSourceToResponse(
       ...validatedExecutionArgs,
       rootValue: payload,
     };
-    if (!executeChannel?.hasSubscribers) {
+    if (!shouldTrace(executeChannel)) {
       return validatedExecutionArgs.perEventExecutor(perEventExecutionArgs);
     }
     return traceMixed(

src/language/parser.ts

@@ -3,7 +3,7 @@ import type { Maybe } from '../jsutils/Maybe.js';
 import type { GraphQLError } from '../error/GraphQLError.js';
 import { syntaxError } from '../error/syntaxError.js';
 
-import { parseChannel } from '../diagnostics.js';
+import { parseChannel, shouldTrace } from '../diagnostics.js';
 
 import type {
   ArgumentCoordinateNode,
@@ -134,7 +134,7 @@ export function parse(
   source: string | Source,
   options?: ParseOptions,
 ): DocumentNode {
-  return parseChannel?.hasSubscribers
+  return shouldTrace(parseChannel)
     ? parseChannel.traceSync(() => parseImpl(source, options), { source })
     : parseImpl(source, options);
 }

src/validation/validate.ts

@@ -12,7 +12,7 @@ import { assertValidSchema } from '../type/validate.js';
 
 import { TypeInfo, visitWithTypeInfo } from '../utilities/TypeInfo.js';
 
-import { validateChannel } from '../diagnostics.js';
+import { shouldTrace, validateChannel } from '../diagnostics.js';
 
 import { specifiedRules, specifiedSDLRules } from './specifiedRules.js';
 import type { SDLValidationRule, ValidationRule } from './ValidationContext.js';
@@ -63,7 +63,7 @@ export function validate(
   rules: ReadonlyArray<ValidationRule> = specifiedRules,
   options?: ValidationOptions,
 ): ReadonlyArray<GraphQLError> {
-  return validateChannel?.hasSubscribers
+  return shouldTrace(validateChannel)
     ? validateChannel.traceSync(
         () => validateImpl(schema, documentAST, rules, options),
         { schema, document: documentAST },