allow startTransaction to take a sampleContext argument which gets passed to tracesSampler

Author: lobsterkatie

packages/hub/src/hub.ts

@@ -10,6 +10,7 @@ import {
   Hub as HubInterface,
   Integration,
   IntegrationClass,
+  SampleContext,
   Severity,
   Span,
   SpanContext,
@@ -369,8 +370,8 @@ export class Hub implements HubInterface {
   /**
    * @inheritDoc
    */
-  public startTransaction(context: TransactionContext): Transaction {
-    return this._callExtensionMethod('startTransaction', context);
+  public startTransaction(context: TransactionContext, sampleContext?: SampleContext): Transaction {
+    return this._callExtensionMethod('startTransaction', context, sampleContext);
   }
 
   /**

packages/minimal/src/index.ts

@@ -5,6 +5,7 @@ import {
   Event,
   Extra,
   Extras,
+  SampleContext,
   Severity,
   Transaction,
   TransactionContext,
@@ -205,7 +206,8 @@ export function _callOnClient(method: string, ...args: any[]): void {
  * Sentry.
  *
  * @param context Properties of the new `Transaction`.
+ * @param sampleContext Information given to the transaction sampling function
  */
-export function startTransaction(context: TransactionContext): Transaction {
-  return callOnHub('startTransaction', { ...context });
+export function startTransaction(context: TransactionContext, sampleContext?: SampleContext): Transaction {
+  return callOnHub('startTransaction', { ...context }, sampleContext);
 }

packages/tracing/src/hubextensions.ts

@@ -32,7 +32,7 @@ function traceHeaders(this: Hub): { [key: string]: string } {
  *
  * Mutates the given Transaction object and then returns the mutated object.
  */
-function sample<T extends Transaction>(hub: Hub, transaction: T): T {
+function sample<T extends Transaction>(hub: Hub, transaction: T, sampleContext: SampleContext = {}): T {
   const client = hub.getClient();
   const options = (client && client.getOptions()) || {};
 
@@ -47,8 +47,6 @@ function sample<T extends Transaction>(hub: Hub, transaction: T): T {
   // we have to test for a pre-existsing sampling decision, in case this transaction is a child transaction and has
   // inherited its parent's decision
   if (transaction.sampled === undefined) {
-    const sampleContext: SampleContext = {}; // TODO (kmclb) build context object
-
     // we would have bailed at the beginning if neither `tracesSampler` nor `tracesSampleRate` were defined, so one of
     // these should work; prefer the hook if so
     const sampleRate =
@@ -82,9 +80,9 @@ function sample<T extends Transaction>(hub: Hub, transaction: T): T {
 /**
  * {@see Hub.startTransaction}
  */
-function startTransaction(this: Hub, context: TransactionContext): Transaction {
+function startTransaction(this: Hub, context: TransactionContext, sampleContext?: SampleContext): Transaction {
   const transaction = new Transaction(context, this);
-  return sample(this, transaction);
+  return sample(this, transaction, sampleContext);
 }
 
 /**
@@ -95,9 +93,10 @@ export function startIdleTransaction(
   context: TransactionContext,
   idleTimeout?: number,
   onScope?: boolean,
+  sampleContext?: SampleContext,
 ): IdleTransaction {
   const transaction = new IdleTransaction(context, hub, idleTimeout, onScope);
-  return sample(hub, transaction);
+  return sample(hub, transaction, sampleContext);
 }
 
 /**

packages/types/src/hub.ts

@@ -6,7 +6,7 @@ import { Integration, IntegrationClass } from './integration';
 import { Scope } from './scope';
 import { Severity } from './severity';
 import { Span, SpanContext } from './span';
-import { Transaction, TransactionContext } from './transaction';
+import { SampleContext, Transaction, TransactionContext } from './transaction';
 import { User } from './user';
 
 /**
@@ -198,6 +198,7 @@ export interface Hub {
    * Sentry.
    *
    * @param context Properties of the new `Transaction`.
+   * @param sampleContext Information given to the transaction sampling function
    */
-  startTransaction(context: TransactionContext): Transaction;
+  startTransaction(context: TransactionContext, sampleContext?: SampleContext): Transaction;
 }

packages/types/src/options.ts

@@ -151,6 +151,10 @@ export interface Options {
    *
    * Can be defined in place of `tracesSampleRate`. If neither is defined, tracing is disabled.
    *
+   * `startTransaction` or `startIdleTransaction` accept a `sampleContext` argument, which is then passed to this
+   * function, meant to provide information on which to make a sampling decision. Additional information may be included
+   * automatically, depending on the SDK and any included integrations.
+   *
    * @returns A sample rate between 0 and 1 (0 drops the trace, 1 guarantees it will be sent).
    */
   tracesSampler?(traceContext: SampleContext): number;