Function _startRootSpan

packages/core/src/tracing/trace.ts:482–542

(
  spanArguments: SentrySpanArguments,
  scope: Scope,
  isolationScope: Scope,
  parentSampled?: boolean,
)

}

function _startRootSpan(
  spanArguments: SentrySpanArguments,
  scope: Scope,
  isolationScope: Scope,
  parentSampled?: boolean,
): SentrySpan {
  const client = getClient();
  const options: Partial<ClientOptions> = client?.getOptions() || {};

  const { name = '' } = spanArguments;

  const mutableSpanSamplingData = { spanAttributes: { ...spanArguments.attributes }, spanName: name, parentSampled };

  // we don't care about the decision for the moment; this is just a placeholder
  client?.emit('beforeSampling', mutableSpanSamplingData, { decision: false });

  // If hook consumers override the parentSampled flag, we will use that value instead of the actual one
  const finalParentSampled = mutableSpanSamplingData.parentSampled ?? parentSampled;
  const finalAttributes = mutableSpanSamplingData.spanAttributes;

  const currentPropagationContext = scope.getPropagationContext();
  const _isTracingSuppressed = isTracingSuppressed(scope);

  const [sampled, sampleRate, localSampleRateWasApplied] = _isTracingSuppressed
    ? [false]
    : sampleSpan(
        options,
        {
          name,
          parentSampled: finalParentSampled,
          attributes: finalAttributes,
          normalizedRequest: isolationScope.getScopeData().sdkProcessingMetadata.normalizedRequest,
          parentSampleRate: parseSampleRate(currentPropagationContext.dsc?.sample_rate),
        },
        currentPropagationContext.sampleRand,
      );

  const rootSpan = new SentrySpan({
    ...spanArguments,
    attributes: {
      [SEMANTIC_ATTRIBUTE_SENTRY_SOURCE]: 'custom',
      [SEMANTIC_ATTRIBUTE_SENTRY_SAMPLE_RATE]:
        sampleRate !== undefined && localSampleRateWasApplied ? sampleRate : undefined,
      ...finalAttributes,
    },
    sampled,
  });

  if (!sampled && client && !_isTracingSuppressed) {
    DEBUG_BUILD && debug.log('[Tracing] Discarding root span because its trace was not chosen to be sampled.');
    client.recordDroppedEvent('sample_rate', hasSpanStreamingEnabled(client) ? 'span' : 'transaction');
  }

  setCapturedScopesOnSpan(rootSpan, scope, isolationScope);

  if (client) {
    client.emit('spanStart', rootSpan);
  }