Function createChildOrRootSpan

packages/core/src/tracing/trace.ts:350–453

({
  parentSpan,
  spanArguments,
  forceTransaction,
  scope,
}: {
  parentSpan: SentrySpan | undefined;
  spanArguments: SentrySpanArguments;
  forceTransaction?: boolean;
  scope: Scope;
})

}

function createChildOrRootSpan({
  parentSpan,
  spanArguments,
  forceTransaction,
  scope,
}: {
  parentSpan: SentrySpan | undefined;
  spanArguments: SentrySpanArguments;
  forceTransaction?: boolean;
  scope: Scope;
}): Span {
  const isolationScope = getIsolationScope();

  if (!hasSpansEnabled()) {
    const scopePropagationContext = { ...isolationScope.getPropagationContext(), ...scope.getPropagationContext() };
    const traceId = parentSpan ? parentSpan.spanContext().traceId : scopePropagationContext.traceId;

    // The placeholder is a thin marker; it carries no sampling decision or DSC. Both are read from
    // the scope: the sampling decision in `getTraceData`, the DSC in `getDynamicSamplingContextFromSpan`.
    const span = new SentryNonRecordingSpan({ traceId });

    // Nested placeholders link to their parent so `getRootSpan` resolves to the root placeholder,
    // whose captured scope is the source of truth. Root/forced placeholders are their own root.
    if (parentSpan && !forceTransaction) {
      addChildSpanToSpan(parentSpan, span);
    }

    // Capture scopes so consumers (e.g. SentryTraceProvider) can read them and so the DSC can be
    // resolved from the scope by `getDynamicSamplingContextFromSpan`. Consistent with `startIdleSpan`.
    setCapturedScopesOnSpan(span, scope, isolationScope);

    return span;
  }

  const client = getClient();
  if (_shouldIgnoreStreamedSpan(client, spanArguments)) {
    if (!isTracingSuppressed(scope)) {
      // if tracing is actively suppressed (Sentry.suppressTracing(...)),
      // we don't want to record a client outcome for the ignored span
      client?.recordDroppedEvent('ignored', 'span');
    }

    const ignoredSpan = new SentryNonRecordingSpan({
      dropReason: 'ignored',
      traceId: parentSpan?.spanContext().traceId ?? scope.getPropagationContext().traceId,
    });
    setCapturedScopesOnSpan(ignoredSpan, scope, isolationScope);

    return ignoredSpan;
  }

  let span: Span;
  if (parentSpan && !forceTransaction) {
    span = _startChildSpan(parentSpan, scope, spanArguments, isolationScope);
    addChildSpanToSpan(parentSpan, span);
  } else if (parentSpan) {
    // If we forced a transaction but have a parent span, make sure to continue from the parent span, not the scope
    const dsc = getDynamicSamplingContextFromSpan(parentSpan);