keyvault packages mutate passed spanOptions

[xirzec]

• Package Name: keyvault-certificates, keyvault-keys, keyvault-secrets
• Package Version: 4.0.0-preview.6

Describe the bug

Operations can take a manual tracing span like this

const result = await client.createKey(keyName, "EC", {
      requestOptions: {
        spanOptions: {
          parent: rootSpan
        }
      }
    });

The problem arises that under the covers these libraries mutate spanOptions inside a private createSpan helper:

  /**
   * Creates a span using the tracer that was set by the user
   * @param methodName The name of the method for which the span is being created.
   * @param requestOptions The options for the underlying http request. This will be
   * updated to use the newly created span as the "parent" so that any new spans created
   * after this point gets the right parent.
   */
  private createSpan(methodName: string, requestOptions?: RequestOptionsBase): Span {
    const tracer = TracerProxy.getTracer();
    const options = requestOptions || {};
    const span = tracer.startSpan(methodName, options.spanOptions);
    if (
      tracer.pluginType !== SupportedPlugins.NOOP &&
      (options.spanOptions && options.spanOptions.parent)
    ) {
      options.spanOptions = { ...options.spanOptions, parent: span };
    }
    return span;
  }
}

The issue being that if a user does two operations with a re-used options bag (expecting reasonably that their options would not be mutated), the tracing graph will be incorrect:

const requestOptions = {
  spanOptions: {
    parent: rootSpan
  }
};
const result = await client.createKey(keyName, "AB", { requestOptions});
const result2 = await client.createKey(keyName, "CD", { requestOptions});

The expectation is that the above operations would have the same parent root span, but currently the second createKey would be parented under the first.