content: /**
   * Copyright (c) Facebook, Inc. and its affiliates.
   *
   * This source code is licensed under the MIT license found in the
   * LICENSE file in the root directory of this source tree.
   *
   * @flow
   */
  
  import React from 'react';
  import warning from 'shared/warning';
  import {getToStringValue, toString} from './ToStringValue';
  
  let didWarnSelectedSetOnOption = false;
  let didWarnInvalidChild = false;
  
  function flattenChildren(children) {
    let content = '';
  
    // Flatten children. We'll warn if they are invalid
    // during validateProps() which runs for hydration too.
    // Note that this would throw on non-element objects.
    // Elements are stringified (which is normally irrelevant
    // but matters for <fbt>).
    React.Children.forEach(children, function(child) {
      if (child == null) {
        return;
      }
      content += child;
      // Note: we don't warn about invalid children here.
      // Instead, this is done separately below so that
      // it happens during the hydration codepath too.
    });
  
    return content;
  }
  
  /**
   * Implements an <option> host component that warns when `selected` is set.
   */
  
  export function validateProps(element: Element, props: Object) {
    if (__DEV__) {
      // This mirrors the codepath above, but runs for hydration too.
      // Warn about invalid children here so that client and hydration are consistent.
      // TODO: this seems like it could cause a DEV-only throw for hydration
      // if children contains a non-element object. We should try to avoid that.
      if (typeof props.children === 'object' && props.children !== null) {
        React.Children.forEach(props.children, function(child) {
          if (child == null) {
            return;
          }
          if (typeof child === 'string' || typeof child === 'number') {
            return;
          }
          if (typeof child.type !== 'string') {
            return;
          }
          if (!didWarnInvalidChild) {
            didWarnInvalidChild = true;
            warning(
              false,
              'Only strings and numbers are supported as <option> children.',
            );
          }
        });
      }
  
      // TODO: Remove support for `selected` in <option>.
      if (props.selected != null && !didWarnSelectedSetOnOption) {
        warning(
          false,
          'Use the `defaultValue` or `value` props on <select> instead of ' +
            'setting `selected` on <option>.',
        );
        didWarnSelectedSetOnOption = true;
      }
    }
  }
  
  export function postMountWrapper(element: Element, props: Object) {
    // value="" should make a value attribute (#6219)
    if (props.value != null) {
      element.setAttribute('value', toString(getToStringValue(props.value)));
    }
  }
  
  export function getHostProps(element: Element, props: Object) {
    const hostProps = {children: undefined, ...props};
    const content = flattenChildren(props.children);
  
    if (content) {
      hostProps.children = content;
    }
  
    return hostProps;
  }
  