@material-ui/core/es/styles/createSpacing.js

import { createUnarySpacing } from '@material-ui/system';
let warnOnce;
export default function createSpacing(spacingInput = 8) {
  // Already transformed.
  if (spacingInput.mui) {
    return spacingInput;
  } // Material Design layouts are visually balanced. Most measurements align to an 8dp grid applied, which aligns both spacing and the overall layout.
  // Smaller components, such as icons and type, can align to a 4dp grid.
  // https://material.io/design/layout/understanding-layout.html#usage


  const transform = createUnarySpacing({
    spacing: spacingInput
  });

  const spacing = (...args) => {
    if (process.env.NODE_ENV !== 'production') {
      if (!(args.length <= 4)) {
        console.error(`Material-UI: Too many arguments provided, expected between 0 and 4, got ${args.length}`);
      }
    }

    if (args.length === 0) {
      return transform(1);
    }

    if (args.length === 1) {
      return transform(args[0]);
    }

    return args.map(argument => {
      if (typeof argument === 'string') {
        return argument;
      }

      const output = transform(argument);
      return typeof output === 'number' ? `${output}px` : output;
    }).join(' ');
  }; // Backward compatibility, to remove in v5.


  Object.defineProperty(spacing, 'unit', {
    get: () => {
      if (process.env.NODE_ENV !== 'production') {
        if (!warnOnce || process.env.NODE_ENV === 'test') {
          console.error(['Material-UI: theme.spacing.unit usage has been deprecated.', 'It will be removed in v5.', 'You can replace `theme.spacing.unit * y` with `theme.spacing(y)`.', '', 'You can use the `https://github.com/mui-org/material-ui/tree/master/packages/material-ui-codemod/README.md#theme-spacing-api` migration helper to make the process smoother.'].join('\n'));
        }

        warnOnce = true;
      }

      return spacingInput;
    }
  });
  spacing.mui = true;
  return spacing;
}