ensureCompatibility.js

import { isSupported } from 'caniuse-api';
import selectorParser from 'postcss-selector-parser';

const simpleSelectorRe = /^#?[-._a-z0-9 ]+$/i;

const cssSel2 = 'css-sel2';
const cssSel3 = 'css-sel3';
const cssGencontent = 'css-gencontent';
const cssFirstLetter = 'css-first-letter';
const cssFirstLine = 'css-first-line';
const cssInOutOfRange = 'css-in-out-of-range';

export const pseudoElements = {
  ':active': cssSel2,
  ':after': cssGencontent,
  ':before': cssGencontent,
  ':checked': cssSel3,
  ':default': 'css-default-pseudo',
  ':dir': 'css-dir-pseudo',
  ':disabled': cssSel3,
  ':empty': cssSel3,
  ':enabled': cssSel3,
  ':first-child': cssSel2,
  ':first-letter': cssFirstLetter,
  ':first-line': cssFirstLine,
  ':first-of-type': cssSel3,
  ':focus': cssSel2,
  ':focus-within': 'css-focus-within',
  ':focus-visible': 'css-focus-visible',
  ':has': 'css-has',
  ':hover': cssSel2,
  ':in-range': cssInOutOfRange,
  ':indeterminate': 'css-indeterminate-pseudo',
  ':lang': cssSel2,
  ':last-child': cssSel3,
  ':last-of-type': cssSel3,
  ':matches': 'css-matches-pseudo',
  ':not': cssSel3,
  ':nth-child': cssSel3,
  ':nth-last-child': cssSel3,
  ':nth-last-of-type': cssSel3,
  ':nth-of-type': cssSel3,
  ':only-child': cssSel3,
  ':only-of-type': cssSel3,
  ':optional': 'css-optional-pseudo',
  ':out-of-range': cssInOutOfRange,
  ':placeholder-shown': 'css-placeholder-shown',
  ':root': cssSel3,
  ':target': cssSel3,
  '::after': cssGencontent,
  '::backdrop': 'dialog',
  '::before': cssGencontent,
  '::first-letter': cssFirstLetter,
  '::first-line': cssFirstLine,
  '::marker': 'css-marker-pseudo',
  '::placeholder': 'css-placeholder',
  '::selection': 'css-selection',
};

function isCssMixin(selector) {
  return selector[selector.length - 1] === ':';
}

function isHostPseudoClass(selector) {
  return selector.includes(':host');
}

const isSupportedCache = {};

// Move to util in future
function isSupportedCached(feature, browsers) {
  const key = JSON.stringify({ feature, browsers });
  let result = isSupportedCache[key];

  if (!result) {
    result = isSupported(feature, browsers);
    isSupportedCache[key] = result;
  }

  return result;
}

export default function ensureCompatibility(
  selectors,
  browsers,
  compatibilityCache
) {
  // Should not merge mixins
  if (selectors.some(isCssMixin)) {
    return false;
  }

  // Should not merge :host selector https://github.com/angular/angular-cli/issues/18672
  if (selectors.some(isHostPseudoClass)) {
    return false;
  }
  return selectors.every((selector) => {
    if (simpleSelectorRe.test(selector)) {
      return true;
    }
    if (compatibilityCache && selector in compatibilityCache) {
      return compatibilityCache[selector];
    }
    let compatible = true;
    selectorParser((ast) => {
      ast.walk((node) => {
        const { type, value } = node;
        if (type === 'pseudo') {
          const entry = pseudoElements[value];
          if (entry && compatible) {
            compatible = isSupportedCached(entry, browsers);
          }
        }
        if (type === 'combinator') {
          if (~value.indexOf('~')) {
            compatible = isSupportedCached(cssSel3, browsers);
          }
          if (~value.indexOf('>') || ~value.indexOf('+')) {
            compatible = isSupportedCached(cssSel2, browsers);
          }
        }
        if (type === 'attribute' && node.attribute) {
          // [foo]
          if (!node.operator) {
            compatible = isSupportedCached(cssSel2, browsers);
          }

          if (value) {
            // [foo="bar"], [foo~="bar"], [foo|="bar"]
            if (~['=', '~=', '|='].indexOf(node.operator)) {
              compatible = isSupportedCached(cssSel2, browsers);
            }
            // [foo^="bar"], [foo$="bar"], [foo*="bar"]
            if (~['^=', '$=', '*='].indexOf(node.operator)) {
              compatible = isSupportedCached(cssSel3, browsers);
            }
          }

          // [foo="bar" i]
          if (node.insensitive) {
            compatible = isSupportedCached('css-case-insensitive', browsers);
          }
        }
        if (!compatible) {
          // If this node was not compatible,
          // break out early from walking the rest
          return false;
        }
      });
    }).processSync(selector);
    if (compatibilityCache) {
      compatibilityCache[selector] = compatible;
    }
    return compatible;
  });
}