Function checkSourcemapMappings

build-system/tasks/check-sourcemaps.js:107–152

* Performs a sanity check on the mappings field in the sourcemap file. * * Today, the first line of amp.js after resolving imports comes from * src/polyfills/array-includes.js. (The import chain is src/amp.js -> * src/polyfills/index.js -> src/polyfills/array-includes.js.) This sequence * chang

(sourcemapJson, map)

 * @param {string} map The map filepath to check
 */
function checkSourcemapMappings(sourcemapJson, map) {
  log('Inspecting', cyan('mappings'), 'in', cyan(map) + '...');
  if (!sourcemapJson.mappings) {
    log(red('ERROR:'), 'Could not find', cyan('mappings'));
    throw new Error('Could not find mappings array');
  }

  // See https://www.npmjs.com/package/sourcemap-codec#usage.
  const firstLineMapping = decode(sourcemapJson.mappings)[1][0];
  const [, sourceIndex = 0, sourceCodeLine = 0, sourceCodeColumn] =
    firstLineMapping;

  const firstLineFile = sourcemapJson.sources[sourceIndex];
  const contents = fs.readFileSync(firstLineFile, 'utf8').split('\n');
  const firstLineCode = contents[sourceCodeLine].slice(sourceCodeColumn);
  const helpMessage =
    'If this change is intentional, update the mapping related constants in ' +
    cyan('build-system/tasks/check-sourcemaps.js') +
    '.';

  // Mapping related constants
  const expectedFirstLine = map.includes('mjs')
    ? {
        file: 'src/polyfills/abort-controller.js',
        code: 'class AbortController {',
      }
    : {
        file: 'node_modules/@babel/runtime/helpers/esm/createClass.js',
        code: 'function _defineProperties(target, props) {',
      };

  if (firstLineFile != expectedFirstLine.file) {
    log(red('ERROR:'), 'Found mapping for incorrect file.');
    log('Actual:', cyan(firstLineFile));
    log('Expected:', cyan(expectedFirstLine.file));
    log(helpMessage);
    throw new Error('Found mapping for incorrect file');
  }
  if (firstLineCode != expectedFirstLine.code) {
    log(red('ERROR:'), 'Found mapping for incorrect code.');
    log('Actual:', cyan(firstLineCode));
    log('Expected:', cyan(expectedFirstLine.code));
    log(helpMessage);
    throw new Error('Found mapping for incorrect code');
  }
}

/**
 * @param {string} map The map filepath to check