index.js

/* eslint-disable no-param-reassign */
import { createInstrumenter } from 'istanbul-lib-instrument';
import loaderUtils from 'loader-utils';
import validateOptions from 'schema-utils';
import convert from 'convert-source-map';
/* eslint-disable-line */
const schema = require('./options');


export default function instanbulInstrumentLoader(source, sourceMap) {
  /**
   * This is an unfortunate hack that lets us use fork-ts-checker-webpack-plugin
   * for a faster build, whilst also checking for 100% branch coverage with Istanbul.
   *
   * Based on: https://github.com/kulshekhar/ts-jest/pull/488
   *
   * When TypeScript transpiles, it introduces some logic branches outside of our
   * control, particularly where decorators are concerned.
   *
   * This is a thin wrapper around the istanbul-instrumenter-loader for Webpack,
   * which modifies the transpiled code and inserts Istanbul ignore statements
   * to ignore these branches.
   */
  if (source) {
    // Ignore decorators on methods and properties
    source = source.replace(/(tslib.+\.__decorate)/g, '/* istanbul ignore next */$1');
    // When constructor parameters have decorated properties (eg @inject), TS adds
    // a typeof branch check, which we don't want to instrument
    source = source.replace(/(typeof \(_\w\s*=)/g, '/* istanbul ignore next */$1');
    // ------------------------- END OF HACK -------------------------
  }
  const options = Object.assign({ produceSourceMap: true }, loaderUtils.getOptions(this));

  validateOptions(schema, options, {
    name: 'Istanbul Instrumenter Loader',
    baseDataPath: 'options',
  });

  let srcMap = sourceMap;
  // use inline source map, if any
  if (!srcMap) {
    const inlineSourceMap = convert.fromSource(source);
    if (inlineSourceMap) {
      srcMap = inlineSourceMap.sourcemap;
    }
  }

  const instrumenter = createInstrumenter(options);

  instrumenter.instrument(source, this.resourcePath, (error, instrumentedSource) => {
    this.callback(error, instrumentedSource, instrumenter.lastSourceMap());
  }, srcMap);
}