Instrument vite build using nyc

instrument-test-build.js

// @ts-check

const fs = require('fs');
const path = require('path');
const os = require('os');
var { spawn } = require('child_process');
const systemCpuCores = os.cpus();

const pathToArtifacts = path.join(__dirname, '..', 'build', 'assets');
const processes = systemCpuCores.length > 1 ? systemCpuCores.length - 1 : 1;
const files = fs.readdirSync(pathToArtifacts);

const filesToInstrument = files
  .map((el) => {
    const meta = path.parse(el);
    const shouldProcess =
      meta.ext === '.js' &&
      !meta.name.startsWith('vendor') &&
      !meta.name.includes('.min.');
      
    const fullPath = path.join(pathToArtifacts, el);

    return shouldProcess
      ? {
          name: el,
          fullPath,
          size: fs.statSync(fullPath).size,
        }
      : null;
  })
  .filter((e) => e !== null)
  .sort((a, b) => {
    return b.size - a.size;
  });

const poolQueue = new Array(processes).fill(null).map((_) => []);

let poolIndex = 0;
filesToInstrument.forEach((file) => {
  poolQueue[poolIndex].push(file.fullPath);
  poolIndex++;
  if (poolIndex === processes) {
    poolIndex = 0;
  }
});

async function processInThread(items) {
  for (let file of items) {
    await new Promise((resolve, reject) => {
      const child = spawn('node', [path.join(__dirname, 'worker__instrument-file.js'), file], {
        env: {
          ...process.env,
          NODE_OPTIONS: '--max-old-space-size=8096',
        },
      });
      child.stderr.on('data', (data) => {
        console.error(Buffer.from(data).toString());
      });
      child.on('close', (code) => {
        if (code !== 0) {
          reject(code);
        } else {
          resolve('');
        }
      });
    });
  }
}

async function processFiles(chunks) {
  const promises = chunks.map((files) => {
    return processInThread(files);
  });
  await Promise.all(promises);
}

console.time('instrument');
processFiles(poolQueue)
  .catch((e) => {
    console.error(e);
  })
  .then(() => {
    console.timeEnd('instrument');
  });

worker__instrument-file.js

// @ts-check

const filePath = process.argv[2];
const babel = require('@babel/core');
const babelPluginIstanbul = require('babel-plugin-istanbul');
const fs = require('fs');

async function transformFile(fullFileName) {
  var result = await babel.transformFileAsync(fullFileName, {
    babelrc: false,
    compact: false,
    sourceMaps: true,
    configFile: false,
    inputSourceMap: JSON.parse(fs.readFileSync(fullFileName + '.map', 'utf8')),
    plugins: [
      [
        babelPluginIstanbul,
        {
          include: ['**/*.js'],
        },
      ],
    ],
  });
  fs.writeFileSync(fullFileName, result?.code ?? '', 'utf8');
  fs.writeFileSync(fullFileName + '.map', JSON.stringify(result?.map), 'utf8');
}

transformFile(filePath);