Speed up "check:cover" by using async exec (#1941)

resources/check-cover.js

@@ -10,30 +10,45 @@
 'use strict';
 
 const path = require('path');
-const { exec, writeFile, readdirRecursive } = require('./utils');
+const { exec, execAsync, writeFile, readdirRecursive } = require('./utils');
 
-const fullCoverage = {};
+getFullCoverage()
+  .then(fullCoverage =>
+    writeFile(
+      './coverage/flow/full-coverage.json',
+      JSON.stringify(fullCoverage),
+    ),
+  )
+  .catch(error => {
+    console.error(error.stack);
+    process.exit(1);
+  });
 
-exec('flow start --quiet');
-try {
-  exec('flow check', { stdio: 'inherit' });
+async function getFullCoverage() {
+  const fullCoverage = {};
 
-  // TODO: measure coverage for all files.
-  // ATM it takes too much time and test files missing types for chai & mocha
-  for (const filepath of readdirRecursive('./src', { ignoreDir: /^__.*__$/ })) {
-    if (filepath.endsWith('.js')) {
-      const fullpath = path.join('src/', filepath);
-      fullCoverage[fullpath] = getCoverage(fullpath);
-    }
+  exec('flow start --quiet');
+  try {
+    exec('flow check', { stdio: 'inherit' });
+
+    // TODO: measure coverage for all files. ATM  missing types for chai & mocha
+    const files = readdirRecursive('./src', { ignoreDir: /^__.*__$/ })
+      .filter(filepath => filepath.endsWith('.js'))
+      .map(filepath => path.join('src/', filepath));
+
+    await Promise.all(files.map(getCoverage)).then(covarageObjs => {
+      for (const coverage of covarageObjs) {
+        fullCoverage[coverage.path] = coverage;
+      }
+    });
+  } finally {
+    exec('flow stop --quiet');
   }
-} finally {
-  exec('flow stop --quiet');
+  return fullCoverage;
 }
 
-writeFile('./coverage/flow/full-coverage.json', JSON.stringify(fullCoverage));
-
-function getCoverage(filepath) {
-  const json = exec(`flow coverage --json ${filepath}`);
+async function getCoverage(filepath) {
+  const json = await execAsync(`flow coverage --json ${filepath}`);
   const flowExpressions = JSON.parse(json).expressions;
 
   const s = {};

resources/utils.js

@@ -10,6 +10,7 @@
 'use strict';
 
 const fs = require('fs');
+const util = require('util');
 const path = require('path');
 const childProcess = require('child_process');
 
@@ -19,8 +20,25 @@ function exec(command, options) {
     encoding: 'utf-8',
     ...options,
   });
-  // Remove trailing new line
-  return (output || '')
+  return removeTrailingNewLine(output);
+}
+
+const childProcessExec = util.promisify(childProcess.exec);
+async function execAsync(command, options) {
+  const output = await childProcessExec(command, {
+    maxBuffer: 10 * 1024 * 1024, // 10MB
+    encoding: 'utf-8',
+    ...options,
+  });
+  return removeTrailingNewLine(output.stdout);
+}
+
+function removeTrailingNewLine(str) {
+  if (str == null) {
+    return str;
+  }
+
+  return str
     .split('\n')
     .slice(0, -1)
     .join('\n');
@@ -87,6 +105,7 @@ function parseSemver(version) {
 
 module.exports = {
   exec,
+  execAsync,
   copyFile,
   writeFile,
   rmdirRecursive,