react-native-devtools-frontend/scripts/build/ninja/copy-files.js

// Copyright 2020 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
const fs = require('fs');
const path = require('path');
const {writeIfChanged} = require('./write-if-changed.js');
const [, , src, dest, files] = process.argv;

for (const file of files.split(',')) {
  const srcPath = path.join(src, file);
  const destPath = path.join(dest, file);

  // If there's a file there from a previous build, unlink it first. This
  // is because the file in that location might be a hardlinked file, and
  // overwriting it doesn't change the fact that it's hardlinked.
  const srcContents = fs.readFileSync(srcPath);
  if (fileExists(destPath)) {
    // Check contents, return early if match
    const destContents = fs.readFileSync(destPath);
    if (srcContents.equals(destContents)) {
      continue;
    }
  }

  // Force a write to the target filesystem, since by default the ninja
  // toolchain will create a hardlink, which in turn reflects changes in
  // gen and resources/inspector back to //front_end.
  writeIfChanged(destPath, srcContents);
}

/**
 * Case sensitive implementation of a file look up.
 */
function fileExists(filePath) {
  const dir = path.dirname(filePath);
  const files = fs.readdirSync(dir);
  return files.includes(path.basename(filePath));
}