Repository: facebook/jest
File: packages/jest-create-cache-key-function/src/index.ts (TypeScript)

Code before:
      .update('\0', 'utf8')
      .update(sourceText)
      .update('\0', 'utf8')
      .update(config.rootDir ? relative(config.rootDir, sourcePath) : '')
      .update('\0', 'utf8')
      .update(instrument ? 'instrument' : '')
      .digest('hex')
      .substring(0, 32);
  };
}

/**
 * Computes the cache key given  a collection of files and values.  This limits
 * the output with a provided length.
 * @param files list of files to read
 * @param values list of values to add to the computation
 * @param length length of the resulting key defaults to 16 on win32 and 32 elsewhere
 * @returns {string} the global cache key
 */
export default function createCacheKey(
  files: Array<string> = [],
  values: Array<string> = [],
  length?: number,
): GetCacheKeyFunction {
  const theLength = length ?? (process.platform === 'win32' ? 16 : 32);
  return getCacheKeyFunction(getGlobalCacheKey(files, values, theLength));
}


Review comment (performance):
```suggestion
  return getCacheKeyFunction(getGlobalCacheKey(files, values, length));
```

Code after:
/**
 * Copyright (c) Meta Platforms, Inc. and affiliates.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 *
 */

import {createHash} from 'crypto';
// eslint-disable-next-line no-restricted-imports
import {readFileSync} from 'fs';
import {relative} from 'path';
import type {Config} from '@jest/types';

type OldCacheKeyOptions = {
  config: Config.ProjectConfig;
  instrument: boolean;
};

// Should mirror `import('@jest/transform').TransformOptions`
type NewCacheKeyOptions = {
  config: Config.ProjectConfig;
  configString: string;
  instrument: boolean;
};

type OldGetCacheKeyFunction = (
  fileData: string,
  filePath: string,
  configStr: string,
  options: OldCacheKeyOptions,
) => string;

// Should mirror `import('@jest/transform').Transformer['getCacheKey']`
type NewGetCacheKeyFunction = (
  sourceText: string,
  sourcePath: string,
  options: NewCacheKeyOptions,
) => string;

type GetCacheKeyFunction = OldGetCacheKeyFunction | NewGetCacheKeyFunction;

function getGlobalCacheKey(
  files: Array<string>,
  values: Array<string>,
  length: number,
) {
  return [
    process.env.NODE_ENV,
    process.env.BABEL_ENV,
    ...values,
    ...files.map((file: string) => readFileSync(file)),
  ]
    .reduce(
      (hash, chunk) => hash.update('\0', 'utf8').update(chunk || ''),
      createHash('sha1'),
    )
    .digest('hex')
    .substring(0, length);
}

function getCacheKeyFunction(
  globalCacheKey: string,
  length: number,
): GetCacheKeyFunction {
  return (sourceText, sourcePath, configString, options) => {
    // Jest 27 passes a single options bag which contains `configString` rather than as a separate argument.
    // We can hide that API difference, though, so this module is usable for both jest@<27 and jest@>=27
    const inferredOptions = options || configString;
    const {config, instrument} = inferredOptions;

    return createHash('sha1')
      .update(globalCacheKey)
      .update('\0', 'utf8')
      .update(sourceText)
      .update('\0', 'utf8')
      .update(config.rootDir ? relative(config.rootDir, sourcePath) : '')
      .update('\0', 'utf8')
      .update(instrument ? 'instrument' : '')
      .digest('hex')
      .substring(0, length);
  };
}

/**
 * Returns a function that can be used to generate cache keys based on source code of provided files and provided values.
 *
 * @param files - Array of absolute paths to files whose code should be accounted for when generating cache key
 * @param values - Array of string values that should be accounted for when generating cache key
 * @param length - Length of the resulting key. The default is `32`, or `16` on Windows.
 * @returns A function that can be used to generate cache keys.
 */
export default function createCacheKey(
  files: Array<string> = [],
  values: Array<string> = [],
  length = process.platform === 'win32' ? 16 : 32,
): GetCacheKeyFunction {
  return getCacheKeyFunction(getGlobalCacheKey(files, values, length), length);
}