getChangedFiles.js

// @flow

import os from 'os';
import isCI from 'is-ci';

import Git from './Git';

/**
 * This function tries to determine what changes are relevant at the moment.
 * Relevant changes are unstaged/uncommited files, modified files on the branch
 * from master or changes in the last commit as a fallback. It expects default
 * branch to be master. This is how it works internally:
 *
 * First it executes these commands:
 *
 *     git ls-files --others --exclude-standard               # untracked files
 *       +
 *     git --no-pager diff --name-only HEAD                   # uncommited but staged files
 *       +
 *     git --no-pager diff --name-only origin/master...HEAD   # modified files on the feature branch (3 dots are important)
 *
 * Fallback for master or new branches of no result was returned:
 *
 *     git --no-pager diff --name-only HEAD^ HEAD             # latest commit (doesn't work with only one commit in Git history)
 *
 * For more details: https://git-scm.com/docs/git-diff
 */
export default function getChangedFiles(): $ReadOnlyArray<string> {
  const uncommittedChanges = Git.getUntrackedFiles().concat(
    Git.getWorktreeChangedFiles(),
  );

  // It's OK to run tests on uncommitted changes locally but it's unexpected
  // in CI because it indicates that CI generated something which is not
  // expected (tests runner would be confused and it would try to test
  // the newly generated files).
  if (isCI === true && uncommittedChanges.length > 0) {
    // eslint-disable-next-line no-console
    console.error(
      `ERROR: There are some uncommitted changes in the working tree:

${uncommittedChanges.join(os.EOL)}

This usually means that CI generated some changes (for example during installation of dependencies) which is unexpected. Please try to fix it locally and commit the newly generated files.`,
    );
    process.exit(1);
  }

  return uncommittedChanges.length > 0
    ? uncommittedChanges
    : Git.getLastCommitChanges();
}