For example, https://phabricator.services.mozilla.com/D37457

With --stdin-filepath, Prettier still attempts to look for a configuration file in the directory containing the specified "virtual" file path. With file renames or usual file moves, this problem doesn't manifest itself since the parent directory still exists. However, when the whole original directory is moved or doesn't exist anymore, Prettier fails internally. This looks like a bug inside Prettier and confirmed by the returned code 2.

I've attempted to work around this by forcing Prettier to not look for configuration files, with a combination of --config-precedence and --config params, with no success. Prettier seems to either ignore those or simply always check for a configuration file regardless of those params, as long as --stdin-filepath is passed, in the directory "containing" this "virtual" file path.

We can however also work around this by checking if the "virtual" file path for stdin actually exists or not. This seems to fix the problem and Prettier doesn't fail internally anymore with status code 2, and the merge completes successfully.

https://hg.mozilla.org/mozilla-central/rev/ec2818ee17f7