Corrupted functions.php file after editing in built-in theme editor

[SergeyBiryukov]

Got ​at least two reports of the following scenario.

When editing the functions.php file of a theme, WordPress says: "Unable to communicate back with site to check for fatal errors, so the PHP change was reverted." However, the reverted file has 0 bytes length, and has to be recovered from a backup copy.

From what I can see, this can only happen in two cases:

• file_get_contents() could not properly read the file contents.
• The file is writable and fwrite() succeeded, but ​file_put_contents() did not.

Don't have any more details at this point, created the ticket as a reference for investigation.

[muhammedswalihct]

I am also facing this exact same issue. Lost the entire functions.php file due to this.