Empty file can't be decrypted after setting password

[smss2022]

Steps to reproduce

1. Open vim
2. :set cm=xchacha20v2
3. :X
4. enter "test", confirm password
5. :w test
6. Quit vim
7. Open vim
8. :o test
9. vim doesn't correctly decrypt the file (i.e. display an empty file), but shows the binary content of the encrypted file.

Expected behaviour

vim should be able to create an encrypted empty template i.e. a file that normal users could edit and save, without having to think about encryption technicalities or editing their vimrc files.

Version of Vim

VIM - Vi IMproved 9.2 (2026 Feb 14, compiled Feb 14 2026 12:17:29)

Environment

Operating system: Windows 11 [Version 10.0.22631.6199]
Shell: Powershell 5.1.22621.613

Logs and stack traces

[smss2022]

Creating an unencrypted empty file, saving it, and reopening it works as intended. Setting a password to that file and trying to reopen it afterwards encounters the same bug i.e. the order of operations (encrypt then save as file, or save file and then encrypt) doesn't matter.

[smss2022]

Encryption method doesn't matter. Even if step 2 (i.e. choosing xchacha20v2) is omitted, the empty file encrypted with the default method (blowfish2) will not be properly decrypted upon reopening, but will show binary content instead.