File on Projected File System is corrupted after being edited in MS Visual Studio

Oleg T 6

Hello,
I'm working on a project that uses ProjFS.

Turns out, if you project a virtual file to the filesystem, then open it in Microsoft Visual Studio, edit and save it, and then revert it back to the original virtual file using PrjDeleteFile, the file ends up in a bad state: it is shown when listing the directory (as expected), but when you try to open it, Windows says it doesn't exist. After that the file is stuck in this corrupted state forever: it cannot be opened or deleted (until you restart the computer).
I think it has to do something with how MS VS saves files (using temporary files and renaming) because if you do the same steps using Notepad or Visual Studio Code instead of Microsoft Visual Studio, "PrjDeleteFile" successfully reverts it back to its original state, and it can be edited again.
I tried Microsoft Visual Studio Community 2019, on Windows 10, 20H2 (build 19042.1110), as well as Microsoft Visual Studio Professional 2017, Windows 10, 1909 (build 18363.1679), the behavior is just the same.
I've made a simple reproducing app: it projects a virtual file of zero length in C:\Temp\Virt1\temp, then if you edit it in MS VS and revert the file back (pressing <enter> in the app), the file becomes corrupted.
Here's the link to it: https://github.com/lightln2/ProjFs-File-Corruption

Viorel 112.5K Reputation points

2021-07-31T14:12:00.57+00:00

The problem was not reproduced using Windows 10 (21H1, 19043.1110) and Visual Studio Enterprise 2019 (16.10.4).
Oleg T 6 Reputation points

2021-07-31T16:09:17.847+00:00

Hi Viorel,
thank you for the quick reply!
I tried on Windows 10, 21H1, and unfortunately, it still fails.
Here you can see video recording: https://youtu.be/AIYezU336lk

Is it possible that you tried it on a virtual machine with Windows, while I'm using physical desktop / laptop?
Viorel 112.5K Reputation points

2021-07-31T16:51:39.807+00:00

I use a normal Windows, no Virtual Machine.

Before experimenting, did you try closing all of programs and file managers that maybe watch the virtual folder (excepting Visual Studio)?
Oleg T 6 Reputation points

2021-07-31T17:10:35.637+00:00

Yes, I tried this, too (also temporarily disbaling antivirus),
on three different computers with three different Windows 10 versions, on both SSD and HDD - the problem happens no matter what
Xiaopo Yang - MSFT 11,496 Reputation points Microsoft Vendor

2021-08-02T07:08:34.187+00:00

I also cannot reproduce it.
Can you use CMD or File Explorer to show the directory? It should be nothing. And after PrjDeleteFile, It is unreasonable to continue to edit the file on the local file system. The notepad and devenv have consistent behavior in my computer.
Oleg T 6 Reputation points

2021-08-02T08:19:07.59+00:00
Hi Xiaopo Yang, thank you for the reply!

This is what Dir says (afterPrjDeleteFile was called):

08/02/2021 11:04 AM <DIR> . 08/02/2021 11:04 AM <DIR> .. 08/02/2021 11:07 AM 0 test 1 File(s) 0 bytes 2 Dir(s) 39,400,001,536 bytes free c:\temp\Virt1>type test The system cannot find the file specified.

Here is what File Explorer shows:

And after PrjDeleteFile, It is unreasonable to continue to edit the file

Why? As documentation says, this is what you do to revert the file back to virtual item:

If the item is still in the provider's backing store, deleting it from the local file system changes it to a virtual item
Xiaopo Yang - MSFT 11,496 Reputation points Microsoft Vendor

2021-08-03T02:23:25.267+00:00

After PrjDeleteFile, the file should be a virtual item residing in Projected File System and if the item is still in the provider's backing store, changing the file doesn‘t influence the virtual item.
It's bothersome to say the notepad and devenv have consistent behavior, after PrjDeleteFile notepad and devenv are capable of editing the local file , in my computer. Incidentally, I found the program doesn’t save the file data with PrjDeleteFile.