`File::create` fails on hidden files on Windows

[ChrisDenton]

Reported on discord, using OpenOptions::new().write(true).create(true).truncate(true).open(&path) will fail on Windows if the file is hidden. This also affects methods like File::create or fs::write that open the file the same way.

The reason for this is that we use CREATE_ALWAYS, which has strange behaviour:

If CREATE_ALWAYS and FILE_ATTRIBUTE_NORMAL are specified, CreateFile fails and sets the last error to ERROR_ACCESS_DENIED if the file exists and has the FILE_ATTRIBUTE_HIDDEN or FILE_ATTRIBUTE_SYSTEM attribute. To avoid the error, specify the same attributes as the existing file.

So to make it work the caller needs to match the requested attributes to the existing attributes at the time of opening.

Possible solution

It was suggested we could instead use OPEN_ALWAYS and then manually truncate the file using SetFileInformationByHandle to set the FILE_ALLOCATION_INFO to zero.

[bjorn3]

Manually truncating would require also clearing the alternate data streams too, right? And it would presumably stop erroring if another process still has the file open and instead corrupt the file fron the view of the other process.

[ChrisDenton]

No? The proposed solution would work the same was as TRUNCATE_EXISTING in the case where the file already exists. Which we use for .write(true).truncate(true).

[bjorn3]

Right, got confused with create_new.