Wrong "Insufficient Disk Space"

[RaphaelMarinier]

Bug description

Audacity can refuse saving a project claiming "Insufficient Disk Space", while there is ample disk space on the target filesystem.

Steps to reproduce

1. Have a root filesystem / with low disk space.
2. Mount another filesystem with plenty of available disk space (e.g. external drive) to /run/media/user/disk_id (the number of components matters, see the additional context section)
3. Try to save a large audacity project (bigger than the available space on /, but smaller than the available space on /run/media/user/disk_id) to /run/media/user/disk_id/my_project.aup3.

Expected behavior

Audacity saves the project to /run/media/user/disk_id/my_project.aup3, since the fs mounted on /run/media/user/disk_id has enough disk space.

Actual behavior

Audacity refuses to save the project with error:

The project size exceeds the available free space on the target disk.
Please select a different disk with more free space

(BTW, it would be great to have the error message show the number of bytes it intends to write, and number of bytes available)

Audacity Version

stable version (from a Linux repository)

Operating system

Linux

Additional context

The bug is that ProjectFileManager::DoSave checks the available disk space with
wxGetDiskSpace(FileNames::AbbreviatePath(fileName), NULL, &freeSpace) (here).
This checks the available disk space on an abbreviatedpath of the target file. Abbreviating the path (i.e. keeping only 3 components of it) can cross filesystem boundaries on Linux and lead to returning the available disk space for the wrong filesystem.