about XDG_RUNTIME_DIR

[René J.V. Bertin]

Hi,

I'd like to reach as many users and developers as possible, hence I'm asking here:

Freedesktop/XDG-compliant applications may use a user-specific location for runtime "stuff" like sockets. On Linux, this location usually is something like /run/user/uid. It is typically defined globally through the XDG_RUNTIME_DIR env. variable, with a fallback if that variable doesn't exist.

How does MacPorts handle this, is there a consensus? Or are applications and "frameworks" left to determine their own fallback value because XDG_RUNTIME_DIR will typically NOT be set? The only beginning of an answer I have for now is the presence of a few ~/.cache/keyring-XXXXX directories, which may correspond to the similarly named keyring directories in /run/user/uid on my Linux rig.

Context: Qt5's QStandardPaths::RuntimeLocation return value. It defaults to ~/Library/Application Support, which I think is fine for "native mode" but not for an XDG-compliant mode.
Alternatives I see:
- $TMPDIR/runtime-username (calculated using the QSP RuntimeLocation code used on other Unix hosts)
- ~/.cache (to align with what Gnome *may* use).

I tend to prefer the 1st alternative to stick closest to what happens on Linux, but only if Qt5-based and non-Qt5-based applications and libraries need NOT agree on the location.

Thoughts?
Thanks,
René