xpra subcommands should assume current instance where possible

[karlkleinpaste]

$ xpra detach
xpra initialization error:
 there are multiple servers running, please specify

When xpra is run from an xpra-driven window, it should be reasonable to assume that the server in question is $DISPLAY, yes? Is there a good reason not to default to $DISPLAY?

Many subcommands could assume this, like xpra screenshot xyz.png. Perhaps something more precise and xpra-specific than $DISPLAY is in order, like maybe XPRA_SERVER_SOCKET.

When there's a genuine ambiguity, notably when no $DISPLAY exists, sure, xpra should ask for specifics.

[totaam]

Done in the commit above for most subcommands: info, id, shell, qrcode, version, detach, show-menu, show-session-info, etc..
This uses XPRA_SERVER_SOCKET because, as you pointed out, that's much more likely to be correct.

[normanr]

I noticed that control and print both still require the DISPLAY argument, but I discovered that it's allowed to be empty :-)

[totaam]

I noticed that control and print both still require the DISPLAY argument, but I discovered that it's allowed to be empty :-)

Yes, we use positional arguments so it can't be removed completely but you can use an empty placeholder.