tox -p without number should enable auto mode

[ssbarnea]

It would a good improvement in user experience if when adding just -p, tox would run in parallel mode, like it does not with tox -p auto. This would save 5 keystrokes when calling tox.

I think that auto is likely what most people want when they want to run in parallel, so why to ask the to type more for getting it.

[awecx]

This would be consistent with makefile -j where, if no argument is given, make would select a number of parallel recipes to build, by itself.

[JulienPalard]

This would be consistent with makefile -j where, if no argument is given, would select a number of parallel recipes to build itself.

I'm not sure for every make implemn, but quoting the GNU make manpage:

If the -j option is given without an argument, make will not limit the number of jobs that can run simultaneously.

Which looks more like all than auto.

(This typically make make -j a bit violent when compiling cpython.)

I'd say all is not a sane default, and defaulting to auto looks a better choice.

While thinking about it, I bet (it's only a bet, so don't mind me) auto can be faster than all as both run the same quantity of instructions, but in the all case there may be more context switches (or worse, swapping).

[gaborbernat]

Feel free to open a PR against master and fix it. My available efforts at the moment are aimed at fixing this as part of #1394, but that probably will take a while (ETA September).

[gaborbernat]

Hello, this now has been released via https://pypi.org/project/tox/3.15.0/