From https://help.gnome.org/users/mousetweaks/stable/mouse-a11y-functions-description.html.en#mouse-a11y-dwell-description "There are users that cannot use any hardware button. By activating the Dwell Click, they can have the mouse perform the various clicks without pressing any mouse button. The click types that can be performed are: single primary click, double click, drag click and secondary click. ... Each time the pointer stops moving, a dwell click is initiated." The core is simple to implement, the tricky bit is the complex configuration options and the feedback. From the above link "To give feedback to the user, mousetweaks will fill the arrow of the pointer with another color while it is counting down the time before the click completion kicks in.". This is essentially impossible in libinput without flagging the event. Maybe dwell click is better off as compositor option then?
I would say this is a compositor level thing. libinput isn't missing anything to implement it
another argument to implement this in the compositor: libinput only sees movement on a per-device level, but we must not trigger a dwell click if any other device is moving the pointer. we don't know in libinput if an event will move the pointer (or which pointer, if multiple wl_seats are present).
Closing this bug, won't be implemented in libinput. See the above comments.
Mutter bug is at: https://bugzilla.gnome.org/show_bug.cgi?id=747515
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