It is a bit hard to test this since we don't see it, so so far I have only a few comments:

1. We need an operator to select all/deselect all (with the expected shortcuts).
2. The other selection modes (box and lasso) could be super useful as well. Either as part of this patch or as a separate one.
3. I wonder we should have the Select Circle as a separate tool, or if this is the select circle (I'm at the moment more inclined to separate tools to be honest. The painting one you can worry about texture and whatnot, and we keep the circle one simpler).
4. In which case we may want to call this "Select Paint"? (to go along with Select Box, Select Lasso).
5. I think we need an option (for all selection tools) to pick between control-points or splines, until we can have them as separate selection modes (together with the root points).

PS: We will probably a notifier to show the updated selection in the viewport. But that can wait until we have proper support for
PPS: At the moment the .hidden_attribute is visible while I believe it shouldn't.

Note: I added two new icons to the icons file:

• ops.generic.select_paint
• ops.generic.select_line

They are in the Unused collection at the moment. The 'select paint' should be used for this tool.

For the records:

1. We need an operator to select all/deselect all (with the expected shortcuts).

Right. in this update I've added A, Alt-A and Crtl-I shortcuts for the relevant functions. It's fast, but apparently mesh sculpt mode uses a pie menu for this. I think it's okay to be more similar to edit mode now though.

2. The other selection modes (box and lasso) could be super useful as well. Either as part of this patch or as a separate one.

I looked into adding these, and it doesn't seem trivial, so I'd rather look into that with a separate patch.

3. I wonder we should have the Select Circle as a separate tool, or if this is the select circle...

After some more discussion, I think we decided that just selection paint was okay for now, right?

4. In which case we may want to call this "Select Paint"? (to go along with Select Box, Select Lasso).

No strong opinion about the name here, it's easy to change.

5. I think we need an option (for all selection tools) to pick between control-points or splines, until we can have them as separate selection modes (together with the root points).

Actually, thinking about this a bit more, I think starting with adding the selection modes might be the easiest and most intuitive solution, regardless of how the data is actually stored.

We had another round of discussions about this feature:

• Have only two selection domain/modes: control points and splines.
• The None is no longer a mode but the modes can both be turned off.
• Instead of using a toggle use Alt+1, Alt+2.
• When switching to a tool or selection operator automatically turn the previous used mode on.

Bug 1: If I have disabled one of the modes (e.g., control point mode) I cannot go back to it directly.

A. Press 2 to be in the splines mode.
B. Press Alt+2 to disable it.
C. Press 2 again, nothing happens.

(in order to re-able splines mode I need to first press 1 and then 2).

Bug 2: This should be also hidden if experimental Curve tools are disabled:

Just for the records we still need to hide the .selection_* attributes from the Spreadsheet Editor and the attributes panel in the Properties Editor.

Other than that the patch seems fine.

Note: I'm not totally convinced that the way we convert from control points to spline is the best (when user goes from 1 to 2). But we can adjust that once this lands in master. My original thought would be to set the spline to the highest value of any of the control points. Or the lower number even (it depends on what we settle when it comes to the boolean selection tools). I have a feeling that using the average as it is now is a bit strange when compared to the behaviour for the boolean selections (when going from 1 to 2 is fine, the other way around is fine).