Sketch block's `on` parameter should be allowed to be any expression

[jtran]

...not just a variable.

[jtran]

I think we need to cache the surface of every sketch block. Then, when we're executing a SketchBlock, if it's sketch mode, skip evaluating the arguments. In that case, we should only execute the body, and with the additional cached items, we shouldn't need to re-evaluate the arguments.

[max-mrgrsk]

is it related to this issue? #9271

[jtran]

No, #9271 is the ability to sketch on anything.

This issue is whether it needs to be in a separate KCL variable. Currently, if you try to do this:

sketch(on = -XY) { }

...it's an error because -XY isn't a variable; it's the negation expression. Similar thing for faces using faceOf().

The restriction was added as a simplification in:

• Sketch mode partial execution #9557