Best Of

To be honest I wish there were more first party documentation of featurescript period. I think I've found a sum total of 3 official tutorials in my browsing of the Onshape site and they all stop at what I would consider to be very barebones level features. My whole world revolves around sheet metal and frames too, which has been an uphill climb discovering all of the quirks of both of those feature sets and how they work.

this did it:

export function getWorkspaceUnits(definition is map) returns map
{

/*
    In precondition area:
    
    annotation { "Name" : "Length Unit", "UIHint" : UIHint.ALWAYS_HIDDEN }
        isLength(definition.lengthUnit, {
            (inch) : [-10000, 1.0, 10000],
            (meter) : 1,
            (centimeter) : 1,
            (millimeter) : 1,
            (foot) : 1,
            (yard) : 1 } as LengthBoundSpec);

    Usage:
    
    const wsu = getWorkspaceUnits(definition);
    var unitlessLength = length / wsu.unit;
    outputString = toString(roundToPrecision(unitlessLength,3))~" "~wsu.unitText;

*/

    var resultUnit = definition.lengthUnit;
    var unit;
    var unitText;

    if(tolerantEquals(resultUnit, 0.0254 * meter)){ unit = inch;       unitText = "inch";} 
    if(tolerantEquals(resultUnit,      1 * meter)){ unit = meter;      unitText = "meter";} 
    if(tolerantEquals(resultUnit,   0.01 * meter)){ unit = centimeter; unitText = "centimeter";} 
    if(tolerantEquals(resultUnit,  0.001 * meter)){ unit = millimeter; unitText = "millimeter";}

    var workspaceUnits = {"unit" : unit, "unitText" : unitText};
    
    return workspaceUnits;

}

Custom feature execution can't know about workspace units - otherwise, we'd have to regenerate the entire thing any time you change those. The workspace units are basically just for display. If custom feature code determines a part name, it can't depend on workspace units.

You could have your part-naming feature take units and a precision in the UI, and round to that?

There is a way you can get the current workspace units at the time you insert the feature. I learned this trick from Kevin:

https://cad.onshape.com/documents/e0c13dc3836c7dcba155622a/w/c3a138bc21a0284d4afbea62/e/a2290d1b855aec5d8f5af6f3…

Get the current default units when the feature is inserted. This input will default to 1 of whichever units the document is currently using at the time. Note that it only does it when you first insert the feature.

annotation { "Name" : "Invisible length", "UIHint" : UIHint.ALWAYS_HIDDEN }
            isLength(definition.lengthUnit, {
                            (inch) : [-10000, 1.0, 10000],
                            (meter) : 1,
                            (centimeter) : 1,
                            (millimeter) : 1,
                            (foot) : 1,
                            (yard) : 1 } as LengthBoundSpec);

and then, convert and round. Now that I'm looking at this next part, the switch statement might be redundant since the lengthUnit is already a resulting unit.

//get document units
    var resultUnit = switch (lengthUnit) {
            (inch) : inch,
            (meter) : meter,
            (centimeter) : centimeter,
            (millimeter) : millimeter,
            (foot) : foot,
            (yard) : yard,
        };

    var unitlessResult = distance / resultUnit;

    if (rounding)
    {
        distance = round(unitlessResult, roundingPrecision) * resultUnit;
    }

@martin_kopplow

I hacked myself a solution for now, but it could be better. Maybe one of the good FS coders will help me…

You can now use MCs, Arcs, Circles, Curves, and Lines. and it names the final sweep with the length

https://cad.onshape.com/documents/6661cf93ab8de38ee21084ba/w/b8355f5cf6f02bcaeade2553/e/26b8cb50d10f4b14394f2077