Unit-less parameters used as lengths read in the design's units (feature evaluation and parameter values; bare numbers stored in inputs stay mm); document.units checks what the geometry reads (Document::length_inputs) and writes the old unit (with it as the parameter's unit) into bare unit-less parameters that would move; cached results keyed on the design's units

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AS5Tn3xieewUSg3uxrMVdL

crates/doc/src/eval.rs

@@ -338,6 +338,7 @@ fn fingerprint(prev: u64, f: &Feature, vals: &BTreeMap<String, Value>, rolled_ba
     let mut h = std::collections::hash_map::DefaultHasher::new();
     prev.hash(&mut h);
     rolled_back.hash(&mut h);
+    vals.get(DESIGN_LEN).map(|v| v.v.to_bits()).hash(&mut h);
     serde_json::to_string(f).unwrap_or_default().hash(&mut h);
     for n in param_names(f) {
         n.hash(&mut h);
@@ -360,6 +361,7 @@ fn context_digest(doc: &Document, vals: &BTreeMap<String, Value>) -> u64 {
     for f in doc.features.iter().filter(|f| matches!(f.kind, FeatureKind::ConstructionPlane { .. })) {
         fingerprint(0, f, vals, false).hash(&mut h);
     }
+    doc.units.hash(&mut h);
     serde_json::to_string(&doc.sheet).unwrap_or_default().hash(&mut h);
     serde_json::to_string(&doc.plastic).unwrap_or_default().hash(&mut h);
     serde_json::to_string(&doc.components).unwrap_or_default().hash(&mut h);
@@ -429,7 +431,12 @@ impl Model {
 
     /// Re-evaluate the document, reusing results up to the first changed feature.
     pub fn evaluate(&mut self, doc: &Document) {
-        let (vals, perr) = doc.param_values();
+        let (mut vals, perr) = doc.param_values();
+        if let Some((Kind::Length, scale)) = expr::unit_info(doc.units.trim())
+            && scale != 1.0
+        {
+            vals.insert(DESIGN_LEN.into(), Value { v: scale, len: 0, ang: 0 });
+        }
         self.param_errors = perr;
         let mut prev_fp = 0u64;
         let mut state = self.empty.clone();
@@ -586,7 +593,18 @@ impl Model {
     }
 }
 
+/// Key of the design's length unit (mm per unit) among the values (no parameter can be named
+/// so).
+pub(crate) const DESIGN_LEN: &str = "\u{1}design_len";
+
+/// An expression's value. A length that comes out unit-less without being a bare number (a
+/// unit-less parameter used as a length) is in the design's units.
 fn val(vals: &BTreeMap<String, Value>, e: &str, k: Kind) -> Result<f64> {
+    let scale = vals.get(DESIGN_LEN).map(|x| x.v).unwrap_or(1.0);
+    if k == Kind::Length && scale != 1.0 && !expr::is_literal(e) {
+        let v = expr::eval_with(e, &|n| vals.get(n).copied().ok_or_else(|| DocError::Expr(format!("unknown parameter `{n}`"))))?;
+        return v.to_kind_in(k, expr::Defaults { len: scale, ..expr::Defaults::default() });
+    }
     Document::eval_in(vals, e, k)
 }
 

crates/doc/src/params.rs

@@ -338,6 +338,23 @@ impl Document {
         }
     }
 
+    /// Every length input of every feature as the geometry reads it (mm; a unit-less result is
+    /// in the design's units), for checking that an edit moves nothing.
+    pub fn length_inputs(&self) -> Vec<Option<f64>> {
+        let (vals, _) = self.param_values();
+        let scale = expr::unit_info(self.units.trim()).filter(|(k, _)| *k == Kind::Length).map(|(_, s)| s).unwrap_or(1.0);
+        let look = |n: &str| vals.get(n).copied().ok_or_else(|| DocError::Expr(format!("unknown parameter `{n}`")));
+        self.features
+            .iter()
+            .flat_map(|f| f.kind.inputs())
+            .filter(|(_, _, k)| *k == Kind::Length)
+            .map(|(_, e, _)| {
+                let d = if expr::is_literal(&e) { expr::Defaults::default() } else { expr::Defaults { len: scale, ..expr::Defaults::default() } };
+                expr::eval_with(&e, &look).and_then(|v| v.to_kind_in(Kind::Length, d)).ok()
+            })
+            .collect()
+    }
+
     pub fn change_param(&mut self, name: &str, expr_s: &str, unit: Option<&str>, comment: Option<&str>) -> Result<()> {
         let hit = self.features.iter().enumerate().find_map(|(i, f)| f.param_names.iter().position(|n| n == name).map(|k| (i, k)));
         let Some((i, k)) = hit else { return self.set_param(name, expr_s, unit, comment) };
@@ -529,7 +546,16 @@ impl Document {
         for f in &self.features {
             for (name, (_, e, k)) in f.param_names.iter().zip(f.kind.inputs()) {
                 if !name.is_empty() {
-                    v.push(ParamDef { name: name.clone(), expr: e, unit: unit_of(k).into() });
+                    // A bare number stored in an input is mm (the design's units are written in
+                    // when it is typed); anything else that comes out unit-less (a unit-less
+                    // parameter used as a length) is in the design's units.
+                    let unit = match k {
+                        Kind::Length if !expr::is_literal(&e) && expr::unit_info(self.units.trim()).is_some_and(|(k, _)| k == Kind::Length) => {
+                            self.units.trim().to_string()
+                        }
+                        _ => unit_of(k).to_string(),
+                    };
+                    v.push(ParamDef { name: name.clone(), expr: e, unit });
                 }
             }
         }

crates/engine/src/cmd/browser.rs

@@ -165,14 +165,17 @@ fn document_units(s: &mut Session, p: &Value) -> Result<Value> {
     if old == u {
         return Ok(json!({ "units": u, "kept": [] }));
     }
-    let (before, _) = s.doc.param_values();
+    // What the geometry reads: every feature's length inputs.
+    let before = s.doc.length_inputs();
     s.doc_mut().units = u.to_string();
     // Unit-less user parameters holding a bare number read it in the design's units where they
-    // stand for lengths. If any value moved, those numbers keep the old unit, written out.
-    let (after, _) = s.doc.param_values();
-    let moved = before.iter().any(|(k, b)| after.get(k).is_none_or(|a| (a.v - b.v).abs() > 1e-9 * b.v.abs().max(1.0)));
+    // stand for lengths. If any input moved, those numbers keep the old unit, written out.
+    let same = |a: &[Option<f64>]| {
+        a.iter().zip(&before).filter(|(x, y)| matches!((x, y), (Some(x), Some(y)) if (x - y).abs() <= 1e-9 * y.abs().max(1.0))).count()
+    };
+    let after = s.doc.length_inputs();
     let mut kept = Vec::new();
-    if moved {
+    if same(&after) < before.len() {
         let bare: Vec<(String, String)> = s
             .doc
             .params
@@ -181,16 +184,15 @@ fn document_units(s: &mut Session, p: &Value) -> Result<Value> {
             .map(|p| (p.name.clone(), p.expr.trim().to_string()))
             .collect();
         for (name, e) in bare {
+            let now = same(&s.doc.length_inputs());
             let probe = {
                 let mut d = (*s.doc).clone();
-                let _ = d.change_param(&name, &format!("{e} {old}"), None, None);
-                d.param_values().0
+                let _ = d.change_param(&name, &format!("{e} {old}"), Some(&old), None);
+                same(&d.length_inputs())
             };
-            // Only when writing the old unit puts the values back where they were.
-            let fixes = before.iter().filter(|(k, b)| probe.get(*k).is_some_and(|a| (a.v - b.v).abs() <= 1e-9 * b.v.abs().max(1.0))).count()
-                > before.iter().filter(|(k, b)| after.get(*k).is_some_and(|a| (a.v - b.v).abs() <= 1e-9 * b.v.abs().max(1.0))).count();
-            if fixes {
-                s.doc_mut().change_param(&name, &format!("{e} {old}"), None, None)?;
+            // Only when writing the old unit puts more inputs back where they were.
+            if probe > now {
+                s.doc_mut().change_param(&name, &format!("{e} {old}"), Some(&old), None)?;
                 kept.push(name);
             }
         }

crates/engine/src/tests.rs

@@ -1467,3 +1467,15 @@ fn booleans_stay_in_their_component() {
     assert!((vol(&mut s, "BBox") - (2000.0 - 8.0 * 6.0 * 10.0)).abs() < 1e-6, "{}", vol(&mut s, "BBox"));
     assert!(s.execute("Extrude", &json!({"sketch": "Slot", "distance": 1, "operation": "cut", "participants": ["Nope"]})).is_err());
 }
+
+/// A unit-less parameter used as a length means the design's units.
+#[test]
+fn unitless_parameters_used_as_lengths_take_the_design_units() {
+    let mut s = Session::default();
+    s.doc_mut().units = "in".into();
+    run(&mut s, "parameters.add", json!({"name": "w", "expression": "2", "unit": ""}));
+    run(&mut s, "PrimitiveBox", json!({"length": "w", "width": "w * 1", "height": "10 mm"}));
+    let m = run(&mut s, "MeasureCommand", json!({}));
+    let max = |i: usize| m["bodies"][0]["bbox"]["max"][i].as_f64().unwrap_or(0.0);
+    assert!((max(0) - 50.8).abs() < 1e-9 && (max(1) - 50.8).abs() < 1e-9 && (max(2) - 10.0).abs() < 1e-9, "{m}");
+}