Emboss: say how far the picked point is from a face (#392) (#1733)

Thanks @SychPL.

crates/engine/src/cmd/features_more.rs

@@ -161,6 +161,8 @@ fn emboss(s: &mut Session, p: &Value) -> Result<Value> {
         let at = solidcraft_doc::apply_point(&s.active_component_frame(), local);
         let state = s.world_state();
         let mut candidates = Vec::new();
+        // The nearest face off the point: (distance, body), for the error when none holds it.
+        let mut nearest: Option<(f64, &str)> = None;
         for body in &state.bodies {
             let definition = body.definition_name();
             if !targets.is_empty() && !targets.iter().any(|n| n == definition || n == &body.name) {
@@ -179,14 +181,30 @@ fn emboss(s: &mut Session, p: &Value) -> Result<Value> {
                     inside.then_some(((at - a).dot(n).abs(), *face as usize))
                 })
                 .min_by(|a, b| a.0.total_cmp(&b.0));
-            if let Some((distance, index)) = closest
-                && distance < (body.body.size() * 1e-3).max(1e-3)
-            {
-                candidates.push((body, index));
+            match closest {
+                Some((distance, index)) if distance < (body.body.size() * 1e-3).max(1e-3) => candidates.push((body, index)),
+                Some((distance, _)) if nearest.is_none_or(|(d, _)| distance < d) => nearest = Some((distance, body.name.as_str())),
+                _ => {}
             }
         }
-        if candidates.len() != 1 {
-            return Err(bad(cmd, "`face` must identify exactly one target body surface"));
+        // #392: say what is wrong with the point, not only that it picks no single face.
+        let point = format!("[{}, {}, {}]", local.x, local.y, local.z);
+        match (candidates.as_slice(), nearest) {
+            ([], Some((d, body))) => {
+                return Err(bad(
+                    cmd,
+                    format!("`face` {point} lies on no face: the nearest, on `{body}`, is {d:.3} mm away; give a point on the face"),
+                ));
+            }
+            ([], None) => return Err(bad(cmd, format!("`face` {point} lies on no face of the target bodies"))),
+            ([_], _) => {}
+            (more, _) => {
+                let names: Vec<&str> = more.iter().map(|(b, _)| b.name.as_str()).collect();
+                return Err(bad(
+                    cmd,
+                    format!("`face` {point} lies on faces of {} bodies ({}): name one in `targets`", names.len(), names.join(", ")),
+                ));
+            }
         }
         let (selected, index) = candidates.first().copied().ok_or_else(|| bad(cmd, "no target face"))?;
         let name = selected.definition_name();

crates/engine/src/cmd/features_more_tests.rs

@@ -92,6 +92,23 @@ fn emboss_and_deboss_on_a_face() {
     assert!(s.execute("solid.emboss", &json!({"sketch": "Logo", "depth": 1, "mode": "sideways"})).is_err());
 }
 
+#[test]
+fn emboss_face_off_the_part_says_how_far() {
+    // #392: a point beside the face was refused with "`face` must identify exactly one target
+    // body surface", which didn't say the point was off the face.
+    let mut s = Session::default();
+    run(&mut s, "solid.box", json!({"length": 40, "width": 30, "height": 10, "body_name": "A"}));
+    run(&mut s, "sketch.create", json!({"plane": {"face": [20, 15, 10]}, "name": "Logo"}));
+    run(&mut s, "sketch.rectangle.two_point", json!({"p0": [5, 5], "p1": [15, 15]}));
+    run(&mut s, "sketch.finish", json!({}));
+    let e = s.execute("solid.emboss", &json!({"sketch": "Logo", "depth": 1, "face": [20, 15, 11.25]})).unwrap_err().to_string();
+    assert!(e.contains("[20, 15, 11.25] lies on no face: the nearest, on `A`, is 1.250 mm away"), "{e}");
+    run(&mut s, "solid.box", json!({"length": 10, "width": 30, "height": 10, "corner": [40, 0, 0], "operation": "new_body", "body_name": "B"}));
+    let e = s.execute("solid.emboss", &json!({"sketch": "Logo", "depth": 1, "face": [40, 15, 5]})).unwrap_err().to_string();
+    assert!(e.contains("lies on faces of 2 bodies (A, B): name one in `targets`"), "{e}");
+    run(&mut s, "solid.emboss", json!({"sketch": "Logo", "depth": 1, "face": [20, 15, 10]}));
+}
+
 fn cylinder_badge() -> Session {
     let mut s = Session::default();
     run(&mut s, "parameters.add", json!({"name":"badge_depth","expression":"1 mm"}));