From 1ac2ebaad2e5072fbff3f8606a3cd9286b8cd849 Mon Sep 17 00:00:00 2001
From: NetterSilver <133535268+Silvertree2010@users.noreply.github.com>
Date: Mon, 19 Oct 2026 08:31:44 +0200
Subject: [PATCH] Keep line and arc elevation when lengthening with LENGTHEN
 (#1313)

Found while testing crates/engine/src/cmd/modify2.rs:764

Co-authored-by: Claude Haiku 5.5 <noreply@anthropic.com>
---
 crates/engine/src/cmd/modify2.rs       | 11 +++++++--
 crates/engine/src/cmd/modify2_tests.rs | 33 ++++++++++++++++++++++++++
 2 files changed, 42 insertions(+), 2 deletions(-)

diff --git a/crates/engine/src/cmd/modify2.rs b/crates/engine/src/cmd/modify2.rs
index 5562f969c..37a48092b 100644
--- a/crates/engine/src/cmd/modify2.rs
+++ b/crates/engine/src/cmd/modify2.rs
@@ -761,7 +761,13 @@ pub(crate) fn lengthen_kind(k: &EntityKind, pick: Option<Vec2>, mode: LenMode) -
                 return Err(too_short());
             }
             let ne = fixed + dir * nl;
-            Ok(if at_b { line(a, ne) } else { line(ne, b) })
+            let mut out = l.clone();
+            if at_b {
+                out.b = ne.to3(l.b.z);
+            } else {
+                out.a = ne.to3(l.a.z);
+            }
+            Ok(EntityKind::Line(out))
         }
         EntityKind::Arc(ar) => {
             let g = Arc::new(ar.center.xy(), ar.radius, ar.start, ar.end);
@@ -782,7 +788,8 @@ pub(crate) fn lengthen_kind(k: &EntityKind, pick: Option<Vec2>, mode: LenMode) -
             if !(ns > 1e-12 && ns < TAU - 1e-9) {
                 return Err(other("The new arc would be zero length or a full circle."));
             }
-            Ok(if at_end { arc(&Arc::new(g.center, g.radius, g.start, g.start + ns)) } else { arc(&Arc::new(g.center, g.radius, g.end - ns, g.end)) })
+            let na = if at_end { Arc::new(g.center, g.radius, g.start, g.start + ns) } else { Arc::new(g.center, g.radius, g.end - ns, g.end) };
+            Ok(EntityKind::Arc(cadcraft_doc::Arc { radius: na.radius, start: na.start, end: na.end, ..ar.clone() }))
         }
         EntityKind::LwPolyline(p) if !p.closed && p.vertices.len() >= 2 => {
             let total = Polyline { vertices: p.vertices.clone(), closed: false }.len();
diff --git a/crates/engine/src/cmd/modify2_tests.rs b/crates/engine/src/cmd/modify2_tests.rs
index 9b76c84fc..836e5c017 100644
--- a/crates/engine/src/cmd/modify2_tests.rs
+++ b/crates/engine/src/cmd/modify2_tests.rs
@@ -214,6 +214,39 @@ fn lengthen_json() {
     assert!(near(poly(&kind(&s, &p)).vertices[0].p, -5.0, 10.0));
 }
 
+#[test]
+fn lengthen_keeps_elevation() {
+    let mut s = Session::new();
+    let l = h(&s.execute("line", &json!({"points": [[0, 0], [10, 0]]})).unwrap());
+    let a = h(&s.execute("arc", &json!({"center": [0, 0], "radius": 1, "start": 0, "end": 90})).unwrap());
+    let doc = s.doc_mut().unwrap();
+    doc.modify_entity(Handle::parse_hex(&l).unwrap(), |e| {
+        if let EntityKind::Line(x) = &mut e.kind {
+            x.a.z = 5.0;
+            x.b.z = 5.0;
+        }
+    })
+    .unwrap();
+    doc.modify_entity(Handle::parse_hex(&a).unwrap(), |e| {
+        if let EntityKind::Arc(x) = &mut e.kind {
+            x.center.z = 3.0;
+        }
+    })
+    .unwrap();
+    s.execute("lengthen", &json!({"handle": l, "delta": 2})).unwrap();
+    let EntityKind::Line(x) = kind(&s, &l) else { panic!("not a line") };
+    assert_eq!((x.a.x, x.a.y, x.a.z), (0.0, 0.0, 5.0));
+    assert_eq!((x.b.x, x.b.y, x.b.z), (12.0, 0.0, 5.0));
+    s.execute("lengthen", &json!({"handle": l, "delta": 1, "pick": [0, 0]})).unwrap();
+    let EntityKind::Line(x) = kind(&s, &l) else { panic!("not a line") };
+    assert_eq!((x.a.x, x.a.y, x.a.z), (-1.0, 0.0, 5.0));
+    assert_eq!((x.b.x, x.b.y, x.b.z), (12.0, 0.0, 5.0));
+    s.execute("lengthen", &json!({"handle": a, "deltaAngle": 10})).unwrap();
+    let EntityKind::Arc(x) = kind(&s, &a) else { panic!("not an arc") };
+    assert_eq!(x.center.z, 3.0);
+    assert!((arc_of(&kind(&s, &a)).sweep() - 100f64.to_radians()).abs() < 1e-9);
+}
+
 #[test]
 fn lengthen_command_line() {
     let mut s = Session::new();