From 41101efaa5fdcc83be7422d31378e7fabe9cbf0d Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Sat, 19 Sep 2026 15:45:18 +0000
Subject: [PATCH] fix(trim): skip empty preview polyline segment samples

Co-authored-by: dasmatus <330471626+dasmatus@users.noreply.github.com>
(cherry picked from commit fb13a7aaa6b1505d749c384cbdbbaa80bc040c4b)
---
 src/modules/draw/modify/trim.rs | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/src/modules/draw/modify/trim.rs b/src/modules/draw/modify/trim.rs
index 31f29e3cd..f6347ca6e 100644
--- a/src/modules/draw/modify/trim.rs
+++ b/src/modules/draw/modify/trim.rs
@@ -3859,6 +3859,23 @@ mod tests {
             "the shared vertex appears once, not twice: {pts:?}"
         );
     }
+
+    #[test]
+    fn preview_sampling_skips_edge_on_polyline2d_arc_segments() {
+        use acadrust::entities::{Polyline2D, Vertex2D};
+
+        let mut pl = Polyline2D::new();
+        let mut start = Vertex2D::new(Vector3::new(0.0, 0.0, 0.0));
+        start.bulge = 1.0;
+        pl.vertices = vec![start, Vertex2D::new(Vector3::new(2.0, 0.0, 0.0))];
+        pl.normal = Vector3::new(1.0, 0.0, 0.0);
+
+        let pts = preview_sample_xy(&EntityType::Polyline2D(pl));
+        assert!(
+            pts.is_empty(),
+            "edge-on arc segments are skipped instead of panicking: {pts:?}"
+        );
+    }
 }
 
 // ══════════════════════════════════════════════════════════════════════════
@@ -4086,6 +4103,9 @@ fn preview_sample_xy(e: &EntityType) -> Vec<[f64; 2]> {
                     }
                     _ => sample_entity_xy(&seg),
                 };
+                if sp.is_empty() {
+                    continue;
+                }
                 if pts.last() == sp.first() {
                     pts.extend_from_slice(&sp[1..]);
                 } else {