From 91d36e9b81a5087b0000b8abc1bcdb3fadeb807f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?M=C3=A1rk=20Tolm=C3=A1cs?= <mark@lazycat.hu>
Date: Thu, 22 May 2025 12:34:15 +0200
Subject: [PATCH] fix: Linear to elbow conversion crash (#9556)

* Fix linear to elbow conversion

* Add invariant check

* Add dev invariant fix

* Add arrowhead
---
 packages/element/src/elbowArrow.ts            | 19 +++++++++++++++++++
 .../components/ConvertElementTypePopup.tsx    |  3 ++-
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/packages/element/src/elbowArrow.ts b/packages/element/src/elbowArrow.ts
index 95a2aa8ef..73c82a898 100644
--- a/packages/element/src/elbowArrow.ts
+++ b/packages/element/src/elbowArrow.ts
@@ -974,6 +974,25 @@ export const updateElbowArrowPoints = (
         ),
       "Elbow arrow segments must be either horizontal or vertical",
     );
+
+    invariant(
+      updates.fixedSegments?.find(
+        (segment) =>
+          segment.index === 1 &&
+          pointsEqual(segment.start, (updates.points ?? arrow.points)[0]),
+      ) == null &&
+        updates.fixedSegments?.find(
+          (segment) =>
+            segment.index === (updates.points ?? arrow.points).length - 1 &&
+            pointsEqual(
+              segment.end,
+              (updates.points ?? arrow.points)[
+                (updates.points ?? arrow.points).length - 1
+              ],
+            ),
+        ) == null,
+      "The first and last segments cannot be fixed",
+    );
   }
 
   const fixedSegments = updates.fixedSegments ?? arrow.fixedSegments ?? [];
diff --git a/packages/excalidraw/components/ConvertElementTypePopup.tsx b/packages/excalidraw/components/ConvertElementTypePopup.tsx
index b1dd11cb4..8e527d549 100644
--- a/packages/excalidraw/components/ConvertElementTypePopup.tsx
+++ b/packages/excalidraw/components/ConvertElementTypePopup.tsx
@@ -564,7 +564,7 @@ export const convertElementTypes = (
               continue;
             }
             const fixedSegments: FixedSegment[] = [];
-            for (let i = 0; i < nextPoints.length - 1; i++) {
+            for (let i = 1; i < nextPoints.length - 2; i++) {
               fixedSegments.push({
                 start: nextPoints[i],
                 end: nextPoints[i + 1],
@@ -581,6 +581,7 @@ export const convertElementTypes = (
             );
             mutateElement(element, app.scene.getNonDeletedElementsMap(), {
               ...updates,
+              endArrowhead: "arrow",
             });
           } else {
             // if we're converting to non-elbow linear element, check if