fix(editor): Hardened fixed point and bound element parsing in restore (#10816)

* fix: Reinforce fixedPoint restore

Signed-off-by: Mark Tolmacs <mark@lazycat.hu>

* fix: Even more hardened boundElement in restore

Signed-off-by: Mark Tolmacs <mark@lazycat.hu>

* fix: Extract constant

Signed-off-by: Mark Tolmacs <mark@lazycat.hu>

* fix: Remove superfluous check from restore

Signed-off-by: Mark Tolmacs <mark@lazycat.hu>

* chore: Remove non-needed code path

Signed-off-by: Mark Tolmacs <mark@lazycat.hu>

* fix: More robust number test for fixedPoint parsing

Signed-off-by: Mark Tolmacs <mark@lazycat.hu>

* fix: Validate bindings for element being parsed

Signed-off-by: Mark Tolmacs <mark@lazycat.hu>

* unrelated type safety

---------

Signed-off-by: Mark Tolmacs <mark@lazycat.hu>
Co-authored-by: dwelle <5153846+dwelle@users.noreply.github.com>

packages/element/src/binding.ts

@@ -2447,21 +2447,37 @@ export const getArrowLocalFixedPoints = (
   ];
 };
 
-export const normalizeFixedPoint = <T extends FixedPoint | null>(
+export const isFixedPoint = (
+  fixedPoint: any,
+): fixedPoint is FixedPointBinding["fixedPoint"] => {
+  return (
+    Array.isArray(fixedPoint) &&
+    fixedPoint.length === 2 &&
+    fixedPoint.every((coord) => Number.isFinite(coord))
+  );
+};
+
+export const normalizeFixedPoint = <T extends FixedPoint>(
   fixedPoint: T,
-): T extends null ? null : FixedPoint => {
+): FixedPoint => {
+  if (!isFixedPoint(fixedPoint)) {
+    return [0.5001, 0.5001];
+  }
+
+  const EPSILON = 0.0001;
+
   // Do not allow a precise 0.5 for fixed point ratio
   // to avoid jumping arrow heading due to floating point imprecision
   if (
-    fixedPoint &&
+    Math.abs(fixedPoint[0] - 0.5) < EPSILON ||
-    (Math.abs(fixedPoint[0] - 0.5) < 0.0001 ||
+    Math.abs(fixedPoint[1] - 0.5) < EPSILON
-      Math.abs(fixedPoint[1] - 0.5) < 0.0001)
   ) {
     return fixedPoint.map((ratio) =>
-      Math.abs(ratio - 0.5) < 0.0001 ? 0.5001 : ratio,
+      Math.abs(ratio - 0.5) < EPSILON ? 0.5001 : ratio,
-    ) as T extends null ? null : FixedPoint;
+    ) as FixedPoint;
   }
-  return fixedPoint as any as T extends null ? null : FixedPoint;
+
+  return fixedPoint;
 };
 
 type Side =

packages/excalidraw/data/restore.ts

@@ -155,7 +155,7 @@ const repairBinding = <T extends ExcalidrawArrowElement>(
         | ExcalidrawElbowArrowElement["startBinding"]
         | ExcalidrawElbowArrowElement["endBinding"] = {
         ...binding,
-        fixedPoint: normalizeFixedPoint(binding.fixedPoint ?? [0, 0]),
+        fixedPoint: normalizeFixedPoint(binding.fixedPoint),
         mode: binding.mode || "orbit",
       };
 
@@ -176,7 +176,7 @@ const repairBinding = <T extends ExcalidrawArrowElement>(
         return {
           elementId: binding.elementId,
           mode: binding.mode,
-          fixedPoint: normalizeFixedPoint(binding.fixedPoint || [0.5, 0.5]),
+          fixedPoint: normalizeFixedPoint(binding.fixedPoint),
         } as FixedPointBinding | null;
       }
       return null;
@@ -185,15 +185,14 @@ const repairBinding = <T extends ExcalidrawArrowElement>(
     // binding schema v1 (legacy) -> attempt to migrate to v2
     // ---------------------------------------------------------------------------
 
-    const targetBoundElement =
+    const targetBoundElement = targetElementsMap.get(binding.elementId) as
-      (targetElementsMap.get(binding.elementId) as ExcalidrawBindableElement) ||
+      | ExcalidrawBindableElement
-      undefined;
+      | undefined;
     const boundElement =
       targetBoundElement ||
-      (existingElementsMap?.get(
+      (existingElementsMap?.get(binding.elementId) as
-        binding.elementId,
+        | ExcalidrawBindableElement
-      ) as ExcalidrawBindableElement) ||
+        | undefined);
-      undefined;
     const elementsMap = targetBoundElement
       ? targetElementsMap
       : existingElementsMap;
@@ -208,11 +207,28 @@ const repairBinding = <T extends ExcalidrawArrowElement>(
       const mode = isPointInElement(p, boundElement, elementsMap)
         ? "inside"
         : "orbit";
+      const safeElement = {
+        ...element,
+        startBinding: element.startBinding?.elementId
+          ? {
+              ...element.startBinding,
+              mode,
+              fixedPoint: normalizeFixedPoint(element.startBinding.fixedPoint),
+            }
+          : null,
+        endBinding: element.endBinding?.elementId
+          ? {
+              ...element.endBinding,
+              mode,
+              fixedPoint: normalizeFixedPoint(element.endBinding.fixedPoint),
+            }
+          : null,
+      };
       const focusPoint =
         mode === "inside"
           ? p
           : projectFixedPointOntoDiagonal(
-              element,
+              safeElement,
               p,
               boundElement,
               startOrEnd,
@@ -220,7 +236,7 @@ const repairBinding = <T extends ExcalidrawArrowElement>(
               { value: 1 as NormalizedZoomValue },
             ) || p;
       const { fixedPoint } = calculateFixedPointForNonElbowArrowBinding(
-        element,
+        safeElement,
         boundElement,
         startOrEnd,
         elementsMap,