UV: bpy_extras.mesh_utils.mesh_linked_uv_islands raises error in edit mode

Maniphest Tasks: T86484

Differential Revision: https://developer.blender.org/D15778

release/scripts/modules/bpy_extras/mesh_utils.py

@@ -13,14 +13,22 @@ __all__ = (
 
 def mesh_linked_uv_islands(mesh):
     """
-    Splits the mesh into connected polygons, use this for separating cubes from
-    other mesh elements within 1 mesh datablock.
+    Returns lists of polygon indices connected by UV islands.
 
     :arg mesh: the mesh used to group with.
     :type mesh: :class:`bpy.types.Mesh`
-    :return: lists of lists containing polygon indices
+    :return: list of lists containing polygon indices
     :rtype: list
     """
+
+    if mesh.polygons and not mesh.uv_layers.active.data:
+        # Currently, when in edit mode, UV Layer data will always be empty
+        # when accessed though RNA. This may change in the future.
+        raise ValueError(
+            "UV Layers are not currently available from python in Edit Mode. "
+            "Use bmesh and bpy_extras.bmesh_utils.bmesh_linked_uv_islands instead."
+        )
+
     uv_loops = [luv.uv[:] for luv in mesh.uv_layers.active.data]
     poly_loops = [poly.loop_indices for poly in mesh.polygons]
     luv_hash = {}