Fix #3357. Remove Shift-E for parametric objects (superseded by tab) and you can now extend to anything not just slabs.

This Shift-E still needs more polish as we figure out the best hotkeys
and what's most natural to users when they select different combinations
of objects, so expect the conditionals that govern when Shift-E does
things to still change in the future.

src/bonsai/bonsai/bim/module/model/wall.py

@@ -36,7 +36,7 @@ import bonsai.core.geometry
 import bonsai.core.model as core
 import bonsai.tool as tool
 from bonsai.bim.ifc import IfcStore
-from math import pi, sin, cos, degrees, radians
+from math import pi, sin, cos, degrees
 from mathutils import Vector, Matrix
 from bonsai.bim.module.model.opening import FilledOpeningGenerator
 from bonsai.bim.module.model.decorator import PolylineDecorator, ProductDecorator
@@ -58,6 +58,26 @@ class UnjoinWalls(bpy.types.Operator, tool.Ifc.Operator):
         core.unjoin_walls(tool.Ifc, tool.Blender, tool.Geometry, DumbWallJoiner(), tool.Model)
 
 
+class ExtendWallsToUnderside(bpy.types.Operator, tool.Ifc.Operator):
+    bl_idname = "bim.extend_walls_to_underside"
+    bl_label = "Extend Walls To Underside"
+    bl_description = "Extend and clip selected walls at the bottom faces of an object"
+    bl_options = {"REGISTER", "UNDO"}
+
+    def _execute(self, context):
+        slab = None
+        walls = []
+        if (obj := tool.Blender.get_active_object(is_selected=True)) and (element := tool.Ifc.get_entity(obj)):
+            slab = obj
+        for obj in tool.Blender.get_selected_objects(include_active=False):
+            if (element := tool.Ifc.get_entity(obj)) and tool.Model.get_usage_type(element) == "LAYER2":
+                walls.append(obj)
+        if slab and walls:
+            core.extend_wall_to_slab(tool.Ifc, tool.Geometry, tool.Model, slab, walls)
+        else:
+            self.report({"ERROR"}, "Please select at least one LAYER2 element and an active element")
+
+
 class AlignWall(bpy.types.Operator):
     bl_idname = "bim.align_wall"
     bl_label = "Align Wall"