See #4946. Slowly start refactoring out model module into core for better error handling.

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

@@ -32,6 +32,7 @@ import blenderbim.bim.handler
 import blenderbim.core.type
 import blenderbim.core.root
 import blenderbim.core.geometry
+import blenderbim.core.model as core
 import blenderbim.tool as tool
 from blenderbim.bim.ifc import IfcStore
 from math import pi, sin, cos, degrees
@@ -80,14 +81,12 @@ class JoinWall(bpy.types.Operator, tool.Ifc.Operator):
             return {"FINISHED"}
 
         if self.join_type in ("L", "V"):
-            if len(selected_objs) != 2:
-                self.report({"ERROR"}, f"It requires 2 selected objects to do join of type {self.join_type}")
+            try:
+                core.join_wall_LV(tool.Blender, joiner, join_type=self.join_type)
+            except core.RequireTwoObjectsError:
+                join_type_name = {"L": "butt", "V": "mitre"}[self.join_type]
+                self.report({"ERROR"}, f"Please select 2 objects to do a {join_type_name} joint")
                 return {"CANCELLED"}
-            another_selected_object = next(o for o in selected_objs if o != context.active_object)
-            if self.join_type == "L":
-                joiner.join_L(another_selected_object, context.active_object)
-            elif self.join_type == "V":
-                joiner.join_V(another_selected_object, context.active_object)
             return {"FINISHED"}
 
         if self.join_type == "T":

src/blenderbim/blenderbim/bim/module/model/workspace.py

@@ -21,11 +21,11 @@ import bpy
 import ifcopenshell
 import ifcopenshell.util.unit
 import blenderbim.tool as tool
-import blenderbim.bim.module.type.prop as type_prop
+import blenderbim.core.model
+from blenderbim.bim.module.model.wall import DumbWallJoiner
 from blenderbim.bim.helper import prop_with_search
 from bpy.types import WorkSpaceTool
 from blenderbim.bim.module.model.data import AuthoringData
-from blenderbim.bim.module.drawing.data import DecoratorData
 from blenderbim.bim.module.system.data import PortData
 from blenderbim.bim.module.model.prop import get_ifc_class
 
@@ -781,7 +781,11 @@ class Hotkey(bpy.types.Operator, tool.Ifc.Operator):
         if not bpy.context.selected_objects:
             return
         if self.active_material_usage == "LAYER2":
-            bpy.ops.bim.join_wall(join_type="L")
+            try:
+                blenderbim.core.model.join_wall_LV(tool.Blender, DumbWallJoiner(), join_type="L")
+            except blenderbim.core.model.RequireTwoObjectsError:
+                self.report({"ERROR"}, "Please select 2 objects to do a butt joint")
+                return {"CANCELLED"}
         elif self.active_material_usage == "PROFILE":
             bpy.ops.bim.extend_profile(join_type="L")
 
@@ -806,7 +810,11 @@ class Hotkey(bpy.types.Operator, tool.Ifc.Operator):
         if not bpy.context.selected_objects:
             return
         if self.active_material_usage == "LAYER2":
-            bpy.ops.bim.join_wall(join_type="V")
+            try:
+                blenderbim.core.model.join_wall_LV(tool.Blender, DumbWallJoiner(), join_type="V")
+            except blenderbim.core.model.RequireTwoObjectsError:
+                self.report({"ERROR"}, "Please select 2 objects to do a mitre joint")
+                return {"CANCELLED"}
         elif self.active_class in ("IfcDuctSegment", "IfcPipeSegment", "IfcCableCarrierSegment", "IfcCableSegment"):
             bpy.ops.bim.fit_flow_segments()
         elif self.active_material_usage == "PROFILE":

src/blenderbim/blenderbim/core/model.py

@@ -0,0 +1,36 @@
+# BlenderBIM Add-on - OpenBIM Blender Add-on
+# Copyright (C) 2021 Dion Moult <dion@thinkmoult.com>
+#
+# This file is part of BlenderBIM Add-on.
+#
+# BlenderBIM Add-on is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# BlenderBIM Add-on is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with BlenderBIM Add-on.  If not, see <http://www.gnu.org/licenses/>.
+
+import blenderbim.core.tool as tool
+from typing import Literal
+
+
+def join_wall_LV(blender: tool.Blender, joiner, join_type: Literal["L", "V"] = "L") -> None:
+    if len(selected_objs := blender.get_selected_objects()) != 2:
+        raise RequireTwoObjectsError()
+
+    active_obj = blender.get_active_object()
+    another_selected_object = next(o for o in selected_objs if o != active_obj)
+    if join_type == "L":
+        joiner.join_L(another_selected_object, active_obj)
+    elif join_type == "V":
+        joiner.join_V(another_selected_object, active_obj)
+
+
+class RequireTwoObjectsError(Exception):
+    pass