load and link ifc files by drag'n'drop 🥳

Example - https://imgur.com/a/kIiqk3R

Now you can drag'n'drop files to Blender and they will get loaded as projects (currently there is no safe check whether current project is saved) or you can hold ALT while drag'n'dropping and link single or multiple IFC files.

Actually, it's possible to set it up that way so multiple files won't need ALT modifier (as we can't load multiple projects, only link them) but I've kept ALT modifier for that case too to avoid confusing situations.

Blender 4.1+ only as there wasn't bpy.types.FileHandler before.

src/blenderbim/blenderbim/bim/module/project/__init__.py

@@ -76,6 +76,11 @@ classes = (
     gizmo.ClippingPlane,
 )
 
+if bpy.app.version >= (4, 1, 0):
+    classes += (
+        operator.IFCFileHandlerOperator,
+        operator.BIM_FH_import_ifc,
+    )
 
 addon_keymaps = []
 

src/blenderbim/blenderbim/bim/module/project/operator.py

@@ -2085,3 +2085,46 @@ class BIM_OT_load_clipping_planes(bpy.types.Operator):
             obj.location = values["location"]
             obj.rotation_euler = values["rotation"]
         return {"FINISHED"}
+
+
+if bpy.app.version >= (4, 1, 0):
+
+    class IFCFileHandlerOperator(bpy.types.Operator):
+        bl_idname = "bim.load_project_file_handler"
+        bl_label = "Import .ifc file"
+        bl_options = {"REGISTER", "UNDO", "INTERNAL"}
+
+        directory: bpy.props.StringProperty(subtype="FILE_PATH", options={"SKIP_SAVE", "HIDDEN"})
+        files: bpy.props.CollectionProperty(type=bpy.types.OperatorFileListElement, options={"SKIP_SAVE", "HIDDEN"})
+
+        def invoke(self, context, event):
+            # Keeping code in .invoke() as we'll probably add some
+            # popup windows later.
+
+            # `files` contain only .ifc files.
+            filepath = Path(self.directory)
+            # If user is just drag'n'dropping a single file -> load it as a new project,
+            # if they're holding ALT -> link the file/files to the current project.
+            if event.alt:
+                # Passing self.files directly results in TypeError.
+                serialized_files = [{"name": f.name} for f in self.files]
+                return bpy.ops.bim.link_ifc(directory=self.directory, files=serialized_files)
+            else:
+                if len(self.files) == 1:
+                    return bpy.ops.bim.load_project(filepath=(filepath / self.files[0].name).as_posix())
+                else:
+                    self.report(
+                        {"INFO"},
+                        "To link multiple IFC files hold ALT while drag'n'dropping them.",
+                    )
+                    return {"FINISHED"}
+
+    class BIM_FH_import_ifc(bpy.types.FileHandler):
+        bl_label = "IFC File Handler"
+        bl_import_operator = IFCFileHandlerOperator.bl_idname
+        bl_file_extensions = ".ifc"
+
+        # FileHandler won't work without poll_drop defined.
+        @classmethod
+        def poll_drop(cls, context):
+            return True