Improved user error messaging around obj import errors

Tightly capturing all 600 (git status) errors reported that were directly due to errors in the built in OBJ importer. Some of these are likely due to corrupted obj files, and thus suggesting it is done again.

MCprep_addon/world_tools.py

@@ -269,11 +269,71 @@ def execute(self, context):
 			self.report({"ERROR"}, "Select the .obj file, NOT the .mtl!")
 			return {'CANCELLED'}
 
-		if not "obj" in dir(bpy.ops.import_scene):
+		if "obj" not in dir(bpy.ops.import_scene):
 			self.report({"INFO"}, "FYI: had to enable OBJ imports in user preferences")
 			bpy.ops.preferences.addon_enable(module="io_scene_obj")
 
-		res = bpy.ops.import_scene.obj(filepath=self.filepath, use_split_groups=True)
+		# There are a number of bug reports that come from the generic call
+		# of obj importing. If this fails, should notify the user to try again
+		# or try exporting again.
+		#
+		# In order to not overly supress error messages, below we only capture
+		# very tight specific errors possible, so that other errors still get
+		# reported so it may be passed off to blender devs. It is understood the
+		# below errors are not internationalized, so someone with another lang
+		# set will get the raw bubbled up traceback.
+		obj_import_err_msg = (
+			"Blender's OBJ importer error, try re-exporting your world and "
+			"import again.")
+		obj_import_mem_msg = (
+			"Memory error during OBJ import, try exporting a smaller world")
+		try:
+			res = bpy.ops.import_scene.obj(
+				filepath=self.filepath, use_split_groups=True)
+		except MemoryError as err:
+			print("Memory error during import OBJ:")
+			print(err)
+			self.report({"ERROR"}, obj_import_mem_msg)
+			return {'CANCELLED'}
+		except ValueError as err:
+			if "could not convert string" in str(err):
+				# Error such as:
+				#   vec[:] = [float_func(v) for v in line_split[1:]]
+				#   ValueError: could not convert string to float: b'6848/28'
+				self.report({"ERROR"}, obj_import_err_msg)
+				return {'CANCELLED'}
+			elif "invalid literal for int() with base" in str(err):
+				# Error such as:
+				#   idx = int(obj_vert[0])
+				#   ValueError: invalid literal for int() with base 10: b'4semtl'
+				self.report({"ERROR"}, obj_import_err_msg)
+				return {'CANCELLED'}
+			else:
+				raise err
+		except IndexError as err:
+			if "list index out of range" in str(err):
+				self.report({"ERROR"}, obj_import_err_msg)
+				return {'CANCELLED'}
+			else:
+				raise err
+		except UnicodeDecodeError as err:
+			if "codec can't decode byte" in str(err):
+				# Error such as:
+				#   keywords["relpath"] = os.path.dirname(bpy.data.filepath)
+				#   UnicodeDecodeError: 'utf-8' codec can't decode byte 0xc4 in
+				#     position 24: invalid continuation byte
+				self.report({"ERROR"}, obj_import_err_msg)
+				return {'CANCELLED'}
+			else:
+				raise err
+		except AttributeError as err:
+			if "object has no attribute 'image'" in str(err):
+				# Error such as:
+				#   nodetex.image = image
+				#   AttributeError: 'NoneType' object has no attribute 'image'
+				self.report({"ERROR"}, obj_import_err_msg)
+				return {'CANCELLED'}
+
 		if res != {'FINISHED'}:
 			self.report({"ERROR"}, "Issue encountered while importing world")
 			return {'CANCELLED'}