`getFirstFinalizedProtoInstance()` returns `NULL` for DEF with Lua code in v2023b

[galou]

Describe the Bug It seems that something is wrong with DEF with Lua code. We have a node defined like this

DEF %{= "LED_" .. name_suffix }% LED {
...
}

For this node, node->getFirstFinalizedProtoInstance(); returns NULL.

This happens with v2023b but was working with v2023a.

Steps to Reproduce

1. Use Lua code in DEF
2. In your Python controller, call getPosition()
3. See the log

WARNING: Pose  > DEF LASER_EMITTER LaserEmitter: Cannot get the PROTO instance for node 'LED_XMINUS_1' of type 'LED'.
WARNING: Pose  > DEF LASER_EMITTER LaserEmitter: wb_supervisor_node_get_position() can exclusively be used with Pose (or derived).

4. getPosition() returns [nan, nan, nan].

Expected behavior It should work as in used to do in v2023a.

System

• Operating System: Linux Ubuntu 22.04
• Graphics Card: irrelevant

I'm ready to solve the issue but need some hint where to start.

[omichel]

Unfortunately, I have no idea on how to fix this. I would recommend the following to investigate:

1. Check if the problem is the same with a Javascript proto (instead of Lua).
2. Check the change log of R2023b to identify which PR may have caused this bug.

[galou]

Candidates: #5978, #5676, #5774.

[galou]

A PROTO with Javascript rather than Lua suffers from the same symptoms.

[galou]

Can I debug the generated PROTO files (after going through the engine)?

[omichel]

Yes, there is a menu in the scene tree allowing to see the generated proto file.

[galou]

When trying to write a small example to reproduce the issue, I wrote this PROTO:

#VRML_SIM R2023b utf8
#     Robot {
#       children [
#         DEF led LED {
#         }
#       ]
#       controller "my_supervisor"
#       supervisor TRUE
#     }
# 


PROTO MyRobot [
  field SFVec3f translation 0 0 0
  field SFRotation rotation 0 0 1 0
  field SFString name "robot"
]
{
  Robot {
    translation IS translation
    rotation IS rotation
    name IS name
    controller "my_supervisor"
    supervisor TRUE
    children [
        DEF %{= "led" }% LED {
        }
    ]
  }
}

with this supervisor:

"""my_supervisor controller."""

# You may need to import some classes of the controller module. Ex:
#  from controller import Robot, Motor, DistanceSensor
from controller import Supervisor

class Test(Supervisor):

    def __init__(self):
        super().__init__()

    def run(self):
        my_led = self.getFromDef('my_led')
        led = my_led.getFromProtoDef('led')
        print(f'{led=}')
        print(f'{led.getPosition()=}')

controller = Test()
controller.run()

and this world

#VRML_SIM R2023b utf8

EXTERNPROTO "https://raw.githubusercontent.com/cyberbotics/webots/26e08bbf6049f8d3ec3af3dd874e5f5d4062ab96/projects/objects/backgrounds/protos/TexturedBackground.proto"
EXTERNPROTO "https://raw.githubusercontent.com/cyberbotics/webots/26e08bbf6049f8d3ec3af3dd874e5f5d4062ab96/projects/objects/backgrounds/protos/TexturedBackgroundLight.proto"
EXTERNPROTO "../protos/MyRobot.proto"

WorldInfo {
}
Viewpoint {
  orientation -0.5773502691896257 0.5773502691896257 0.5773502691896257 2.0944
  position 0 0 10
}
TexturedBackground {
}
TexturedBackgroundLight {
}
DEF transform Pose {
  children [
    DEF my_led MyRobot {
    }
  ]
}

but this combination does NOT trigger the issue. I'll have to dig farther.

[galou]

I'm trying to understand the code. What is a PROTO parameter node? In our case, when the issue appears, protoParameterNodeInstances() returns an empty list.

[omichel]

I am not sure, but it could be the nodes that are passed as PROTO parameters.

[galou]

Do you mean a parameter whose type is a node?

[omichel]

Yes.

[galou]

git bisect allowed to determine that the bug was introduced in b95a7360fddc9fa5024f1c51facfce35a5d3e7c7 "Refactor node and PROTO creation (#5779)"

[omichel]

Nice catch! I would suggest you to investigate commit-per-commit on #5779 to understand which commit did introduce the bug. Unfortunately @stefaniapedrazzi is not working any more with us and won't be able to help you on this.