fix gantt flickering #42215

[darkag]

---

closes: #42215

Fix gantt flickering issue. if someone can label it to legacy ui

[jscheffl]

Before merge - for local testing - can you tell me a good example DAG/run such that I can test it locally? I am sure I have seen it myself flickering but I'd like to ensure I am looking at the right place... as I did not note down where...

[darkag]

Sure, here is step to reproduce the issue with the the following dag

from __future__ import annotations

import pendulum

from airflow.decorators import dag, task
from airflow.operators.empty import EmptyOperator


# [START dag_decorator_usage]
@dag(
    schedule=None,
    start_date=pendulum.datetime(2021, 1, 1, tz="UTC"),
    catchup=False,
    tags=["example"],
    dag_display_name="Sample DAG with Display Name",
)
def example_display_name():
    sample_task_1 = EmptyOperator(
        task_id="sample_task_1",
        task_display_name="Sample Task 1",
    )

    @task(task_display_name="Sample Task 2")
    def sample_task_2():
        pass

    sample_task_1 >> sample_task_2()


example_dag = example_display_name()

trigger a dag run of this dag
clear "Sample task 2"

with the fix, the gantt gaph should look to something like this

without it will result as something like this:

[jscheffl]

That really seems to work. Thanks for the fix!

[github-actions]

Backport successfully created: v2-10-test

Status	Branch	Result
✅	v2-10-test