[Core feature] Support warnings in task outputs

[EngHabu]

Motivation: Why do you think this is important?

Sometimes "problems" happen during a task execution that don't warrant a failure but are good to be reported to the user so they can address them.
An example of this is if you forget to install flytekitplugins-dec-standard, the task will fail to write out Decks and because that's not a core functionality, it fails silently with just a log line while letting the task succeed.

Goal: What should the final outcome look like, ideally?

A task can produce warnings as part of its output (either generated by the system or the user) and these should be collected, visualized in the UI and bubbled up to the user.

Describe alternatives you've considered

Return an additional explicit output.

Propose: Link/Inline OR Additional context

No response

Are you sure this issue hasn't been raised already?

• Yes

Have you read the Code of Conduct?

• Yes

[runllm]

To implement warnings in task outputs in Flyte, consider using a custom output type that includes a warnings field. This approach allows tasks to return both their primary outputs and any warnings. Modify the task's signature to include a warnings list and ensure these are displayed in the Flyte console. Here’s an example using Python:

from typing import List, Tuple
from flytekit import task, workflow

@task
def example_task() -> Tuple[str, List[str]]:
    warnings = []
    # Example condition that triggers a warning
    if True:
        warnings.append("This is a warning message.")
    return "Task completed successfully.", warnings

@workflow
def example_workflow() -> Tuple[str, List[str]]:
    result, warnings = example_task()
    return result, warnings

This code defines a task that returns a tuple of a result and a list of warnings. The workflow captures and returns both. Adjust the UI to display these warnings appropriately.

Would you like more details on integrating this with the Flyte UI or any other aspect?

Sources:

• https://discuss.flyte.org/t/9499661/hello-does-anyone-know-why-i-am-seeing-the-cache-was-disable/
• https://discuss.flyte.org/t/16645914/is-there-a-way-to-propogate-some-important-output-to-a-flyte/

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[eapolinario]

This is related to an old discussion: #3838.

We also talked about this and the naive solution to add another file (e.g. warnings.pb) to describe these special warnings can lead to a performance hit, so it's undesirable.