Improve Union Transformer Ambiguous Error Message

[Future-Outlier]

Tracking issue

https://flyte-org.slack.com/archives/CP2HDHKE1/p1737474492222339

Why are the changes needed?

Users can debug more effectively if having potential types.

What changes were proposed in this pull request?

1. add potential types variables when doing type transform
2. print potential types if there's an ambiguous case.

How was this patch tested?

unit test and local execution.

from flytekit import task
from dataclasses import dataclass
from typing import Union

@dataclass
class A:
    a: int

@dataclass
class B:
    a: int

@task
def t1() -> Union[A, B]:
    return A(3)

if __name__ == "__main__":
    print(t1())

Setup process

Screenshots

Check all the applicable boxes

• I updated the documentation accordingly.
• All new and existing tests passed.
• All commits are signed-off.

Related PRs

Summary by Bito

Enhanced error messaging system for ambiguous union type transformations, providing more detailed type information. The update includes improved error messages that now display both the ambiguous choice notification and a comprehensive list of potential matching types. These changes aim to improve developer debugging experience.

Unit tests added: True

Estimated effort to review (1-5, lower is better): 1

[flyte-bot]

Code Review Agent Run #da8f08

Actionable Suggestions - 1

• tests/flytekit/unit/core/test_unions.py - 1

  • Consider more specific error message assertion · Line 160-161

Review Details

• Files reviewed - 2 · Commit Range: 8052d77..8052d77

  • flytekit/core/type_engine.py
  • tests/flytekit/unit/core/test_unions.py
• Files skipped - 0
• Tools

  • Whispers (Secret Scanner) - ✔︎ Successful
  • Detect-secrets (Secret Scanner) - ✔︎ Successful
  • MyPy (Static Code Analysis) - ✔︎ Successful
  • Astral Ruff (Static Code Analysis) - ✔︎ Successful

---

AI Code Review powered by

[flyte-bot]

Changelist by Bito

This pull request implements the following key changes.

Key Change	Files Impacted
Feature Improvement - Enhanced Union Type Error Handling	- type_engine.py - Improved error message for ambiguous union type transformations by adding potential types information - test_unions.py - Added test cases to verify enhanced error messages for ambiguous union transformations

[flyte-bot]

Consider more specific error message assertion

The error message assertion match=("Potential types:") seems too generic. Consider making it more specific to match the actual error message that would be raised when there are ambiguous union types.

Code suggestion

Check the AI-generated fix before applying

Suggested change

	match=("Potential types:")
	):
	match="Cannot determine which type to choose from Union[A, B] for value of type A. Potential types:"
	):

Code Review Run #da8f08

---

Is this a valid issue, or was it incorrectly flagged by the Agent?

• it was incorrectly flagged

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 73.22%. Comparing base (a86048a) to head (8052d77).

❗ There is a different number of reports uploaded between BASE (a86048a) and HEAD (8052d77). Click for more details.

HEAD has 7 uploads less than BASE

Flag	BASE (a86048a)	HEAD (8052d77)
	8	1

Additional details and impacted files

@@             Coverage Diff             @@
##           master    #3076       +/-   ##
===========================================
- Coverage   93.28%   73.22%   -20.07%     
===========================================
  Files          36      202      +166     
  Lines        1728    21432    +19704     
  Branches        0     2760     +2760     
===========================================
+ Hits         1612    15693    +14081     
- Misses        116     4956     +4840     
- Partials        0      783      +783     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[flyte-bot]

Code Review Agent Run #5172b2

Actionable Suggestions - 0

Review Details

• Files reviewed - 1 · Commit Range: 8052d77..b9298cd

  • tests/flytekit/unit/core/test_unions.py
• Files skipped - 0
• Tools

  • Whispers (Secret Scanner) - ✔︎ Successful
  • Detect-secrets (Secret Scanner) - ✔︎ Successful
  • MyPy (Static Code Analysis) - ✔︎ Successful
  • Astral Ruff (Static Code Analysis) - ✔︎ Successful

---

AI Code Review powered by

[thomasjpfan]

For your example:

@dataclass
class A:
    a: int

@dataclass
class B:
    a: int

what should we recommend the user to make it work?

[thomasjpfan]

Can we add more to this error message stating why they are ambiguous? Something like:

These types are structurally the same, because it's attributes have the same names and associated types.

Otherwise, it's hard to tell from the error what is wrong.