fix: Support Union and Optional in DataType.infer_from_type

[srilman]

Changes Made

Noticed it when I was writing some other test, and got really annoying so I just dealt with it.

Note that the workarounds seem kind of bad, so I might take a better look at it at another point. Just a temp solution.

[srilman]

I noticed that in VSCode rendering, it is happier with + signs then - or *. All three are valid in Markdown, and others like IPython don't care. So I vote for using these.

[srilman]

Added labels so its easier to tell which one fails

[greptile-apps]

Greptile Summary

This PR adds support for Union and Optional types in DataType.infer_from_type, which previously couldn't handle these type annotations.

Implementation approach:

• Added handling for both old-style (Union[str, int]) and new-style (str | int) union syntax
• For unions where all types are the same, returns that single type
• For Optional types (str | None), returns the non-null type
• For unions with multiple distinct types, falls back to python() type
• Moved typing import to module level and added UnionType from types module

Test coverage:
Tests were added for: str | int, str | None, str | int | None, and Optional[str]. The test file was also improved by converting all test cases to use pytest.param with descriptive IDs for better test output readability.

Confidence Score: 4/5

• Safe to merge - adds Union/Optional type support with correct logic and comprehensive test coverage
• The implementation correctly handles Union and Optional types through recursive type inference. While the author notes this is a temporary solution, the logic is sound: unions with identical types return that type, Optional types (Type | None) return the non-null type, and other unions fall back to python(). Test coverage is comprehensive with clear test case naming.
• No files require special attention - all changes are straightforward and well-tested

Important Files Changed

Filename	Overview
daft/datatype.py	Adds Union and Optional type support to type inference by checking for typing.Union or UnionType, recursively inferring member types, and handling Optional (Type
tests/test_datatype_inference.py	Adds comprehensive test coverage for Union and Optional types including str

_{Last reviewed commit: 7b35a0f}

[greptile-apps]

_{3 files reviewed, no comments}

_{Edit Code Review Agent Settings | Greptile}