Detect multiple Literal members in a union

[AlexWaygood]

Fix #110

[Akuli]

Looks good! Just one nit.

[AlexWaygood]

Typeshed PR here: python/typeshed#6984

[Akuli]

Python 3.7 and 3.8 fail the CI because they don't have ast.Constant. Actually they have it, but Python just doesn't use it in the AST for whatever reason.

I added print(ast.dump(literal)) just under for literal in literals_in_union:, and here's how the AST looks:

akuli@akuli-desktop:~/flake8-pyi$ cat a.pyi
from typing import Union
from typing_extensions import Literal

x: Union[str, Literal['foo'], Literal['bar']]
akuli@akuli-desktop:~/flake8-pyi$ env37/bin/flake8 a.pyi
Index(value=Str(s='foo'))
Index(value=Str(s='bar'))
a.pyi:4:10: Y030 Multiple Literal members in a union. Combine them into one, e.g. "Literal[]".

akuli@akuli-desktop:~/flake8-pyi$ env310/bin/flake8 a.pyi
Constant(value='foo')
Constant(value='bar')
a.pyi:4:10: Y030 Multiple Literal members in a union. Combine them into one, e.g. "Literal['foo', 'bar']".

We should be prepared to handle Literals containing "literal ints, byte and unicode strings, bools, Enum values and None", according to PEP 586.

[AlexWaygood]

We should be prepared to handle Literals containing "literal ints, byte and unicode strings, bools, Enum values and None", according to PEP 586.

Ugh bytes and enums. Great.

[Akuli]

Thinking about it a bit more, I think the logic can be quite simple: if it's a Tuple, append the elts, and if it's anything else, append the object as is, regardless of whether it's ast.Constant or ast.Str.

[AlexWaygood]

Thinking about it a bit more, I think the logic can be quite simple: if it's a Tuple, append the elts, and if it's anything else, append the object as is, regardless of whether it's ast.Constant or ast.Str.

Yeah, mypy can reliably complain if a user puts in an incompatible value, we just need to handle the formatting

[Akuli]

I added one more test case, because I wasn't sure whether it would work in different Python versions. It seems to be fine though.

[AlexWaygood]

I added one more test case, because I wasn't sure whether it would work in different Python versions. It seems to be fine though.

Thanks! I was having my supper :)

[AlexWaygood]

Shall I hold off on merging until #113 is in?

[Akuli]

I think I'll merge this first and fix the conflicts in my PR then.

[JelleZijlstra]

Thanks for the quick implementation here @AlexWaygood!

[AlexWaygood]

Thanks for the quick implementation here @AlexWaygood!

Pleasure 😀