idea: Add rule for flattening nested Literals

[diceroll123]

From PEP 586, Literal[Literal[Literal[1, 2, 3], "foo"], 5, None] is equivalent to Literal[1, 2, 3, "foo", 5, None]

Currently there's no rule I know of that would unfurl/flatten a literal structure like this. Would be neat!

I came across this while fiddling with #7880.

[T-256]

++ Union and Annotated.

[charliermarsh]

Could this not be part of PYI030 itself (https://docs.astral.sh/ruff/rules/unnecessary-literal-union/)?

[T-256]

Could this not be part of PYI030 itself (https://docs.astral.sh/ruff/rules/unnecessary-literal-union/)?

As its name says that is Unnecessery union but here I think we need Unnecessery nested.
For Unnecessery union, types get joined:

field: Literal[1] | Literal[2]  # FIX: Literal[1, 2] 

For Unnecessery nested, types get unpacked:

field: Literal[1, Literal[2]]  # FIX: Literal[1, 2]

[diceroll123]

Could this not be part of PYI030 itself (docs.astral.sh/ruff/rules/unnecessary-literal-union)?

I've implemented this in as part of #7934, but of course this is strictly for literals.

[Avasam]

Could this not be part of PYI030 itself (https://docs.astral.sh/ruff/rules/unnecessary-literal-union/)?

It could. But can also be a new code. It was not implemented in flake8-pyi for the sole reason it was not deemed worth the effort for typeshed. PyCQA/flake8-pyi#425

Also note the existence of Y061 PyCQA/flake8-pyi#435
Which prefers Literal[0] | None over Literal[0, None] and is an opinionated and purely aesthetic rule (flake8-pyi doesn't need to support enforcing the second form because they are their own users at typeshed)