PLR6201 should only apply to hashable types

[JoElfner]

Summary

Ruff version

ruff 0.12.12

Ruff settings

PLR6201 enabled

Problem

Fix safety description of PLR6201 is misleading:

Fix safety
This rule's fix is marked as unsafe, as the use of a set literal will error at runtime if the sequence contains unhashable elements (like lists or dictionaries). While Ruff will attempt to infer the hashability of the elements, it may not always be able to do so.

This reads as if only the hashability of the rhs-sequence was the problem. But in my opinion, the hashability of the lhs is more problematic in most use cases. F.i.

def foo(val: str | list[str] | dict[str, str]) -> bool:
    return val in {"a", "b", "c"}

Version

ruff 0.12.12

[ntBre]

Thanks for the report! It looks like this is already the case in the rule's implementation, so we should definitely update the docs to reflect that.

ruff/crates/ruff_linter/src/rules/pylint/rules/literal_membership.rs

Lines 73 to 75 in 00a9e65

	// If `left`, or any of the elements in `right`, are known to _not_ be hashable, return.
	if std::iter::once(compare.left.as_ref())
	.chain(elts)

[JoElfner]

thanks!