perf(expr-ir): Optimize ExpansionFlags.from_ir

[dangotbanned]

What type of PR is this? (check all applicable)

• 🔧 Optimization

Related issues

• Related feat(RFC): A richer Expr IR #2572 (comment)
• Child of feat(RFC): A richer Expr IR #2572

Checklist

• Code follows style guide (ruff)
• Tests added
• Documented the changes

Description

At least until switching over to (pola-rs/polars#23351), this is a simple optimization that takes advantage of defining a class hierarchy 😄

The method was originally a port of some upstream code, but skipped the pl.col(pl.DataType) and struct/field stuff which we don't use:

• https://github.com/pola-rs/polars/blob/df4d21c30c2b383b651e194f8263244f2afaeda3/crates/polars-plan/src/plans/conversion/expr_expansion.rs#L607-L660

[dangotbanned]

@FBruzzesi thought I'd ping you as this part of the code reminded me of #2836

Was curious if you saw a way to do this in fewer steps? 😏

I think the only parts that would require some digging to know are

This branch is covering 3x subclasses:

narwhals/narwhals/_plan/_expansion.py

Line 140 in 2a48aa6

elif isinstance(e, SelectorIR):

narwhals/narwhals/_plan/expressions/expr.py

Line 449 in 2a48aa6

class RootSelector(SelectorIR):

narwhals/narwhals/_plan/expressions/expr.py

Line 462 in 2a48aa6

class BinarySelector(

narwhals/narwhals/_plan/expressions/expr.py

Line 475 in 2a48aa6

class InvertSelector(SelectorIR, t.Generic[SelectorT]):

But all the others are for these guys:

narwhals/narwhals/_plan/expressions/expr.py

Lines 104 to 149 in 2a48aa6

	class _ColumnSelection(ExprIR, config=ExprIROptions.no_dispatch()):
	"""Nodes which can resolve to `Column`(s) with a `Schema`."""
	class Columns(_ColumnSelection):
	__slots__ = ("names",)
	names: Seq[str]
	def __repr__(self) -> str:
	return f"cols({list(self.names)!r})"
	class Nth(_ColumnSelection):
	__slots__ = ("index",)
	index: int
	def __repr__(self) -> str:
	return f"nth({self.index})"
	class IndexColumns(_ColumnSelection):
	__slots__ = ("indices",)
	indices: Seq[int]
	def __repr__(self) -> str:
	return f"index_columns({self.indices!r})"
	class All(_ColumnSelection):
	def __repr__(self) -> str:
	return "all()"
	class Exclude(_ColumnSelection, child=("expr",)):
	__slots__ = ("expr", "names")
	expr: ExprIR
	"""Default is `all()`."""
	names: Seq[str]
	"""Excluded names."""
	@staticmethod
	def from_names(expr: ExprIR, *names: str | t.Iterable[str]) -> Exclude:
	return Exclude(expr=expr, names=tuple(flatten_hash_safe(names)))
	def __repr__(self) -> str:
	return f"{self.expr!r}.exclude({list(self.names)!r})"