Generator always parenthesizes element in list comprehension

[dhruvmanila]

Yeah, this seems like a bug:

assert_round_trip!("[i*2 for i in range(5)]");
// thread 'source_code::generator::tests::tmp_test' panicked at 'assertion failed: `(left == right)`
//  left: `"[(i * 2) for i in range(5)]"`,
// right: `"[i*2 for i in range(5)]"`', crates/ruff_python_ast/src/source_code/generator.rs:1491:9
// note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
// test source_code::generator::tests::tmp_test ... FAILED

Originally posted by @dhruvmanila in #4880 (comment)

[dhruvmanila]

Omg, too much macro use in our Generator. This is a precedence issue that's probably worth opening an issue for.

This code decides whether to parenthesize an expression or not

ruff/crates/ruff_python_ast/src/source_code/generator.rs

Lines 874 to 881 in 58a79c1

	let (op, prec) = opprec!(bin, op, BoolOp, And("and", AND), Or("or", OR));
	group_if!(prec, {
	let mut first = true;
	for val in values {
	self.p_delim(&mut first, op);
	self.unparse_expr(val, prec + 1);
	}
	});

The oprec macro took me a while to understand but precedence either gets assigned the AND (33) or OR (31) precedence (the same is true for bin op, it's just that they use slightly different values for the precedence)

Now, the generator adds parentheses if the parent's precedence is higher. We use the MAX precedence for the list comprehension, which means all expressions get parenthesized

ruff/crates/ruff_python_ast/src/source_code/generator.rs

Lines 1010 to 1019 in 58a79c1

	range: _range,
	}) => {
	self.p("[");
	self.unparse_expr(elt, precedence::MAX);
	self.unparse_comp(generators);
	self.p("]");
	}
	Expr::SetComp(ast::ExprSetComp {
	elt,
	generators,

The fix requires identifying the right precedence and passing it through. A second (unrelated) refactor could be to use an enum for the precedence instead of an u8.

Originally posted by @MichaReiser in #4880 (comment)