test(traverse): add an api to get the index of the current node in Vec<'a, Statements<'a>>.

[Dunqing]

Try to get the index of the current node in Vec<'a, Statements<'a>>.

[Dunqing]

• test(traverse): add an api to get the index of the current node in Vec<'a, Statements<'a>>. #6644 👈
• main

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[codspeed-hq]

CodSpeed Performance Report

Merging #6644 will degrade performances by 38.73%

_{Comparing 10-17-test_traverse_add_an_api_to_get_the_index_of_the_current_node_in_vec_a_statements_a_ (ddeb423) with main (9281234)}

Summary

❌ 5 regressions
✅ 25 untouched benchmarks

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Benchmarks breakdown

	Benchmark	main	10-17-test_traverse_add_an_api_to_get_the_index_of_the_current_node_in_vec_a_statements_a_	Change
❌	transformer[RadixUIAdoptionSection.jsx]	158 µs	164 µs	-3.7%
❌	transformer[antd.js]	50.4 ms	69.5 ms	-27.47%
❌	transformer[cal.com.tsx]	31.3 ms	36.3 ms	-13.95%
❌	transformer[checker.ts]	20.2 ms	32.3 ms	-37.48%
❌	transformer[pdf.mjs]	7.6 ms	12.4 ms	-38.73%

[overlookmotel]

Yes, agree this API would be good. But I'm afraid at present I think no way to do it without undefined behavior.

Problem is that walk_statements has a live mutable reference to the Vec<Statement>:

oxc/crates/oxc_traverse/src/generated/walk.rs

Lines 5646 to 5656 in 9281234

	pub(crate) unsafe fn walk_statements<'a, Tr: Traverse<'a>>(
	traverser: &mut Tr,
	stmts: *mut Vec<'a, Statement<'a>>,
	ctx: &mut TraverseCtx<'a>,
	) {
	traverser.enter_statements(&mut *stmts, ctx);
	for stmt in (*stmts).iter_mut() {
	walk_statement(traverser, stmt, ctx);
	}
	traverser.exit_statements(&mut *stmts, ctx);
	}

((*stmts).iter_mut() is where that &mut ref is created)

So it's illegal to get a ref &Vec<Statement> to get the Vec's start pointer, because we already hold a &mut Vec<Statement> to the same Vec. Aliasing rules violation!

But... once we take control of Vec (#6488), we can add APIs to allow iterating over the Vec while staying purely in pointer-land, without creating any &mut reference to it. And then we should be able to do this.

Maybe I can find a way to do it prior to implementing our own Vec, but it's tricky. Is there an urgent need for this in one of the transforms?

[Dunqing]

@overlookmotel check your discord DM