fix(semantic): do not duplicate statements in temp Vec when binding TSModuleDeclarations

[overlookmotel]

I think this was a bug, but I don't really understand the logic, so not 100% sure.

When binding a TSModuleDeclaration, references to all its statements are collected into a Vec called module_declaration_stmts:

oxc/crates/oxc_semantic/src/binder.rs

Lines 434 to 454 in 4608549

	let state = match body {
	TSModuleDeclarationBody::TSModuleBlock(block) => {
	let mut child_state = ModuleInstanceState::NonInstantiated;
	for stmt in &block.body {
	module_declaration_stmts.extend(block.body.iter());
	child_state = get_module_instance_state_for_statement(
	builder,
	stmt,
	current_node_id,
	module_declaration_stmts,
	);
	if child_state.is_instantiated() {
	break;
	}
	}
	child_state
	}
	TSModuleDeclarationBody::TSModuleDeclaration(module) => {
	get_module_instance_state(builder, module, current_node_id)
	}
	};

But module_declaration_stmts.extend(block.body.iter()) is inside the loop, meaning that all the statements are inserted over and over until a statement is found which instantiates the namespace.

e.g. this would push 25 &Statements into the Vec:

namespace X {
  type A = string;
  type B = number;
  type C = string;
  type D = number;
  interface E {}
}

The number of entries pushed to the Vec rises exponentially with the number of statements in the namespace (100 statements -> 10,000 entries pushed).

I assume this is unintentional.

Move module_declaration_stmts.extend(block.body.iter()); to before the loop.

---

Do the &Statements need to be pushed before the loop? Could it be delayed until after? That would be more performant. Though, as I said, I don't understand the logic, so I'm not sure if that'd break it.

[overlookmotel]

• fix(semantic): do not duplicate statements in temp Vec when binding TSModuleDeclarations #15724 👈 (View in Graphite)
• main

---

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[codspeed-hq]

CodSpeed Performance Report

Merging #15724 will not alter performance

_{Comparing 11-15-fix_semantic_do_not_duplicate_statements_in_temp_vec_when_binding_tsmoduledeclaration_s (99e3d41) with main (d8d4e31)¹}

Summary

✅ 37 untouched

Footnotes

1. No successful run was found on main (4608549) during the generation of this report, so d8d4e31 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

[Copilot]

Pull Request Overview

This PR fixes a performance bug where statements in TypeScript module declarations were being duplicated exponentially in a temporary Vec during the binding process.

Key Changes:

• Moved the module_declaration_stmts.extend(block.body.iter()) call outside the loop in get_module_instance_state_impl
• This prevents statements from being added repeatedly on each iteration, reducing complexity from O(n²) to O(n)

---

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[Dunqing]

Thank you, good catch, it is a bug indeed!

Do the &Statements need to be pushed before the loop? Could it be delayed until after? That would be more performant. Though, as I said, I don't understand the logic, so I'm not sure if that'd break it.

I do not remember the logic very well. I just roughly looked through the implementation again, and don't see the blocker for this

[Dunqing]

Merge activity

• Nov 17, 8:57 AM UTC: The merge label '0-merge' was detected. This PR will be added to the Graphite merge queue once it meets the requirements.
• Nov 17, 8:57 AM UTC: Dunqing added this pull request to the Graphite merge queue.
• Nov 17, 9:03 AM UTC: Merged by the Graphite merge queue.