fix: exclude for const/let in/of decl from hoisted decls

crates/rspack_plugin_javascript/src/parser_plugin/const/if_stmt.rs

@@ -81,7 +81,9 @@ pub fn get_hoisted_declarations<'ast>(
       }
       Statement::ForIn(ForInStmt { left, body, .. })
       | Statement::ForOf(ForOfStmt { left, body, .. }) => {
-        if let ForHead::VarDecl(var_decl) = left {
+        if let ForHead::VarDecl(var_decl) = left
+          && matches!(var_decl.kind, VarDeclKind::Var)
+        {
           for decl in &var_decl.decls {
             collect_declaration_from_pat(&decl.name, &mut declarations);
           }

tests/rspack-test/configCases/parsing/dead-code-elimination/index.js

@@ -111,6 +111,29 @@ it("Shouldn't eliminate hoisted function in sloppy mode", () => {
 		expect(true).toBe(false);
 	}
 });
+
+it("Shouldn't hoist const/let from dead for-of/for-in branch", () => {
+	// Bug: const/let in for-of inside if(false) was incorrectly hoisted as var,
+	// causing a duplicate declaration with any outer let/const of the same name.
+	let output = "start";
+	if (false) {
+		for (const output of [1, 2, 3]) {
+			console.log(output);
+		}
+	}
+	expect(output).toBe("start");
+});
+
+it("Shouldn't hoist const/let from dead for-in branch", () => {
+	let key = "start";
+	if (false) {
+		for (const key in { a: 1 }) {
+			console.log(key);
+		}
+	}
+	expect(key).toBe("start");
+});
+
 if (true) {
 	return;
 }