transformer: multiple object rest declarators produce invalid output

[DaZuiZui]

Description

When a single variable declaration contains multiple declarators that use object rest, the ES2018 object-rest transform can remove the first rest binding and emit a moved-from declarator as {} = null.

This was originally reported through Vite: vitejs/vite#23298

Versions

Reproduced with Oxc 0.144.0, 0.145.0, and the current main branch. It is exposed by targets that require object-rest lowering, such as Safari 11 / ES2017.

Input

function merge(e, t) {
  const { a, ...x } = e, { b, ...y } = t
  return [a, x, b, y]
}

Transforming this with target: "safari11" produces no diagnostics.

Actual output

const _excluded = ["a"], _excluded2 = ["b"];
var _objectWithoutProperties = require("@oxc-project/runtime/helpers/objectWithoutProperties");
function merge(e, t) {
  const { a } = e, { b } = t, y = _objectWithoutProperties(t, _excluded2), {} = null;
  return [a, x, b, y];
}

The generated code throws while evaluating {} = null, and x is never declared.

Expected behavior

Both rest bindings should be preserved, equivalent to:

function merge(e, t) {
  const { a } = e,
    x = _objectWithoutProperties(e, ["a"]),
    { b } = t,
    y = _objectWithoutProperties(t, ["b"])
  return [a, x, b, y]
}

Root cause

transform_variable_declaration collects replacements using the declarators original indices, then applies splice from left to right. Expanding the first object-rest declarator shifts every following index, so the next splice targets the wrong declarator.

Applying the queued replacements from right to left keeps the original indices valid. A fix and regression fixture are available in #25904.

Workaround

Splitting the destructuring into separate variable declarations avoids the index shift. Disabling minification does not avoid the bug.

AI assistance

Codex assisted with reproduction and root-cause analysis. The behavior, affected transform stage, and proposed fix were verified with focused conformance tests and transformer unit tests.