parser: false "Duplicated export" when await appears in variable initializer under .js auto-detect

export var x = await + 1; produces a spurious Duplicated export 'x' error when parsed with a .js filename (sourceType auto-detection). The same source parses cleanly with .mjs or explicit sourceType: 'module'.

Reproduction

Playground link

Steps:

mkdir /tmp/oxc-repro && cd /tmp/oxc-repro
npm init -y
npm install oxc-parser

node -e "
  const { parseSync } = require('oxc-parser');
  const src = 'export var x = await + 1;';

  // ✗ .js auto-detect: false 'Duplicated export'
  const r1 = parseSync('input.js', src);
  console.log('.js auto-detect:', r1.errors.length ? 'ERROR: ' + r1.errors[0].message : 'OK');

  // ✓ .mjs: works fine
  const r2 = parseSync('input.mjs', src);
  console.log('.mjs:', r2.errors.length ? 'ERROR: ' + r2.errors[0].message : 'OK');

  // ✓ .js with explicit sourceType: works fine
  const r3 = parseSync('input.js', src, { sourceType: 'module' });
  console.log('.js + sourceType=module:', r3.errors.length ? 'ERROR: ' + r3.errors[0].message : 'OK');

  // ✓ .js with prior module syntax: works fine
  const r4 = parseSync('input.js', 'export {}; ' + src);
  console.log('.js + prior export:', r4.errors.length ? 'ERROR: ' + r4.errors[0].message : 'OK');
"

Expected output:

.js auto-detect: OK
.mjs: OK
.js + sourceType=module: OK
.js + prior export: OK

Actual output (oxc-parser 0.129.0):

.js auto-detect: ERROR: Duplicated export 'x'
.mjs: OK
.js + sourceType=module: OK
.js + prior export: OK

V8 cross-check (confirming it's valid JS):

echo 'export var x = await + 1;' > /tmp/test.js
node --check /tmp/test.js && echo "V8: OK" || echo "V8: ERROR"
# → V8: OK

echo 'export var x = await + 1;' > /tmp/test.mjs
node --check /tmp/test.mjs && echo "V8: OK" || echo "V8: ERROR"
# → V8: OK

Analysis

The bug fires when all three conditions hold:

1. .js filename (auto-detect mode, not .mjs or explicit sourceType)
2. export is the first module syntax in the file (no prior import/export)
3. await appears in the variable initializer

The AST itself is correct — the body contains a single ExportNamedDeclaration with one declarator initialized to an AwaitExpression — but the duplicate-export check fires against what appears to be a stale pre-upgrade binding. Both labels in the error codeframe point at the same x identifier.

Other await patterns also trigger the bug:

export var x = await(1);     // ✗ Duplicated export 'x'
export var x = await + 0;    // ✗ Duplicated export 'x'

Non-await initializers do not:

export var x = 1 + 1;        // ✓
export var x = void 0;       // ✓
export var x = yield + 1;    // ✓

Spec reference

ECMA-262 §16.2.3: export VariableStatement binds the declared names as exports. In module code, await is a keyword (§16.2), so await + 1 is parsed as await (+1) — a top-level AwaitExpression of the unary expression +1. The result is a single VariableDeclaration with one binding x. There is no duplicate.

Parser matrix