babel/packages/babel-parser/test/fixtures/experimental/pipeline-operator/hack-percent-proposal-assignment-plus/options.json

{
  "plugins": [
    [
      "pipelineOperator",
      {
        "proposal": "hack",
        "topicToken": "%"
      }
    ]
  ],
  "throws": "Unexpected += after pipeline body; any += expression acting as Hack-style pipe body must be parenthesized due to its loose operator precedence. (1:11)"
}