Non idempotent output (comment before closing parenthesis)
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- Dominant language
- JavaScript
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Description
I found an example where running Prettier on its own output changes the output again.
Prettier 2.4.1
Playground link
--parser babel
Input:
const x = true &&
(
true || true
// X
);
Output:
const x =
true &&
(true || true);
// X
Running this output through Prettier again, with the exact same settings unexpectedly gives different output:
Output2:
const x = true && (true || true);
// X
Expected behavior:
Output and Output2 should be the same
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start with the linked Prettier Playground reproduction using the babel parser and compare the two formatting passes for the JSX example. Locate the relevant formatter behavior for comments before a closing parenthesis, then add a regression test showing that formatting the output again produces identical text. Done means the reported Input no longer produces different Output and Output2.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- javascript
- Domain
- tooling
- Issue type
- Bug
- Difficulty
- 3/5
- Estimated time
- 1-2 days
- Activity status
- Quiet
- Clarity
- Mostly clear
- Newbie friendliness
- 55/100