prettier / prettier/prettier

Non idempotent output (comment before closing parenthesis)

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area:comments area:idempotency lang:typescript
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

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. 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

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