Parenthesize lambda in non-last record field on single line

[randrag]

When a record expression is collapsed to a single line, a fun lambda in a non-last field produces invalid F# because the lambda body extends to the end of the expression, swallowing subsequent fields.

This wraps such lambdas in parentheses, matching the existing approach used for tuple expressions (IsLambdaOrIfThenElse check in genExpr for ExprTupleNode).

Fixes #3246

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[github-actions]

🤖 This is an automated response from Repo Assist.

Welcome to Fantomas, @randrag! 🎉 Thank you for your first contribution — a well-documented soundness bug with a ready fix is exactly what the project needs.

Your analysis is spot on: in F#, fun extends to the end of the enclosing expression, so when a record is collapsed to a single line, the lambda body swallows subsequent fields. Wrapping the lambda in parentheses is the correct fix, and it's good to see you've matched the existing approach used for tuple expressions (IsLambdaOrIfThenElse in genExpr).

A few tips for a smooth review:

• Please verify your PR follows the Pull Request Ground Rules
• Make sure to include a dedicated test case that directly exercises this issue (a test named something like record with lambda in non-last field should be parenthesized on single line, 3246 would be great)
• The CONTRIBUTING.md has useful guidance for navigating the codebase

Looking forward to seeing this reviewed and merged!

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[nojaf]

Hi @randrag, thanks for the PR, this looks reasonable.
Ready for review or do you plan to do some more work on this?

[randrag]

Hi @nojaf, I'm happy with it as it is.

Thank you so much for Fantomas, which we have recently adopted to our solution of more than 2,000 F# files.

This was the only bug we picked up when initially reformatting them all.

Regards

Roland

[nojaf]

Hi @randrag, would it be okay if I am allowed to push to your branch?
Had one minor nit that I changed and bumped the changelog.
Would push and merge that and publish a new alpha.

I think I can't push because this is coming from an organization fork?
Anyway, will deal with it in another branch.

[nojaf]

Thank you so much for Fantomas, which we have recently adopted to our solution of more than 2,000 F# files.

Thanks for your kind words 😊!

Also cool to see that this was the only problem you had!