rust-lang / rust-lang/rustfmt

Multi-line expression after `=>` does not get braces

Open
#4,004 4 comments 4 reactions 0 assignees View on GitHub

Nobody has claimed this yet.

A-matches I-poor-formatting
Dominant language
Rust
Stars
7k
Forks
1.1k
Avg merge
2d 13h
Merged PRs (30d)
24

Description

In some cases, a multi-line expression in a match arm does not get braces, violating the spec.

This leads to code like this:

pat => fun(
    a,
    b,
    c,
    d,
)

We also don't generate code like this:

if foo { fun(
    a,
    b,
    c,
    d,
)}

so it seems odd to do that for match arms.

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 by reproducing the issue with the multi-line match-arm and conditional-expression examples in the report, then trace rustfmt's handling of expressions after =>. Done means multi-line expressions in match arms consistently receive braces, matching the cited specification and the report's conditional-expression example, with regression coverage for both cases.

Written by the indexing model from the issue text.

Assessment

Tech stack
rust
Domain
tooling
Issue type
Bug
Difficulty
3/5
Estimated time
1-2 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
45/100

Get new issues in your inbox

A short digest of beginner-friendly GitHub issues.