rust-lang/rustfmt

PreferSameLine brace_style with trailing_comma Vertical produces weird results

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#2321 opened on Dec 30, 2017

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 (3 comments) (0 reactions) (1 assignee)Rust (4,893 stars) (760 forks)batch import
I-poor-formattinggood first issueonly-with-option

Description

Upgrading rustfmt-nightly from 0.2.15 to 0.3.4 created this change:

@@ -104,8 +122,7 @@ impl FetchCommandMessages {
 
 pub trait FetchBuilderMessages
 where
-    Self: Sized,
-{
+    Self: Sized, {
     fn prepare(self) -> FetchCommandMessages;
 
     fn num(self, num: u32) -> FetchCommandMessages {

This seems like a bug, since trailing_comma = "Vertical" should not trigger if the opening brace is on the same line.

Contributor guide

Tech stack
rust
Domain
toolingdeveloper experience
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
blocked
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Rust programmingunderstanding of rustfmt configuration options
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
40
Research direction
Investigate the interaction between `brace style = "PreferSameLine"` and `trailing comma = "Vertical"` in rustfmt. The bug shows that when the opening brace is on the same line as the trait declaration, a trailing comma is incorrectly added. Examine the source code for formatting traits and functions, likely in files related to brace placement and trailing comma logic. Check if the assignee (gentoid) has any progress or comments on the issue.