rust-lang/rustfmt

Merge `.. .` tokens producing invalid syntax

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#7,011 opened on Aug 4, 2026

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A-closuresC-bugI-invalid-codegood first issue

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Description

Summary

Rustfmt produces syntactically valid, but not semantically equivalent to the original code, wrapping to parens.

There is two cases actually. In second case (field) rustfmt produces invalid syntax.

I tried to format this code:

See details in rust-analyzer/23004.

fn foo() {
    || 1.. .method();
    || 1.. .field;
}

From here on, this example is used without the function signature.

Expected behavior

I expected to see this happen, two possible options:

  1. no changes
  2. range wrappend in parens: 
    || (1..).method();
|| (1..).field;

Actual behavior

Instead, this happened:

(|| 1..).method(); // semantically defferent: `method()` should be "method of the range"
|| 1...field;      // invalid token: `...`

Reproduction Steps

  1. rustfmt ./file-with-foo-fn-from-summary.rs

Meta

rustfmt --version:

rustfmt 1.10.0-nightly (11177f2235 2026-08-02)

Contributor guide

Research direction
Inspect rustfmt's handling of range expressions. Trace the code path where tokens are merged, especially where `..` and `.` combine. Look for parser or visitor logic that formats method calls and field accesses on ranges. Identify why the formatter produces invalid token sequences instead of wrapping the range in parentheses.
Tech stack
rust
Domain
tooling
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.
Half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
GitRust
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
75