rustfmt not idempotent with a comment + or-pattern in a macro

[Nadrieril]

Describe the bug

If I start with this code and repeatedly run rustfmt, I get:

#![feature(or_patterns)]
macro_rules! t_or_f {
    () => {
        (true // some comment
        | false)
    };
}

==>>

#![feature(or_patterns)]
macro_rules! t_or_f {
    () => {
        (true // some comment
                | false)
    };
}

==>>

#![feature(or_patterns)]
macro_rules! t_or_f {
    () => {
        (true // some comment
                        | false)
    };
}

etc. After enough iterations the | false) stops moving but it's way off to the right.

This bug doesn't appear without the comment or outside a macro. Note that this macro returns a pattern, and that or-patterns are an unstable feature.

To Reproduce

This works on a fresh project without a rustfmt.toml and with both stable and nightly rustfmt.

Expected behavior

The absence of a | false) glider trying to escape from the file.

Meta

• rustfmt version: rustfmt 1.4.24-stable (eb894d5 2020-11-05) && rustfmt 1.4.29-nightly (70ce182 2020-12-04)
• From where did you install rustfmt?: rustup
• How do you run rustfmt: tried both rustfmt and cargo fmt

[davidBar-On]

The issue is caused because original code snippet is used, since currently rustfmt is not handling comments in expressions like:

        (true // some comment
        | false)

Submitted PR #4629 with a proposed solution to the extra indentation issue. Did not try to solve the comment issue, as the extra indentation is a general problem when original code snippet is used during macro body formatting.

[calebcartwright]

Closed in #4697, fix will be in the next release