Multiline comments ending in " lead to creation of line with only spaces

[C4K3]

Input

fn main() {
    /* " */
    println!("Hello, world!");
}

Output

fn main() {
    /* " */
    
    println!("Hello, world!");
}

(notice the blank line between the comment and the println, containing 4 spaces.

Expected output

Input unchanged.

Meta

• rustfmt version: rustfmt 1.4.16-stable (939e164 2020-06-11)
• From where did you install rustfmt?: rustup

[ayazhafiz]

This seems to happen iff the comment is a /* comment with exactly " as its comment.

Putting two such comments in sequence leads to another "fun" bug: https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=70c8eb3ed7416f5101dd5297cdd8c005 🙂

This is probably simple to fix since it seems to be such a specific case, but we should check if it's repro on master.

[C4K3]

It seems to be when it contains precisely one ". /* abc " */ and /* " abc */ both reproduce the issue.

[karyon]

backport was done in #4796