format_code_in_doc_comments removes parts of non-doc comments

[vmx]

Describe the bug

All this happens only with format_code_in_doc_comments=true.

A comment gets reformatted, during this reformatting the leading parts are removed.

This is triggered within enums and structs (perhaps other things, I haven't tried). The part that is removed has to follow the comment without a whitespace and start with a square opening bracket [. Everything attached to the bracket (without a whitespace) is removed.

To Reproduce

When running this minimal example with rustfmt --config format_code_in_doc_comments=true

enum Minimal {
    Example,
    //[thisisremoved thatsleft
    // canbeanything
}

The output is:

enum Minimal {
    Example,
    /* thatsleft */
    /* canbeanything */
}

Instead of an enum, the top two lines could also be replaced with a struct, leading to the same buggy behavior:

struct Minimal {
    example: Example,

Expected behavior

I would expect that the code is untouched by rustfmt.

Meta

• rustfmt version: rustfmt 1.4.18-nightly (c1e9b7b 2020-06-13)
• From where did you install rustfmt?: rustup
• How do you run rustfmt: rustfmt, but it also happens with cargo fmt

[Veetaha]

I'll add that the line comment is reformated to an ugly star-prefixed comment:

enum Foo {
    Bar,
    // a
    // b
}

   ↓ ↓ ↓ ↓ ↓ ↓

enum Foo {
    Bar,
    /* a
     * b */
}

[scampi]

The problem comes from the Custom comment variant in src/formatting/comment.rs: //[thisisremoved is considered as the opener of a custom comment, which is then removed in left_trim_comment_line:

rustfmt/src/formatting/comment.rs

Lines 977 to 982 in 9b78491

	} else if let CommentStyle::Custom(opener) = *style {
	if line.starts_with(opener) {
	(&line[opener.len()..], true)
	} else {
	(&line[opener.trim_end().len()..], false)
	}

[ytmimi]

Going to close this as it was fixed in #5091