`format_code_in_doc_comments` formats some long line comments to block comments

[pan93412]

Meta

• rustfmt version: rustfmt 1.5.1-nightly (b44197ab 2022-09-05)
• Minimum reproducible repo: https://github.com/pan93412/rustfmt-format-code-in-doc-comments-issue-repro-220906
• rustfmt configuration:

  format_code_in_doc_comments = true

Description

After enabling format_code_in_doc_comments, rustfmt formats the following line comments to block comments – which is neither a documented nor an expected behavior.

struct TestStruct {
    position_currency: String, // Currency for position of this contract. If not null, 1 contract = 1 positionCurrency.
    pu: Option<i64>, // Previous event update sequense ("u" of previous message), -1 also means None
}

Expectation

rustfmt should not touch this.

struct TestStruct {
    position_currency: String, // Currency for position of this contract. If not null, 1 contract = 1 positionCurrency.
    pu: Option<i64>, // Previous event update sequense ("u" of previous message), -1 also means None
}

Actual Result

struct TestStruct {
    position_currency: String, /* Currency for position of this contract. If not null, 1 contract = 1 positionCurrency. */
    pu: Option<i64>, /* Previous event update sequense ("u" of previous message), -1 also means None */
}

Screenshot

Related

#3348

[ytmimi]

Confirming I can reproduce this with the latest master 38659ec.

[ytmimi]

I did some digging and It seems that block_style is being set to true in write_list

rustfmt/src/lists.rs

Lines 447 to 461 in 38659ec

	let block_style = if !formatting.ends_with_newline && last {
	true
	} else if starts_with_newline(comment) {
	false
	} else {
	comment.trim().contains('\n') || unicode_str_width(comment.trim()) > width
	};
	rewrite_comment(
	comment.trim_start(),
	block_style,
	comment_shape,
	formatting.config,
	)
	};

so when we call CommentRewrite::new from rewrite_comment_inner, we set things up to write a block comment.

rustfmt/src/comment.rs

Lines 564 to 568 in 38659ec

	let ((opener, closer, line_start), style) = if block_style {
	(
	CommentStyle::SingleBullet.to_str_tuplet(),
	CommentStyle::SingleBullet,
	)

For anyone interested in working on this I think there are two avenues to explore in order to address the issue:

1. Investigate how we might update the logic in write_list to pass block_style=false to rewrite_comment. write_list is a generic function used throughout the codebase so it might be difficult to make changes there without unintentionally breaking the behavior elsewhere.

2. Take the is_doc_comment boolean and the config.format_code_in_doc_comments() config value into account to try to move code execution into the light_rewrite_comment code path instead of the rewrite_comment_inner code path from within identify_comment.

rustfmt/src/comment.rs

Lines 368 to 382 in 38659ec

	} else if !config.normalize_comments()
	&& !config.wrap_comments()
	&& !config.format_code_in_doc_comments()
	{
	light_rewrite_comment(first_group, shape.indent, config, is_doc_comment)
	} else {
	rewrite_comment_inner(
	first_group,
	block_style,
	style,
	shape,
	config,
	is_doc_comment || style.is_doc_comment(),
	)?
	};

[pan93412]

Maybe I can help this!