Regression with `wrap_comments=true`

[rwestphal]

Hi all,

I've noticed a regression that happened between rustfmt 1.5.2-nightly (fe7454b 2023-06-19) and rustfmt 1.5.3-nightly (4651421 2023-06-20).

In my project [1], whenever I run cargo fmt, some comment lines are mangled unexpectedly. Here's the full diff: https://pastebin.com/raw/HwqgrCUz

If I disable wrap_comments=true in rustfmt.toml, the problem no longer occurs.

Interestingly, I couldn't reproduce the problem using a small demonstration program. It only happens when using rustfmt or cargo fmt in my project (which has around 75k LoC).

This is similar to #5835, but not quite the same problem.

Please let me know if you need more info to look into this.

[1] https://github.com/rwestphal/holo

[xxchan]

This looks exactly the same as #5835 Oh, it's not. . is due to numbered list, but why + is also affected 🤔️

[xxchan]

It seems #5423 also changed how unordered list works

[xxchan]

In theory your graph contains markdown lists. You can change it to table characters or wrap it in "```", which will also make hovering doc nicer.

/// ```text
/// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/// |                                                               |
/// +                                                               +
/// |                     Mandatory Parameters                      |
/// +                                                               +
/// |                                                               |
/// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/// ``` 
fn a() {}

[xxchan]

But you used comment // instead of doc comment ///. Not sure whether it's reasonable to assume // is markdown 🤔️

---

Rust style guide doesn't mention Markdown

https://doc.rust-lang.org/nightly/style-guide/index.html#comments

Rustdoc says it uses Markdown

https://doc.rust-lang.org/rustdoc/how-to-write-documentation.html?highlight=markdown#markdown

[ytmimi]

@xxchan thanks for helping to look into this and for providing a workaround for the issue.

@rwestphal Thanks for the report. Confirming I can reproduce this with rustfmt 1.6.0-nightly (a9ae7462 2023-07-19). Here's a minimal reproducible example.

input

// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// |                                                               |
// +                                                               +
// |                     Mandatory Parameters                      |
// +                                                               +
// |                                                               |
// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

output (using wrap_comments=true):

// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// |                                                               |
// + +
// |                     Mandatory Parameters                      |
// + +
// |                                                               |
// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

[xxchan]

Basically #5423 will remove all spaces after item markers (+, 1., etc.), so I cannot tell it's a bug or feature, unlike #5835 which is definitely a bug.

#5836 is somewhat similar. i.e., the style of how to format a markdown list is controversial..

[ytmimi]

But you used comment // instead of doc comment ///. Not sure whether it's reasonable to assume // is markdown 🤔️

I believe we're incorrectly calling code that goes down the doc comment rewrite path, even when we're rewriting a normal comment. #5536 should solve the issue highlighted in #5862 (comment)

On further reflection I don't think that's the case.

[ytmimi]

@xxchan Do you have any interest in workin on the? Part of me thinks that the solution might be as simple as wrapping this in a check for is_doc_comment so we don't try to parse out code blocks or lists if we're not in a doc comment.

rustfmt/src/comment.rs

Lines 806 to 813 in f89cd3c

	if let Some(stripped) = line.strip_prefix("```") {
	self.code_block_attr = Some(CodeBlockAttribute::new(stripped))
	} else if self.fmt.config.wrap_comments() {
	if let Some(ib) = ItemizedBlock::new(line) {
	self.item_block = Some(ib);
	return false;
	}
	}