regression: rustdoc interprets the * in /** */ doc comments as literal Markdown

[dalcde]

Code

I tried this code:

/**
 *     a
 */
pub fn foo() {}

When I run cargo test, I get

running 0 tests

test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s


running 1 test
test src/lib.rs - foo (line 1) ... FAILED

failures:

---- src/lib.rs - foo (line 1) stdout ----
error[E0425]: cannot find value `a` in this scope
 --> src/lib.rs:2:1
  |
3 | a
  | ^ not found in this scope

error: aborting due to previous error

For more information about this error, try `rustc --explain E0425`.
Couldn't compile the test.

failures:
    src/lib.rs - foo (line 1)

test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.41s

Oddly it doesn't fail with /** replaced by ///.

This worked on rust version 1.60.0-nightly (092e1c9d2 2022-01-09) but failed on rust version 1.60.0-nightly (1409c015b 2022-01-11)

[Alexendoo]

bisects to 89b9f7b, likely #92357

[camelid]

cc @GuillaumeGomez

[camelid]

The docs for the MCVE render with an itemized bullet at the top of the page on nightly, but not on stable. I think this is why replacing the /** with /// makes the error go away: the * is interpreted as part of the docs, so it triggers the indented text to be treated as a code block (it seems there must be preceding text to trigger the code block formatting).

[camelid]

It seems like /** */ comments are completely broken:

/**
 * Hello!
 */
pub fn foo() {}

I still don't understand how that change could've cause this though; the particular code removed was related to trimming whitespace, not asterisks. Must be a strange cross-interaction.

[GuillaumeGomez]

The /** */ comments have always been working like this. It's not supposed to contain * at the beginning of each line.

[camelid]

@GuillaumeGomez They actually haven't always been like this; this is a regression. On stable, it looks like this:

[GuillaumeGomez]

Interesting. How did we make the difference between:

/**
hello

 * list
 * list

and:

/**
* hello
*  * list
*  * list
*/

?

Do we need to have a star at each line or something?

[camelid]

I'm not sure exactly how it works, but I believe it's handled by this code (the code modified by the regressing PR, though I'm not sure how it caused the regression): https://doc.rust-lang.org/nightly/nightly-rustc/rustc_ast/util/comments/fn.beautify_doc_string.html

[GuillaumeGomez]

It's because we stopped trimming the beginning and the end of the doc comments to prevent bugs when different doc comment kinds are merged. I'm fixing it.