Rustdoc does not format ASCII art containing `###` at the start of a line correctly

[rjvdw]

I tried this code:

//! This is some documentation with ASCII art:
//!
//! ```text
//! #..#.####.#....#.....##..
//! #..#.#....#....#....#..#.
//! ####.###..#....#....#..#.
//! #..#.#....#....#....#..#.
//! #..#.#....#....#....#..#.
//! #..#.####.####.####..##..
//! ```

I expected to see this happen: When I run rustdoc, I expect to see ASCII art in the output that matches the above example.

Instead, this happened: In the output, this actually appears:

#..#.####.#....#.....##..
#..#.#....#....#....#..#.
###.###..#....#....#..#.
#..#.#....#....#....#..#.
#..#.#....#....#....#..#.
#..#.####.####.####..##..

It appears that if a line starts with at least three #s, one gets "swallowed" somehow.

Meta

rustc --version --verbose:

rustc 1.65.0 (897e37553 2022-11-02)
binary: rustc
commit-hash: 897e37553bba8b42751c67658967889d11ecd120
commit-date: 2022-11-02
host: x86_64-apple-darwin
release: 1.65.0
LLVM version: 15.0.0

Backtrace

n/a

[GuillaumeGomez]

It's because of how # are handled for rust code blocks. I'll send a PR but we need to ensure that people are not relying on # to hide a line for non-rust code blocks.

[camelid]

This is actually a regression. I haven't bisected, but it occurred sometime between 1.50.0 and 1.63.0 based on a quick test. In 1.50.0, the following code block

/// ```markdown
/// # Header
/// ```

rendered as # Header, but in 1.63.0 it renders as a blank code block.

[GuillaumeGomez]

Thanks for the information @camelid !

[albertlarsan68]

The regression is in nightly-2021-07-15

Commits in range:

commit[0] 2021-07-13UTC: Auto merge of #86827 - camsteffen:hash-lint-resolved, r=oli-obk
commit[1] 2021-07-13UTC: Auto merge of #87044 - cjgillot:expnhash, r=petrochenkov
commit[2] 2021-07-14UTC: Auto merge of #87106 - Mark-Simulacrum:edition-no-clone, r=petrochenkov
commit[3] 2021-07-14UTC: Auto merge of #86211 - tlyu:option-result-overviews, r=joshtriplett
commit[4] 2021-07-14UTC: Auto merge of #87118 - JohnTitor:rollup-8ltidsq, r=JohnTitor
commit[5] 2021-07-14UTC: Auto merge of #87082 - michaelwoerister:const-in-debuginfo-type-names-fix, r=oli-obk,wesleywiser
commit[6] 2021-07-14UTC: Auto merge of #87133 - GuillaumeGomez:rollup-pfz9jbk, r=GuillaumeGomez
commit[7] 2021-07-14UTC: Auto merge of #86765 - cuviper:fuse-less-specialized, r=joshtriplett

Maybe this happened in #87056 (merged by #87133) (cc @GuillaumeGomez)