rustdoc: Add a new lint for broken inline code

[lukas-code]

This patch adds rustdoc::unescaped_backticks, a new rustdoc lint that will detect broken inline code nodes.

The lint woks by finding stray backticks and with some heuristics tries to guess where the second backtick might be missing.

Here is how it looks:

#![warn(rustdoc::unescaped_backticks)]

/// `add(a, b) is the same as `add(b, a)`.
pub fn add(a: i32, b: i32) -> i32 { a + b }

warning: unescaped backtick
 --> src/lib.rs:3:41
  |
3 | /// `add(a, b) is the same as `add(b, a)`.
  |                                         ^
  |
help: a previous inline code might be longer than expected
  |
3 | /// `add(a, b)` is the same as `add(b, a)`.
  |               +
help: if you meant to use a literal backtick, escape it
  |
3 | /// `add(a, b) is the same as `add(b, a)\`.
  |                                         +

If we can't get proper spans, for example if the doc comment comes from a macro expansion, we print the suggestion in help messages instead. Here's a real-world example:

warning: unescaped backtick
    --> /tracing-subscriber-0.3.17/src/layer/mod.rs:1400:9
     |
1400 | /         /// Returns an optional hint of the highest [verbosity level][level] that
1401 | |         /// this `Filter` will enable.
1402 | |         ///
1403 | |         /// If this method returns a [`LevelFilter`], it will be used as a hint to
...    |
1427 | |         /// [`Interest`]: tracing_core::subscriber::Interest
1428 | |         /// [rebuild]: tracing_core::callsite::rebuild_interest_cache
     | |_____________________________________________________________________^
     |
     = help: a previous inline code might be longer than expected
              change: Therefore, if the `Filter will change the value returned by this
             to this: Therefore, if the `Filter` will change the value returned by this
     = help: if you meant to use a literal backtick, escape it
              change: [`rebuild_interest_cache`][rebuild] is called after the value of the max
             to this: [`rebuild_interest_cache\`][rebuild] is called after the value of the max

You can find more examples here.

A limitation of the current implementation is, that it cannot suggest removing misplaced backticks, for example here.

The lint is allowed by default and nightly-only for now, but without a feature gate. This is similar to how rustdoc::invalid_html_tags and rustdoc::bare_urls were handled.

[bors]

☔ The latest upstream changes (presumably #105741) made this pull request unmergeable. Please resolve the merge conflicts.

[bors]

☔ The latest upstream changes (presumably #106833) made this pull request unmergeable. Please resolve the merge conflicts.

[lukas-code]

@lcnr It looks like there is something missing at the end of this doc comment, but I can't figure out what. Can you help me out here?

rust/compiler/rustc_trait_selection/src/solve/assembly.rs

Lines 86 to 91 in 44a500c

	/// If the self type of a goal is a projection, computing the relevant candidates is difficult.
	///
	/// To deal with this, we first try to normalize the self type and add the candidates for the normalized
	/// self type to the list of candidates in case that succeeds. Note that we can't just eagerly return in
	/// this case as projections as self types add `
	fn assemble_candidates_after_normalizing_self_ty(&mut self, goal: Goal<'tcx, G>) {

[lcnr]

    /// self type to the list of candidates in case that succeeds. Note that we can't just eagerly return in
    /// this case as projections as self types can add additional candidates.

probably wanted to write

[bors]

⌛ Testing commit f5e16d5 with merge d795284384f6445b1ed810e4f039f74d88523acc...

[bors]

💔 Test failed - checks-actions

[ehuss]

@bors retry

python setuptools issue

[bors]

☔ The latest upstream changes (presumably #110643) made this pull request unmergeable. Please resolve the merge conflicts.

[GuillaumeGomez]

@bors r=GuillaumeGomez,jyn514,notriddle rollup

[bors]

📌 Commit 4f15a77 has been approved by GuillaumeGomez,jyn514,notriddle

It is now in the queue for this repository.