1.99 beta crater regression with two doc comments in one line

[cyrgani]

log: https://crater-reports.s3.amazonaws.com/beta-1.99-5/1.99.0-beta.1/gh/SuperInstance.renormalization-agent/log.txt
reduction:

//! ```
//! let x = 0; //! assert!(true);
//! ```

Bisection points to #159966. This used to compile in 1.98 (and the second part was ignored entirely), but became an error in 1.99.

[theemathas]

I don't see any PR in that rollup that seems relevant...

[apiraino]

I'vre tried running a cargo test bisection, unsure if the result is correct because the regression I see is different from the one reported here. Is this issue about something else?

Details

test result: ok. 34 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s

   Doc-tests renormalization_agent

running 1 test
test src/lib.rs - (line 32) ... error: expected item, found keyword `let`
  --> src/lib.rs:35:1
   |
35 | let ticks: Vec<f64> = (0..1024).map(|i| (i as f64 * 0.1).sin()).collect();
   | ^^^
   | |
   | `let` cannot be used for global variables
   | help: consider using `static` or `const` instead of `let`
   |
   = note: for a full list of items that can appear in modules, see <https://doc.rust-lang.org/reference/items.html>

error: aborting due to 1 previous error

Couldn't compile the test.FAILED

failures:

failures:
    src/lib.rs - (line 32)

test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.02s

searched nightlies: from nightly-2026-07-05 to nightly-2026-09-02
regressed nightly: nightly-2026-07-28
searched commit range: dc3f851...09ee43b
regressed commit: dfbea5b

bisected with cargo-bisect-rustc v0.6.11

Host triple: x86_64-unknown-linux-gnu
Reproduce with:

cargo bisect-rustc --preserve --start 1.98.0 -- test 

[cyrgani]

This is the exact same regression as what I posted above. The relevant code part is

//! ```
//! use renormalization_agent::AgentScaleMap;
//!
//! let ticks: Vec<f64> = (0..1024).map(|i| (i as f64 * 0.1).sin()).collect();
//! let mut map = AgentScaleMap::new(ticks);
//! map.extract_mean("mean");
//! map.coarse_grain(4).unwrap();
//! map.extract_mean("mean");
//!
//! let obs = map.observables.iter().find(|o| o.name == "mean").unwrap();//! assert_eq!(obs.values.len(), 2); // one per scale
//! ```

and in both this and the reduction above there is a line with two doc comments, which now causes a parser error, but was accepted in 1.98.