Rustdoc panics at doc comments with only an line break

[91khr]

Code

/*!
*/

Meanwhile, /*! */ (any amount of spaces) and #![doc=""], #![doc="\n"], #![doc=r#"(line break)"#] can all be processed correctly; if there is anything more than just a line break (e.g. spaces before */ or after /*!), the doc comment can be processed correctly too.

Meta

rustc --version --verbose:

rustc 1.61.0-nightly (76d770ac2 2022-04-02)
binary: rustc
commit-hash: 76d770ac21d9521db6a92a48c7b3d5b2cc535941
commit-date: 2022-04-02
host: x86_64-unknown-linux-gnu
release: 1.61.0-nightly
LLVM version: 14.0.0

Error output

There is no output, the backtrace of rustdoc is:

thread 'rustc' panicked at 'index out of bounds: the len is 0 but the index is 0', compiler/rustc_ast/src/util/comments.rs:55:28
stack backtrace:
   0: rust_begin_unwind
             at /rustc/76d770ac21d9521db6a92a48c7b3d5b2cc535941/library/std/src/panicking.rs:584:5
   1: core::panicking::panic_fmt
             at /rustc/76d770ac21d9521db6a92a48c7b3d5b2cc535941/library/core/src/panicking.rs:143:14
   2: core::panicking::panic_bounds_check
             at /rustc/76d770ac21d9521db6a92a48c7b3d5b2cc535941/library/core/src/panicking.rs:84:5
   3: rustc_ast::util::comments::beautify_doc_string
   4: <unknown>
   5: <unknown>
   6: <unknown>
   7: <unknown>
   8: <unknown>
   9: <unknown>
  10: <unknown>
  11: <unknown>
  12: <unknown>
  13: <unknown>
  14: <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once
             at /rustc/76d770ac21d9521db6a92a48c7b3d5b2cc535941/library/alloc/src/boxed.rs:1861:9
  15: <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once
             at /rustc/76d770ac21d9521db6a92a48c7b3d5b2cc535941/library/alloc/src/boxed.rs:1861:9
  16: std::sys::unix::thread::Thread::new::thread_start
             at /rustc/76d770ac21d9521db6a92a48c7b3d5b2cc535941/library/std/src/sys/unix/thread.rs:108:17
  17: start_thread
  18: __clone
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

error: internal compiler error: unexpected panic

note: the compiler unexpectedly panicked. this is a bug.

note: we would appreciate a bug report: https://github.com/rust-lang/rust/issues/new?labels=C-bug%2C+I-ICE%2C+T-compiler&template=ice.md

note: rustc 1.61.0-nightly (76d770ac2 2022-04-02) running on x86_64-unknown-linux-gnu

query stack during panic:
end of query stack

[GuillaumeGomez]

I'll take a look.