clippy::missing_safety_doc: Comment indentation capped at three

[phi-gamma]

When scanning comments for a # Safety section, clippy only
recognizes up to three spaces for indentation. Example:

/** This safety section is not recognized.

    # Safety

    No risk, no fun.
 */
pub unsafe extern "C" fn danger_ignored(_p: *const libc::c_char) { unimplemented!(); }

/** This one is recognized.

   # Safety

   No risk, no fun.
 */
pub unsafe extern "C" fn danger_realized(_p: *const libc::c_char) { unimplemented!(); }

The first function triggers clippy::missing_safety_doc
despite the safety section being present. This is annoying
in that four spaces are required to align with the first
line of a doc comment (/** ):

$ cargo clippy -V
clippy 0.0.212

$ cargo clippy
    Checking clip-comment v0.1.0 (/src/rust-dev/playground/clip-comment)
warning: unsafe function's docs miss `# Safety` section
 --> src/main.rs:7:1
  |
7 | pub unsafe extern "C" fn danger_ignored(_p: *const libc::c_char) { unimplemented!(); }
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: `#[warn(clippy::missing_safety_doc)]` on by default
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#missing_safety_doc

    Finished dev [unoptimized + debuginfo] target(s) in 0.16s

Playpen link.

The lint can either be disabled or enabled, but not tweaked to
match the comment style. It would be preferable if a global base
indentation level for comment continuations could be specified
instead.

[Cldfire]

Just bumped into this, here's another simple repro: https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=490989da20f67791b30d3e164790fe73

pub struct Test;

impl Test {
    /**
    Test doc comment.
    
    # Safety
    
    This documents the safety requirements of the function.
    */
    pub unsafe fn test() {}
}

[jasoncarr0]

I ran into this as well with just standard doc comments using /** instead of ///
Minimal example copied verbatim (from an impl block)

    /**
     * # Safety
     */
    pub unsafe fn foo() { }