missing_panics_doc shouldn't warn on unreachable!

[daxpedda]

Lint name:
missing_panics_doc

I tried this code:

pub fn unreachable() {
    unreachable!("This function panics")
}

I expected to see this happen:
No warning.

As noted by @dtolnay in #1791 (comment):

I think requiring this when calling known-panicky functions is extreme. Often something is unwrapped because it is expected to never fail. That's not something you can explain to the caller. "This function panics if... the code is wrong"?

Requiring a "Panics" section if the function uses specifically panic! would be good. If it can panic, it should be documented. If it can't panic, they should have used unreachable! instead.

Instead, this happened:

Warnings:

error: docs for function which may panic missing `# Panics` section
  --> $DIR/doc_panics.rs:98:1
   |
LL | / pub fn unreachable() {
LL | |     unreachable!("This function panics")
LL | | }
   | |_^
   |
note: first possible panic found here
  --> $DIR/doc_panics.rs:99:5
   |
LL |     unreachable!("This function panics")
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)

Meta

• cargo clippy -V: clippy 0.1.51 (3682750 2021-02-02)
• rustc -Vv:

  rustc 1.51.0-nightly (368275062 2021-02-02)
  binary: rustc
  commit-hash: 368275062fb655c1f36e0398f88b15379a1f3c93
  commit-date: 2021-02-02
  host: x86_64-unknown-linux-gnu
  release: 1.51.0-nightly
  LLVM version: 11.0.1