redundant_allocation warns about usage of Rc<Box<str>>

[liquidev]

Summary

Rc<str> is a fat pointer because str is an unsized type, so to turn it into a thin pointer either Rc<Box<str>> or Rc<String> has to be used. Clippy seems to be perfectly fine with the latter, but the former triggers a false positive.

Lint Name

redundant_allocation

Reproducer

The following code:

use std::rc::Rc;

struct S {
    s: Rc<Box<str>>,
}

Produces this warning:

warning: usage of `Rc<Box<str>>`
 --> src/lib.rs:4:8
  |
4 |     s: Rc<Box<str>>,
  |        ^^^^^^^^^^^^
  |
  = note: `#[warn(clippy::redundant_allocation)]` on by default
  = note: `Box<str>` is already on the heap, `Rc<Box<str>>` makes an extra allocation
  = help: consider using just `Rc<str>` or `Box<str>`
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#redundant_allocation

Version

rustc 1.61.0-nightly (5f4e06771 2022-03-10)
binary: rustc
commit-hash: 5f4e0677190b82e61dc507e3e72caf89da8e5e28
commit-date: 2022-03-10
host: x86_64-unknown-linux-gnu
release: 1.61.0-nightly
LLVM version: 14.0.0

Additional Labels

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