False negative on mem_replace_option_with_none

[and-reas-se]

Summary

I was going trough the Learning Rust with entirely too many linked lists tutorial. I have my editor set to give me warnings from clippy. In section 3.1 the tutorial has you replacing a type with an Option, and then changing a couple of of mem::replace instances with the take() method on Option. I thought to myself "huh, that's always better, that should be a lint". So I googled, and turns out it is a lint, but for some reason the lint doesn't trigger on the code in the tutorial.

Lint Name

mem_replace_option_with_none

Reproducer

This is the code from the tutorial, but with the irrelevant parts cut out:

use std::mem;

pub struct List {
    head: Option<Box<Node>>,
}

struct Node {
    #[allow(dead_code)] // to get rid of that warning since I cut the code that read from it
    next: Option<Box<Node>>,
}

impl List {
    pub fn push(&mut self) {
        let new_node = Box::new(Node {
            next: mem::replace(&mut self.head, None),
        });

        self.head = Some(new_node);
    }
}

To reproduce create a new with cargo library crate, paste into lib.rs, and run cargo clippy.
The lint is not triggered for the mem::replace on line 15.

Version

rustc 1.65.0 (897e37553 2022-11-02)
binary: rustc
commit-hash: 897e37553bba8b42751c67658967889d11ecd120
commit-date: 2022-11-02
host: x86_64-unknown-linux-gnu
release: 1.65.0
LLVM version: 15.0.0

[J-ZhengLi]

this can further simplified as:

struct T(Option<u8>);

fn main() {
    let mut t = T(Some(1));
    let test = std::mem::replace(&mut t.0, None);
    println!("{:?}", test);
}

seems like the original lint ignores member variables like t.0, self.head for some reason.

[J-ZhengLi]

@rustbot claim