unused_assignments not shown for vec overwrite - Rust 1.92.0-beta.3

[proski]

Summary

Clippy shipped with Rust 1.92.0-beta.3 doesn't report unused_assignments when a vector is initialized and then replaced with another value unconditionally.

Lint Name

unused_assignments

Reproducer

I tried this code:

fn main() {
    let mut value = b"0".to_vec();
    value = b"1".to_vec();
    println!("{:?}", value);
}

I expected to see this happen:

$ cargo +stable clippy
warning: value assigned to `value` is never read
 --> src/main.rs:2:13
  |
2 |     let mut value = b"0".to_vec();
  |             ^^^^^
  |
  = help: maybe it is overwritten before being read?
  = note: `#[warn(unused_assignments)]` (part of `#[warn(unused)]`) on by default

Instead, this happened:

$ cargo +beta clippy
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.05s

Nightly is affected too.

Version

rustc 1.92.0-beta.3 (f3f12444a 2025-11-09)
binary: rustc
commit-hash: f3f12444a017add0468f683f3a10656d29438a05
commit-date: 2025-11-09
host: x86_64-unknown-linux-gnu
release: 1.92.0-beta.3
LLVM version: 21.1.3

[profetia]

unused_assignments is not a Clippy lint, you should open it in the rustc repo

[Jarcho]

@rustbot transfer rust

[theemathas]

I added #![deny(unused_assignments)] to the top, then bisected with cargo bisect-rustc --start 1.91.1 --end f3f12444a017add0468f683f3a10656d29438a05 --regress success. The results are:

searched toolchains 408eacfb95ea19e248c0fe5e377980bc00682c1b through f435972085b697a1ece8ee6a1ac76efff8d1df7b


********************************************************************************
Regression in ff6dc928c5e33ce8e65c6911a790b9efcb5ef53a
********************************************************************************

Attempting to search unrolled perf builds
ERROR: couldn't find perf build comment

The regression is from #142390. cc @cjgillot