unused_assignments lint has trouble tracking that one match guard observes assignment from another match guard. #138069
Description
I tried this code (playground):
fn pnk(x: usize) -> &'static str { let mut k1 = "k1"; let mut h1 = "h1"; match x & 3 { 3 if { k1 = "unused?"; false } => (), _ if { h1 = k1; true } => (), _ => (), } h1 } fn main() { dbg!(pnk(3)); }I expected to see this happen: No lint complaints about the assignment to k1 in the first match guard being "unused", since the assignment is subsequently observed by the second match guard.
Instead, this happened: The unused_assignments lint has a false positive on the code above:
warning: value assigned to `k1` is never read --> src/main.rs:5:16 | 5 | 3 if { k1 = "unused?"; false } => (), | ^^ | = help: maybe it is overwritten before being read? = note: `#[warn(unused_assignments)]` on by default warning: `playground` (bin "playground") generated 1 warning Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.89s Running `target/debug/playground` [src/main.rs:13:5] pnk(3) = "unused?" Meta
I'm testing on the playground, Rust stable 1.85.0