manual_flatten suggests code that does not compile

[xobs]

Lint name:

manual_flatten

I tried this code:

for server in self.servers.iter_mut() {
    if let Some(server_inner) = server {
        if server_inner.pid == target_pid {
            *server = None;
        }
    }
}

I expected to see this happen: The lint should not have been emitted. Alternately, the suggestion should have resulted in code that compiled.

Instead, this happened: The Quick fix resulted in code that did not compile.

Meta

• cargo clippy -V: clippy 0.1.54 (a178d032 2021-07-26)
• rustc -Vv:

  rustc 1.54.0 (a178d0322 2021-07-26)
  binary: rustc
  commit-hash: a178d0322ce20e33eac124758e837cbd80a6f633
  commit-date: 2021-07-26
  host: x86_64-pc-windows-msvc
  release: 1.54.0
  LLVM version: 12.0.1
  

[dswij]

Depending on what servers is, this might be related to #7514.

@xobs can you help clarify what servers is, or better provide a minimal example that we can run/test on?

[xobs]

Sure, here's a minimal example:

#[derive(Debug)]
struct Server {
    pid: u32,
}

fn main() {
    let target_pid = 1u32;
    let mut servers = [
        None,
        None,
        Some(Server { pid: 0u32 }),
        Some(Server { pid: 1u32 }),
    ];
    for server in servers.iter_mut() {
        if let Some(server_inner) = server {
            if server_inner.pid == target_pid {
                *server = None;
            }
        }
    }
    println!("Servers: {:x?}", servers);
}

Here's a link to the Playground, which also gives this recommendation: https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=265c9480c7cbb542e9dd26aca6562c2b

[dswij]

Thanks for the minimal example!

This seems to be similar to #6784, I think we can close one in favor of the other.