False positive for redundant_closure_call when called in a closure

[Systemcluster]

Minimal example:

fn fun<T: 'static + FnMut()>(mut f: T) {
    f();
}

fn main() {
    let mut x;
    let create = || 2 * 2;
    x = create();

    fun(move || {
        println!("using x here {}", x);
        x = create();
        println!("to avoid non-relevant warnings {}", x);
    })
}

create is called in two spots, but on the first x = create(); a warning: closure called just once immediately after it was declared is emitted.

Interestingly, the warning is not emitted when any statement is between the definitian and the first usage of the closure:

let create = || 2 * 2;
println!("no warning emitted with this line");
x = create();

Meta

• cargo clippy -V: clippy 0.0.212 (9b88e0a86 2020-08-15)
• rustc -Vv:

  rustc 1.47.0-nightly (9b88e0a86 2020-08-15)
  binary: rustc
  commit-hash: 9b88e0a8667040452a94fda8548f0f5f0f801f90
  commit-date: 2020-08-15
  host: x86_64-pc-windows-msvc
  release: 1.47.0-nightly
  LLVM version: 10.0
  

[flip1995]

This lint is probably implemented with a visitor. The fix is easy: The nested_visit_map method should at least return NestedVisitorMap::OnlyBodies

[giraffate]

I will prepare a fix.