Suggested code does not compile with or_fun_call

[jDomantas]

In some cases suggested change regarding or_fun_call lint does not compile. Here's an example:

struct Pair {
    a: u32,
    b: u32,
}

fn foo(x: u32) -> u32 { x }

fn bar(pair: &mut Pair) {
    let borrow = &mut pair.a;
    let b = None.unwrap_or(foo(pair.b));
}

pair is partially borrowed. Calling id(pair.b) is valid, because compiler can see that only field a is borrowed, so field b can be freely used. Clippy suggests to use unwrap_or_else, and move function call into a closure. However, the closure will borrow pair fully which is not possible, and the code will not compile.

[tesuji]

I believed NLL solved this.
The code after applying suggestions compiles successfully on Rust 1.42.

[jDomantas]

This specific example is only solved just because borrow is not used later, you only need to add a use after unwrap_or to make the suggestion incorrect again:

struct Pair {
    a: u32,
    b: u32,
}

fn foo(x: u32) -> u32 { x }

fn bar(pair: &mut Pair) {
    let borrow = &mut pair.a;
    let b = None.unwrap_or(foo(pair.b));
    let x = *borrow;
}

[tesuji]

I think with this RFC (https://rust-lang.github.io/rfcs/2229-capture-disjoint-fields.html) the code should be accepted and compiled.