Applying help message emitted by `if_then_some_else_none` results in compile error

Lint name: if_then_some_else_none

I tried this code:

fn main() {
    struct Foo;

    struct Bar<'a> {
        foo: &'a mut Foo,
    }

    let mut xs = vec![Foo];
    let _a = xs
        .iter_mut()
        .filter_map(|x| if foo() { Some(Bar { foo: x }) } else { None });
}

Running clippy on the above code gives me a diagnostic that looks like:

|         .filter_map(|x| if foo() { Some(Bar { foo: x }) } else { None });
|                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= help: consider using `bool::then` like: `foo().then(|| Bar { foo: x })`

Following this help message, I updated the code to:

    let _a = xs.iter_mut().filter_map(|x| foo().then(|| Bar { foo: x }));

This doesn't compile with the following error:

error[E0373]: closure may outlive the current function, but it borrows `x`, which is owned by the current function
  --> $DIR/if_then_some_else_none.rs:126:54
   |
LL |     let _a = xs.iter_mut().filter_map(|x| foo().then(|| Bar { foo: x }));
   |                                                      ^^            - `x` is borrowed here
   |                                                      |
   |                                                      may outlive borrowed value `x`
   |
note: closure is returned here
  --> $DIR/if_then_some_else_none.rs:126:43
   |
LL |     let _a = xs.iter_mut().filter_map(|x| foo().then(|| Bar { foo: x }));
   |                                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
help: to force the closure to take ownership of `x` (and any other referenced variables), use the `move` keyword
   |
LL |     let _a = xs.iter_mut().filter_map(|x| foo().then(move || Bar { foo: x }));
   |                                                      ^^^^^^^

error: aborting due to previous error

For more information about this error, try `rustc --explain E0373`.

In this particular case, putting move keyword before the closure will work. But it seems like just putting move keyword doesn't always work; in some cases one might need to fix more code to get the code to compile. I wonder if there's a good way of displaying helpful and accurate message to the users.

Meta

I tried on the latest master 919a1a40fe4ec1118eece46b1f4c03c311ab8cda, using directly clippy's test code.

Start with the if_then_some_else_none lint and the Clippy test code containing the shown filter_map example. Check how the help suggestion is constructed and add coverage for borrowed captures; done means the suggested rewrite compiles or the diagnostic accurately accounts for cases requiring move or other changes.