clippy::redundant_closure false positive: laziness

[projedi]

Clippy warns me about redundant closure:

warning: redundant closure found
   --> src/parser_lib.rs:291:14
    |
291 |     Box::new(move |s| pf()(s))
    |              ^^^^^^^^^^^^^^^^ help: remove closure as shown: `pf()`
    |
    = note: #[warn(clippy::redundant_closure)] on by default
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#redundant_closure

But the suggested transformation changes semantics: the original code executes pf only when the closure is executed; the suggested code executes pf immediately.

> cargo clippy -V
clippy 0.0.212 (265318db 2019-05-17)

[llogiq]

We should check if the path expr is indeed a Path. Should be simple enough.