unused arguments vs borrowed pointers

[jesse99]

The test case below fails to compile, apparently because the borrow checker doesn't think an unused argument is (not) used safely.

// rustc --test ignores2.rs && ./ignores2
use std;
use path::{Path};

type rsrc_loader = fn~ (path: &Path) -> result::Result<~str, ~str>;

#[test]
fn tester()
{
    let loader: rsrc_loader = |_path| {result::Ok(~"more blah")};

    let path = path::from_str("blah");
    assert loader(&path).is_ok();
}

// ignores2.rs:10:25: 10:82 error: mismatched types: expected `rsrc_loader` but found `fn~(&core::path::Path) -> core::result::Result<~str,~str>` (lifetime re_bound(br_anon(0)) does not necessarily outlive the static lifetime)
// ignores2.rs:10     let loader: rsrc_loader = |_path| {result::Ok(~"unbalanced {{curly}} {{braces}")};
//                                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

[jesse99]

Somewhat related to #3423.

[jesse99]

Does compile and run if loader is turned into a named function.

[nikomatsakis]

This is probably #2263. The fact that re_bound(re_anon(0)) appears in the error message (which should never happen, under ordinary circumstances) is a clue.

[nikomatsakis]

But I'm not sure, it's odd. I'll have to dig into this.

[jesse99]

I've also seen this error with anonymous functions that didn't have unused arguments. Worked around it by explicitly typing the anonymous function arguments taking borrowed pointers.

[catamorphism]

This compiles for me, as of d2ad028