lifetime param suggestion misses an inner 'a

[pnkfelix]

Here is some playpen code: http://is.gd/0HoeAB

Within it, there is the following routine:

        fn map_inner<'a, X:'a, Y:'a>(
            f: |&X| -> Y,
            n: NodeRef<'a, X>,
            nodes: &'a TypedArena<Node<Y>>) -> NodeRef<'a, Y> {

            match n {
                None => None,
                Some(ref n) => {
                    let y = f(&n.data);
                    Some(nodes.alloc(Node {
                                        data: y,
                                        next: map_inner(f, n.next, nodes)
                                    }))
                }
            }
        }

The signature above has a bug; it omitted a lifetime on the type of nodes.

The current lifetime suggestion that rustc produces does not include that though.

The current lifetime suggestion says:

note: consider using an explicit lifetime parameter as shown: fn map_inner<'a, X: 'a,
             Y: 'a>(f: |&X| -> Y, n: NodeRef<'a, X>,
                    nodes: &'a TypedArena<Node<Y>>) -> NodeRef<'a, Y>

when I think it should be:

note: consider using an explicit lifetime parameter as shown: fn map_inner<'a, X: 'a,
             Y: 'a>(f: |&X| -> Y, n: NodeRef<'a, X>,
                    nodes: &'a TypedArena<Node<'a, Y>>) -> NodeRef<'a, Y>

(Note the additional 'ain the type ofnodes`.)

At least, after adding that, the playpen code gets further along in compilation.

(Sorry for not reducing the test case further. Hopefully I will get the chance to do so in the near future.)

[huonw]

The current suggestion seems to be identical to the code that exists? (Sometimes it doesn't give the full set of annotations immediately, and you have to adjust & recompile a few times to reach the final correct solution, but this doesn't seem to be the case here.)

[eefriedman]

This works correctly on current Rust: https://play.rust-lang.org/?gist=266c07479fc9c8d16d38&version=stable .

[alexcrichton]

Yay!