Borrow check error with "unknown scope" region for callee's self parameter

[jld]

A reduced test case, which seems as if it should be valid:

fn broken(v: &r/[u8], i: uint, j: uint) -> &r/[u8] { v.view(i, j) }

The error:

src/test.rs:1:53: 1:54 error: illegal borrow: borrowed value does not live long enough
src/test.rs:1 fn broken(v: &r/[u8], i: uint, j: uint) -> &r/[u8] { v.view(i, j) }
                                                                   ^
src/test.rs:1:51: 1:67 note: borrowed pointer must be valid for the lifetime &r as defined on the block at 1:51...
src/test.rs:1 fn broken(v: &r/[u8], i: uint, j: uint) -> &r/[u8] { v.view(i, j) }
                                                                 ^~~~~~~~~~~~~~~~
note: ...but borrowed value is only valid for unknown scope: 34.  Please report a bug.
error: aborting due to previous error

[nikomatsakis]

Looks broken all right.

[graydon]

no longer ICE; it now responds to updated input:

fn broken(v: &'r [u8], i: uint, j: uint) -> &'r [u8] { v.slice(i, j) }

with:

4464.rs:1:55: 1:56 error: illegal borrow: borrowed value does not live long enough
4464.rs:1 fn broken(v: &'r [u8], i: uint, j: uint) -> &'r [u8] { v.slice(i, j) }
                                                                 ^
4464.rs:1:53: 1:70 note: borrowed pointer must be valid for the lifetime &'r  as defined on the block at 1:53...
4464.rs:1 fn broken(v: &'r [u8], i: uint, j: uint) -> &'r [u8] { v.slice(i, j) }
                                                               ^~~~~~~~~~~~~~~~~
4464.rs:1:0: 1:70 note: ...but borrowed value is only valid for the function body at 1:0
4464.rs:1 fn broken(v: &'r [u8], i: uint, j: uint) -> &'r [u8] { v.slice(i, j) }
          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
error: aborting due to previous error

This looks like a reasonable error to mem except, hm, I think probably the signature of slice isn't right? Or something. Leaving open but moving off the priority list for 0.6 (and removed ICE label)

[jld]

fn slice(&self, start: uint, end: uint) -> &'self [T];, inside impl<T> ImmutableVector<T> for &'self [T].

I think the problem is the last part: the lifetime of the pointer/length pair itself shouldn't be constrained to be equal to the lifetime of the pointed-to data like that. So impl<T, 'r> ImmutableVector<T> for &'r [T], maybe?

[nikomatsakis]

This is rather related to #5656. I'll take a look as I work.

[nikomatsakis]

I think I have the fix for this problem (inadvertently, actually).

[nikomatsakis]

Never mind, I was wrong. It seemed related to another problem that I found, but the fix for that issue doesn't seem to have fixed this test case. I'll look at this more specifically shortly.

[catamorphism]

@graydon 's code compiles now (modified to take the lifetime parameter explicitly). I'll add a test case.

[emberian]

Still needs test, updated syntax: fn broken<'r>(v: &'r [u8], i: uint, j: uint) -> &'r [u8] { v.slice(i, j) }