#28669 caused regression compiling pinyin crate on nightly

[eefriedman]

See https://tools.taskcluster.net/task-inspector/#UFk2m1UJRweSxQNABRB84w/0 ; I've confirmed the issue locally, although I haven't managed to reduce it.

For reference, the error message:

   Compiling pinyin v0.0.4 (file:///home/crate)                                                                         
src/lib.rs:157:24: 157:29 error: cannot infer an appropriate lifetime for lifetime parameter `'t` due to conflicting req
uirements [E0495]                                                                                                       
src/lib.rs:157         let cap = caps.at(0).unwrap();                                                                   
                                      ^~~~~                                                                             
src/lib.rs:157:19: 157:29 note: first, the lifetime cannot outlive the method call at 157:18...                         
src/lib.rs:157         let cap = caps.at(0).unwrap();                                                                   
                                 ^~~~~~~~~~                                                                             
src/lib.rs:157:19: 157:29 note: ...so that a type/lifetime parameter is in scope here                                   
src/lib.rs:157         let cap = caps.at(0).unwrap();                                                                   
                                 ^~~~~~~~~~                                                                             
src/lib.rs:157:19: 157:38 note: but, the lifetime must be valid for the method call at 157:18...                        
src/lib.rs:157         let cap = caps.at(0).unwrap();                                                                   
                                 ^~~~~~~~~~~~~~~~~~~                                                                    
src/lib.rs:157:19: 157:29 note: ...so that method receiver is valid for the method call                                 
src/lib.rs:157         let cap = caps.at(0).unwrap();                                                                   
                                 ^~~~~~~~~~                                                                             
error: aborting due to previous error                                                                                   
Could not compile `pinyin`.                                                                                             

To learn more, run the command again with --verbose.                                                                    
[taskcluster] Unsuccessful task run with exit code: 101 completed in 40.243 seconds                                     

CC @arielb1 .

[jonas-schievink]

Interesting, I'm wondering if I was hit by the same regression: https://travis-ci.org/jonas-schievink/lea/builds/83592818 (code in question)

(The code is horrible, so I might have been accidentally abusing a soundness bug there)

[eefriedman]

@jonas-schievink I think that's a different issue? Anyway, filed #28854 to track it.

[alexcrichton]

At least relatively minimized:

trait Borrow<T: ?Sized> {}                                       
impl<T: ?Sized> Borrow<T> for T {}                               
impl<'a, T: ?Sized> Borrow<T> for &'a T {}                       

struct Map<K: 'static>(K);                                       
static MAP: Map<&'static str> = Map("bar");                      
impl<K> Map<K> {                                                 
    fn get<T>(&self, _key: &T) -> Option<&K> where K: Borrow<T> {
        loop {}                                                  
    }                                                            
}                                                                

fn _foo<T: FnMut(&Captures)>(_: T) {}                            

struct Captures<'t>(&'t str);                                    
impl<'t> Captures<'t> {                                          
    fn at(&self) -> &'t str { loop {} }                          
}                                                                

pub fn foo() {                                                   
    _foo(|caps| {                                                
        MAP.get(&caps.at());                                     
    })                                                           
}                                                                
fn main() {}

Nominating as this code compiles on stable/beta and does not compile on nightly. Also tagging with T-compiler, but T-lang may also be appropriate.

[alexcrichton]

triage: I-nominated

[nikomatsakis]

triage: P-high

[arielb1]

this is a duplicate of #28854.