Confusing error for missing lifetime on a closure written as `<'a> |...|`

[alexcrichton]

Formerly:

missing lifetime specifier when none is needed

struct B<T>;

impl B< <'a> ||> {}

$ rustc --crate-type=lib foo.rs 
foo.rs:3:9: 3:16 error: missing lifetime specifier
foo.rs:3 impl B< <'a> ||> {}
                 ^~~~~~~
error: aborting due to previous error

The type parameter should be a self-contained type, I'm not sure why it's asking for a lifetime specifier.

New description

The error message above seems to be contradictory, since the <'a> thing is a lifetime itself, however, the problem is the environment of the closure needs a lifetime, which is written like ||:'a. It would be nice for the error message to guide people towards the correct thing.

[huonw]

The <'a> is the lifetimes of any parameters, the lifetime of the environment is specified by ||:'a.

I'll co-opt this issue for improving the error message, since it's very confusing.

[alexcrichton]

Oops, good point, thanks!

[alexcrichton]

Now that closures look a lot more like traits I think that this has basically solved itself.