Duplicate Errors

[reem]

Rustc sometimes recognizes and logs the same error multiple times.

Test case: https://gist.github.com/reem/78db1ad233f1c87f9ca7

rustc --test consistently logs (note the double report on the L#33 error):

lib.rs:33:5: 33:16 error: failed to find an implementation of trait core::ops::FnOnce<(uint),uint> for fn(uint) -> uint
lib.rs:33     replace_map(b, double);
              ^~~~~~~~~~~
lib.rs:33:5: 33:16 error: failed to find an implementation of trait core::ops::FnOnce<(uint),uint> for fn(uint) -> uint
lib.rs:33     replace_map(b, double);
              ^~~~~~~~~~~
lib.rs:36:5: 36:16 error: failed to find an implementation of trait core::ops::FnOnce<(uint),uint> for closure
lib.rs:36     replace_map(b, |&mut: x: uint| x * 2);
              ^~~~~~~~~~~
lib.rs:39:5: 39:16 error: failed to find an implementation of trait core::ops::FnOnce<(uint),uint> for closure
lib.rs:39     replace_map(b, |&: x: uint| x * 2);
              ^~~~~~~~~~~
error: aborting due to 4 previous errors

[treeman]

Related test case from #11382, repeating it here for clarity:

fn main() { fail!(1.2); }

Gives

<std macros>:8:9: 8:32 error: cannot determine a type for this bounded type parameter: cannot determine the type of this number; add a suffix to specify the type explicitly
<std macros>:8         ::std::rt::begin_unwind($msg, &_FILE_LINE)
                       ^~~~~~~~~~~~~~~~~~~~~~~
<std macros>:1:1: 34:2 note: in expansion of fail!
tst.rs:1:13: 1:24 note: expansion site
<std macros>:8:9: 8:32 error: cannot determine a type for this bounded type parameter: cannot determine the type of this number; add a suffix to specify the type explicitly
<std macros>:8         ::std::rt::begin_unwind($msg, &_FILE_LINE)
                       ^~~~~~~~~~~~~~~~~~~~~~~
<std macros>:1:1: 34:2 note: in expansion of fail!
tst.rs:1:13: 1:24 note: expansion site
error: aborting due to 2 previous errors