compile error using `fail!` is confusing

[metajack]

This program:

pub fn main() {
    let s: &str = "foo";
    fail!(s);
}

generates this error:

<std-macros>:37:13: 37:36 error: instantiating a type parameter with an incompatible type `&str`, which does not fulfill `Send`
<std-macros>:37             ::std::rt::begin_unwind($msg, file!(), line!())
                            ^~~~~~~~~~~~~~~~~~~~~~~
<std-macros>:32:5: 42:6 note: in expansion of fail!
badfail.rs:3:5: 3:14 note: expansion site
error: aborting due to previous error

It does point you to the right place if you read it close, but I missed it myself the first few times.

[treeman]

Triage bump. Example from op now compiles correctly, this is still relevant:

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

For the duplicate errors see #16966.