librustc: hint close matches on accessing nonexisting fields

[oli-obk]

structA{foo:int,car:int,barr:int}fnmain(){let a = A{foo:5,car:9,bar:42};}

now shows

main.rs:7:39:7:42 error: structure `A` has no field named `bar`
main.rs:7let a = A{foo:5,car:9,bar:42};
^~~
main.rs:7:39:7:42 help: did you mean `car`?
main.rs:7let a = A{foo:5,car:9,bar:42};
^~~
main.rs:7:39:7:42 help: did you mean `barr`?
main.rs:7let a = A{foo:5,car:9,bar:42};
^~~

same help message for accessing fields.

can't do it for functions, as they aren't iteratable. Only exact lookups are possible there.

[emberian]

Our style is to not add any whitespace for alignment.

[emberian]

Could you add some tests for this? Just a few cases in compile-fail that the messages get emitted.

[Gankra]

@oli-obk have you made all your changes? (github doesn't notify us when you just add commits, you need to ping someone when you're ready).

Regardless, needs a rebase.

[oli-obk]

not yet, as i need to rewrite some of the error reporting code, to prevent hinting field names of fields that are actually set

[flaper87]

closing for inactivity. @oli-obk let us know when you get back to this. It needs rebase so probably a new PR would be just fine.