Span for deprecation warnings for method calls is too large

[dotdash]

The warnings currently look like this:

src/racer/matchers.rs:43:23: 43:109 warning: use of deprecated item: use into_iter, #[warn(deprecated)] on by default
src/racer/matchers.rs:43     let it = it.chain(match_fn(src, blobstart, blobend, searchstr, filepath, search_type, local).move_iter());
                                               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The span includes the expression representing the object on which the method is called. That's somewhat annoying, because e.g. vim will place the cursor at the first letter of match_fn in the above example, instead of the first letter of move_iter. It also tends quite confusing, when there's a multi-line expression (e.g. one with a match in it), where the actual method call is a few lines down from where the span begins.

[ftxqxd]

I’m probably going to fix this as part of #17215.