auto merge of #20363 : japaric/rust/moar-uc, r=nmatsakis

The the last argument of the `ItemDecorator::expand` method has changed to `Box<FnMut>`. Syntax extensions will break.

[breaking-change]

---

This PR removes pretty much all the remaining uses of boxed closures from the libraries. There are still boxed closures under the `test` directory, but I think those should be removed or replaced with unboxed closures at the same time we remove boxed closures from the language.

In a few places I had to do some contortions (see the first commit for an example) to work around issue #19596. I have marked those workarounds with FIXMEs. In the future when `&mut F where F: FnMut` implements the `FnMut` trait, we should be able to remove those workarounds. I've take care to avoid placing the workaround functions in the public API.

Since `let f = || {}` always gets type checked as a boxed closure, I have explictly annotated those closures (with e.g. `|&:| {}`) to force the compiler to type check them as unboxed closures.

Instead of removing the type aliases (like `GetCrateDataCb`), I could have replaced them with newtypes. But this seemed like overcomplicating things for little to no gain.

I think we should be able to remove the boxed closures from the languge after this PR lands. (I'm being optimistic here)

r? @alexcrichton or @aturon 
cc @nikomatsakis 

1 files changed, 2 insertions, 2 deletions

diff --git a/src/libstd/num/strconv.rs b/src/libstd/num/strconv.rs
index b1f4e5acb93..25af3bf2d53 100644
--- a/src/libstd/num/strconv.rs
+++ b/src/libstd/num/strconv.rs
@@ -321,10 +321,10 @@ pub fn float_to_str_bytes_common<T: Float>(
         // cut off the one extra digit, and depending on its value
         // round the remaining ones.
         if limit_digits && dig == digit_count {
-            let ascii2value = |chr: u8| {
+            let ascii2value = |&: chr: u8| {
                 (chr as char).to_digit(radix).unwrap()
             };
-            let value2ascii = |val: uint| {
+            let value2ascii = |&: val: uint| {
                 char::from_digit(val, radix).unwrap() as u8
             };