auto merge of #11946 : alexcrichton/rust/no-io-error, r=brson

Turns out this was a little more far-reaching than I thought it was.

The first commit is the crux of this stack of commits. The `io::io_error` condition is completely removed and the `read` and `write` methods are altered to return `IoResult<T>`. This turned out to be an incredibly far-reaching change!

Overall, I'm very happy with how this turned out (in addition with the `unused_must_use` lint). I had to almost rewrite the pretty printer in `libsyntax` as well as the the formatting in `librustdoc` (as one would expect). These two modules do *tons* of I/O, and I believe that it's definitely improved.

This pull request also introduces the `if_ok!()` macro for returning-early from something that returns a result. I made quite liberal use of this in mostly the pretty printer and html renderer, and I found its usage generally quite pleasant and convenient to have. I didn't really feel like adding any other macro while I was using it, and I figured that pretty printing could be nicer, but it's nowhere near horrid today.

This may be a controversial issue closing, but I'm going to say it.

Closes #6163

1 files changed, 1 insertions, 1 deletions

diff --git a/src/libstd/path/mod.rs b/src/libstd/path/mod.rs
index 86f96a1075b..4aa4a3feab1 100644
--- a/src/libstd/path/mod.rs
+++ b/src/libstd/path/mod.rs
@@ -533,7 +533,7 @@ pub struct Display<'a, P> {
 }
 
 impl<'a, P: GenericPath> fmt::Show for Display<'a, P> {
-    fn fmt(d: &Display<P>, f: &mut fmt::Formatter) {
+    fn fmt(d: &Display<P>, f: &mut fmt::Formatter) -> fmt::Result {
         d.with_str(|s| f.pad(s))
     }
 }