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, 2 insertions, 2 deletions

diff --git a/src/libsyntax/parse/token.rs b/src/libsyntax/parse/token.rs
index 6d2acd3d803..f1dd844fc7c 100644
--- a/src/libsyntax/parse/token.rs
+++ b/src/libsyntax/parse/token.rs
@@ -588,8 +588,8 @@ impl BytesContainer for InternedString {
 }
 
 impl fmt::Show for InternedString {
-    fn fmt(obj: &InternedString, f: &mut fmt::Formatter) {
-        write!(f.buf, "{}", obj.string.as_slice());
+    fn fmt(obj: &InternedString, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f.buf, "{}", obj.string.as_slice())
     }
 }