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, 3 deletions

diff --git a/src/libsyntax/parse/mod.rs b/src/libsyntax/parse/mod.rs
index cec9f7c2d9f..328f0e7f221 100644
--- a/src/libsyntax/parse/mod.rs
+++ b/src/libsyntax/parse/mod.rs
@@ -19,7 +19,6 @@ use parse::attr::ParserAttr;
 use parse::parser::Parser;
 
 use std::cell::RefCell;
-use std::io;
 use std::io::File;
 use std::str;
 
@@ -232,10 +231,10 @@ pub fn file_to_filemap(sess: @ParseSess, path: &Path, spanopt: Option<Span>)
             None => sess.span_diagnostic.handler().fatal(msg),
         }
     };
-    let bytes = match io::result(|| File::open(path).read_to_end()) {
+    let bytes = match File::open(path).read_to_end() {
         Ok(bytes) => bytes,
         Err(e) => {
-            err(format!("couldn't read {}: {}", path.display(), e.desc));
+            err(format!("couldn't read {}: {}", path.display(), e));
             unreachable!()
         }
     };