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, 1 deletions

diff --git a/src/libsyntax/parse/comments.rs b/src/libsyntax/parse/comments.rs
index 7165e7b404f..f65bc3ad7a3 100644
--- a/src/libsyntax/parse/comments.rs
+++ b/src/libsyntax/parse/comments.rs
@@ -350,7 +350,8 @@ pub fn gather_comments_and_literals(span_diagnostic:
                                     path: ~str,
                                     srdr: &mut io::Reader)
                                  -> (~[Comment], ~[Literal]) {
-    let src = str::from_utf8_owned(srdr.read_to_end()).unwrap();
+    let src = srdr.read_to_end().unwrap();
+    let src = str::from_utf8_owned(src).unwrap();
     let cm = CodeMap::new();
     let filemap = cm.new_filemap(path, src);
     let rdr = lexer::new_low_level_string_reader(span_diagnostic, filemap);