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, 4 insertions, 5 deletions

diff --git a/src/libsyntax/ext/source_util.rs b/src/libsyntax/ext/source_util.rs
index f3f947ec00d..52010b39a54 100644
--- a/src/libsyntax/ext/source_util.rs
+++ b/src/libsyntax/ext/source_util.rs
@@ -20,7 +20,6 @@ use parse::token::get_ident_interner;
 use parse::token;
 use print::pprust;
 
-use std::io;
 use std::io::File;
 use std::rc::Rc;
 use std::str;
@@ -109,9 +108,9 @@ pub fn expand_include_str(cx: &mut ExtCtxt, sp: Span, tts: &[ast::TokenTree])
         None => return MacResult::dummy_expr()
     };
     let file = res_rel_file(cx, sp, &Path::new(file));
-    let bytes = match io::result(|| File::open(&file).read_to_end()) {
+    let bytes = match File::open(&file).read_to_end() {
         Err(e) => {
-            cx.span_err(sp, format!("couldn't read {}: {}", file.display(), e.desc));
+            cx.span_err(sp, format!("couldn't read {}: {}", file.display(), e));
             return MacResult::dummy_expr();
         }
         Ok(bytes) => bytes,
@@ -141,9 +140,9 @@ pub fn expand_include_bin(cx: &mut ExtCtxt, sp: Span, tts: &[ast::TokenTree])
         None => return MacResult::dummy_expr()
     };
     let file = res_rel_file(cx, sp, &Path::new(file));
-    match io::result(|| File::open(&file).read_to_end()) {
+    match File::open(&file).read_to_end() {
         Err(e) => {
-            cx.span_err(sp, format!("couldn't read {}: {}", file.display(), e.desc));
+            cx.span_err(sp, format!("couldn't read {}: {}", file.display(), e));
             return MacResult::dummy_expr();
         }
         Ok(bytes) => {