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, 3 insertions, 2 deletions

diff --git a/src/libstd/rt/task.rs b/src/libstd/rt/task.rs
index 7c43e64f17b..515eb93001a 100644
--- a/src/libstd/rt/task.rs
+++ b/src/libstd/rt/task.rs
@@ -119,6 +119,7 @@ impl Task {
 
             // Run the task main function, then do some cleanup.
             f.finally(|| {
+                #[allow(unused_must_use)]
                 fn close_outputs() {
                     let mut task = Local::borrow(None::<Task>);
                     let logger = task.get().logger.take();
@@ -126,8 +127,8 @@ impl Task {
                     let stdout = task.get().stdout.take();
                     drop(task);
                     drop(logger); // loggers are responsible for flushing
-                    match stdout { Some(mut w) => w.flush(), None => {} }
-                    match stderr { Some(mut w) => w.flush(), None => {} }
+                    match stdout { Some(mut w) => { w.flush(); }, None => {} }
+                    match stderr { Some(mut w) => { w.flush(); }, None => {} }
                 }
 
                 // First, flush/destroy the user stdout/logger because these