---

yaml
---
r: 151744
b: refs/heads/try2
c: 00f9263
h: refs/heads/master
v: v3

Author: alexcrichton

[refs]

@@ -5,7 +5,7 @@ refs/heads/snap-stage3: 78a7676898d9f80ab540c6df5d4c9ce35bb50463
 refs/heads/try: 519addf6277dbafccbb4159db4b710c37eaa2ec5
 refs/tags/release-0.1: 1f5c5126e96c79d22cb7862f75304136e204f105
 refs/heads/ndm: f3868061cd7988080c30d6d5bf352a5a5fe2460b
-refs/heads/try2: 3c06a0328a3c6824ff7578a6da46e133e9399854
+refs/heads/try2: 00f9263914da3d18c556d7ebc3941f9638721ac2
 refs/heads/dist-snap: ba4081a5a8573875fed17545846f6f6902c8ba8d
 refs/tags/release-0.2: c870d2dffb391e14efb05aa27898f1f6333a9596
 refs/tags/release-0.3: b5f0d0f648d9a6153664837026ba1be43d3e2503

branches/try2/src/libstd/io/mod.rs

@@ -964,6 +964,42 @@ pub trait Writer {
     /// decide whether their stream needs to be buffered or not.
     fn flush(&mut self) -> IoResult<()> { Ok(()) }
 
+    /// Writes a formatted string into this writer, returning any error
+    /// encountered.
+    ///
+    /// This method is primarily used to interface with the `format_args!`
+    /// macro, but it is rare that this should explicitly be called. The
+    /// `write!` macro should be favored to invoke this method instead.
+    ///
+    /// # Errors
+    ///
+    /// This function will return any I/O error reported while formatting.
+    fn write_fmt(&mut self, fmt: &fmt::Arguments) -> IoResult<()> {
+        // Create a shim which translates a Writer to a FormatWriter and saves
+        // off I/O errors. instead of discarding them
+        struct Adaptor<'a, T> {
+            inner: &'a mut T,
+            error: IoResult<()>,
+        }
+        impl<'a, T: Writer> fmt::FormatWriter for Adaptor<'a, T> {
+            fn write(&mut self, bytes: &[u8]) -> fmt::Result {
+                match self.inner.write(bytes) {
+                    Ok(()) => Ok(()),
+                    Err(e) => {
+                        self.error = Err(e);
+                        Err(fmt::WriteError)
+                    }
+                }
+            }
+        }
+
+        let mut output = Adaptor { inner: self, error: Ok(()) };
+        match fmt::write(&mut output, fmt) {
+            Ok(()) => Ok(()),
+            Err(..) => output.error
+        }
+    }
+
     /// Write a rust string into this sink.
     ///
     /// The bytes written will be the UTF-8 encoded version of the input string.