---

yaml
---
r: 105044
b: refs/heads/snap-stage3
c: 403e869
h: refs/heads/master
v: v3

Author: bors

[refs]

@@ -1,7 +1,7 @@
 ---
 refs/heads/master: 62f1d68439dcfd509eaca29887afa97f22938373
 refs/heads/snap-stage1: e33de59e47c5076a89eadeb38f4934f58a3618a6
-refs/heads/snap-stage3: 9dc357b8ed0ebc0755f7247deb8314c74e1acf80
+refs/heads/snap-stage3: 403e8695712cd9779b9cc91c61e780d3bfb8212a
 refs/heads/try: db814977d07bd798feb24f6b74c00800ef458a13
 refs/tags/release-0.1: 1f5c5126e96c79d22cb7862f75304136e204f105
 refs/heads/ndm: f3868061cd7988080c30d6d5bf352a5a5fe2460b

branches/snap-stage3/src/libstd/os.rs

@@ -740,11 +740,16 @@ pub fn last_os_error() -> ~str {
                                      buf.len() as DWORD,
                                      ptr::null());
             if res == 0 {
-                fail!("[{}] FormatMessage failure", errno());
+                // Sometimes FormatMessageW can fail e.g. system doesn't like langId,
+                let fm_err = errno();
+                return format!("OS Error {} (FormatMessageW() returned error {})", err, fm_err);
             }
 
-            str::from_utf16(str::truncate_utf16_at_nul(buf))
-                .expect("FormatMessageW returned invalid UTF-16")
+            let msg = str::from_utf16(str::truncate_utf16_at_nul(buf));
+            match msg {
+                Some(msg) => format!("OS Error {}: {}", err, msg),
+                None => format!("OS Error {} (FormatMessageW() returned invalid UTF-16)", err),
+            }
         }
     }