Stabilize the Error trait

This small commit stabilizes the `Error` trait as-is, except that `Send`
and `Debug` are added as constraints. The `Send` constraint is because
most uses of `Error` will be for trait objects, and by default we would
like these objects to be transferrable between threads. The `Debug`
constraint is to ensure that e.g. `Box<Error>` is `Debug`, and because
types that implement `Display` should certainly implement `Debug` in any case.

In the near future we expect to add `Any`-like downcasting features to
`Error`, but this is waiting on some additional
mechanisms (`Reflect`). It will be added before 1.0 via default methods.

[breaking-change]

1 files changed, 10 insertions, 5 deletions

diff --git a/src/libcore/error.rs b/src/libcore/error.rs
index 161f6c78921..d29964d63a5 100644
--- a/src/libcore/error.rs
+++ b/src/libcore/error.rs
@@ -82,16 +82,21 @@
 #![stable(feature = "rust1", since = "1.0.0")]
 
 use prelude::*;
-use fmt::Display;
+use fmt::{Debug, Display};
 
 /// Base functionality for all errors in Rust.
-#[unstable(feature = "core",
-           reason = "the exact API of this trait may change")]
-pub trait Error: Display {
-    /// A short description of the error; usually a static string.
+#[stable(feature = "rust1", since = "1.0.0")]
+pub trait Error: Debug + Display + Send {
+    /// A short description of the error.
+    ///
+    /// The description should not contain newlines or sentence-ending
+    /// punctuation, to facilitate embedding in larger user-facing
+    /// strings.
+    #[stable(feature = "rust1", since = "1.0.0")]
     fn description(&self) -> &str;
 
     /// The lower-level cause of this error, if any.
+    #[stable(feature = "rust1", since = "1.0.0")]
     fn cause(&self) -> Option<&Error> { None }
 }