We stdlib now

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diff --git a/ctr-std/src/error.rs b/ctr-std/src/error.rs
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+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! Traits for working with Errors.
+//!
+//! # The `Error` trait
+//!
+//! `Error` is a trait representing the basic expectations for error values,
+//! i.e. values of type `E` in [`Result<T, E>`]. At a minimum, errors must provide
+//! a description, but they may optionally provide additional detail (via
+//! [`Display`]) and cause chain information:
+//!
+//! ```
+//! use std::fmt::Display;
+//!
+//! trait Error: Display {
+//!     fn description(&self) -> &str;
+//!
+//!     fn cause(&self) -> Option<&Error> { None }
+//! }
+//! ```
+//!
+//! The [`cause`] method is generally used when errors cross "abstraction
+//! boundaries", i.e.  when a one module must report an error that is "caused"
+//! by an error from a lower-level module. This setup makes it possible for the
+//! high-level module to provide its own errors that do not commit to any
+//! particular implementation, but also reveal some of its implementation for
+//! debugging via [`cause`] chains.
+//!
+//! [`Result<T, E>`]: ../result/enum.Result.html
+//! [`Display`]: ../fmt/trait.Display.html
+//! [`cause`]: trait.Error.html#method.cause
+
+#![stable(feature = "rust1", since = "1.0.0")]
+
+// A note about crates and the facade:
+//
+// Originally, the `Error` trait was defined in libcore, and the impls
+// were scattered about. However, coherence objected to this
+// arrangement, because to create the blanket impls for `Box` required
+// knowing that `&str: !Error`, and we have no means to deal with that
+// sort of conflict just now. Therefore, for the time being, we have
+// moved the `Error` trait into libstd. As we evolve a sol'n to the
+// coherence challenge (e.g., specialization, neg impls, etc) we can
+// reconsider what crate these items belong in.
+
+use any::TypeId;
+use cell;
+use char;
+use fmt::{self, Debug, Display};
+use mem::transmute;
+use num;
+use str;
+use string;
+
+/// Base functionality for all errors in Rust.
+#[stable(feature = "rust1", since = "1.0.0")]
+pub trait Error: Debug + Display {
+    /// A short description of the error.
+    ///
+    /// The description should only be used for a simple message.
+    /// It should not contain newlines or sentence-ending punctuation,
+    /// to facilitate embedding in larger user-facing strings.
+    /// For showing formatted error messages with more information see
+    /// [`Display`].
+    ///
+    /// [`Display`]: ../fmt/trait.Display.html
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::error::Error;
+    ///
+    /// match "xc".parse::<u32>() {
+    ///     Err(e) => {
+    ///         println!("Error: {}", e.description());
+    ///     }
+    ///     _ => println!("No error"),
+    /// }
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn description(&self) -> &str;
+
+    /// The lower-level cause of this error, if any.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::error::Error;
+    /// use std::fmt;
+    ///
+    /// #[derive(Debug)]
+    /// struct SuperError {
+    ///     side: SuperErrorSideKick,
+    /// }
+    ///
+    /// impl fmt::Display for SuperError {
+    ///     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+    ///         write!(f, "SuperError is here!")
+    ///     }
+    /// }
+    ///
+    /// impl Error for SuperError {
+    ///     fn description(&self) -> &str {
+    ///         "I'm the superhero of errors!"
+    ///     }
+    ///
+    ///     fn cause(&self) -> Option<&Error> {
+    ///         Some(&self.side)
+    ///     }
+    /// }
+    ///
+    /// #[derive(Debug)]
+    /// struct SuperErrorSideKick;
+    ///
+    /// impl fmt::Display for SuperErrorSideKick {
+    ///     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+    ///         write!(f, "SuperErrorSideKick is here!")
+    ///     }
+    /// }
+    ///
+    /// impl Error for SuperErrorSideKick {
+    ///     fn description(&self) -> &str {
+    ///         "I'm SuperError side kick!"
+    ///     }
+    /// }
+    ///
+    /// fn get_super_error() -> Result<(), SuperError> {
+    ///     Err(SuperError { side: SuperErrorSideKick })
+    /// }
+    ///
+    /// fn main() {
+    ///     match get_super_error() {
+    ///         Err(e) => {
+    ///             println!("Error: {}", e.description());
+    ///             println!("Caused by: {}", e.cause().unwrap());
+    ///         }
+    ///         _ => println!("No error"),
+    ///     }
+    /// }
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn cause(&self) -> Option<&Error> { None }
+
+    /// Get the `TypeId` of `self`
+    #[doc(hidden)]
+    #[unstable(feature = "error_type_id",
+               reason = "unclear whether to commit to this public implementation detail",
+               issue = "27745")]
+    fn type_id(&self) -> TypeId where Self: 'static {
+        TypeId::of::<Self>()
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, E: Error + 'a> From<E> for Box<Error + 'a> {
+    fn from(err: E) -> Box<Error + 'a> {
+        Box::new(err)
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, E: Error + Send + Sync + 'a> From<E> for Box<Error + Send + Sync + 'a> {
+    fn from(err: E) -> Box<Error + Send + Sync + 'a> {
+        Box::new(err)
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl From<String> for Box<Error + Send + Sync> {
+    fn from(err: String) -> Box<Error + Send + Sync> {
+        #[derive(Debug)]
+        struct StringError(String);
+
+        impl Error for StringError {
+            fn description(&self) -> &str { &self.0 }
+        }
+
+        impl Display for StringError {
+            fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+                Display::fmt(&self.0, f)
+            }
+        }
+
+        Box::new(StringError(err))
+    }
+}
+
+#[stable(feature = "string_box_error", since = "1.7.0")]
+impl From<String> for Box<Error> {
+    fn from(str_err: String) -> Box<Error> {
+        let err1: Box<Error + Send + Sync> = From::from(str_err);
+        let err2: Box<Error> = err1;
+        err2
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, 'b> From<&'b str> for Box<Error + Send + Sync + 'a> {
+    fn from(err: &'b str) -> Box<Error + Send + Sync + 'a> {
+        From::from(String::from(err))
+    }
+}
+
+#[stable(feature = "string_box_error", since = "1.7.0")]
+impl<'a> From<&'a str> for Box<Error> {
+    fn from(err: &'a str) -> Box<Error> {
+        From::from(String::from(err))
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl Error for str::ParseBoolError {
+    fn description(&self) -> &str { "failed to parse bool" }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl Error for str::Utf8Error {
+    fn description(&self) -> &str {
+        "invalid utf-8: corrupt contents"
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl Error for num::ParseIntError {
+    fn description(&self) -> &str {
+        self.__description()
+    }
+}
+
+#[unstable(feature = "try_from", issue = "33417")]
+impl Error for num::TryFromIntError {
+    fn description(&self) -> &str {
+        self.__description()
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl Error for num::ParseFloatError {
+    fn description(&self) -> &str {
+        self.__description()
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl Error for string::FromUtf8Error {
+    fn description(&self) -> &str {
+        "invalid utf-8"
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl Error for string::FromUtf16Error {
+    fn description(&self) -> &str {
+        "invalid utf-16"
+    }
+}
+
+#[stable(feature = "str_parse_error2", since = "1.8.0")]
+impl Error for string::ParseError {
+    fn description(&self) -> &str {
+        match *self {}
+    }
+}
+
+#[stable(feature = "decode_utf16", since = "1.9.0")]
+impl Error for char::DecodeUtf16Error {
+    fn description(&self) -> &str {
+        "unpaired surrogate found"
+    }
+}
+
+#[stable(feature = "box_error", since = "1.7.0")]
+impl<T: Error> Error for Box<T> {
+    fn description(&self) -> &str {
+        Error::description(&**self)
+    }
+
+    fn cause(&self) -> Option<&Error> {
+        Error::cause(&**self)
+    }
+}
+
+#[stable(feature = "fmt_error", since = "1.11.0")]
+impl Error for fmt::Error {
+    fn description(&self) -> &str {
+        "an error occurred when formatting an argument"
+    }
+}
+
+#[stable(feature = "try_borrow", since = "1.13.0")]
+impl Error for cell::BorrowError {
+    fn description(&self) -> &str {
+        "already mutably borrowed"
+    }
+}
+
+#[stable(feature = "try_borrow", since = "1.13.0")]
+impl Error for cell::BorrowMutError {
+    fn description(&self) -> &str {
+        "already borrowed"
+    }
+}
+
+#[unstable(feature = "try_from", issue = "33417")]
+impl Error for char::CharTryFromError {
+    fn description(&self) -> &str {
+        "converted integer out of range for `char`"
+    }
+}
+
+// copied from any.rs
+impl Error + 'static {
+    /// Returns true if the boxed type is the same as `T`
+    #[stable(feature = "error_downcast", since = "1.3.0")]
+    #[inline]
+    pub fn is<T: Error + 'static>(&self) -> bool {
+        // Get TypeId of the type this function is instantiated with
+        let t = TypeId::of::<T>();
+
+        // Get TypeId of the type in the trait object
+        let boxed = self.type_id();
+
+        // Compare both TypeIds on equality
+        t == boxed
+    }
+
+    /// Returns some reference to the boxed value if it is of type `T`, or
+    /// `None` if it isn't.
+    #[stable(feature = "error_downcast", since = "1.3.0")]
+    #[inline]
+    pub fn downcast_ref<T: Error + 'static>(&self) -> Option<&T> {
+        if self.is::<T>() {
+            unsafe {
+                Some(&*(self as *const Error as *const T))
+            }
+        } else {
+            None
+        }
+    }
+
+    /// Returns some mutable reference to the boxed value if it is of type `T`, or
+    /// `None` if it isn't.
+    #[stable(feature = "error_downcast", since = "1.3.0")]
+    #[inline]
+    pub fn downcast_mut<T: Error + 'static>(&mut self) -> Option<&mut T> {
+        if self.is::<T>() {
+            unsafe {
+                Some(&mut *(self as *mut Error as *mut T))
+            }
+        } else {
+            None
+        }
+    }
+}
+
+impl Error + 'static + Send {
+    /// Forwards to the method defined on the type `Any`.
+    #[stable(feature = "error_downcast", since = "1.3.0")]
+    #[inline]
+    pub fn is<T: Error + 'static>(&self) -> bool {
+        <Error + 'static>::is::<T>(self)
+    }
+
+    /// Forwards to the method defined on the type `Any`.
+    #[stable(feature = "error_downcast", since = "1.3.0")]
+    #[inline]
+    pub fn downcast_ref<T: Error + 'static>(&self) -> Option<&T> {
+        <Error + 'static>::downcast_ref::<T>(self)
+    }
+
+    /// Forwards to the method defined on the type `Any`.
+    #[stable(feature = "error_downcast", since = "1.3.0")]
+    #[inline]
+    pub fn downcast_mut<T: Error + 'static>(&mut self) -> Option<&mut T> {
+        <Error + 'static>::downcast_mut::<T>(self)
+    }
+}
+
+impl Error + 'static + Send + Sync {
+    /// Forwards to the method defined on the type `Any`.
+    #[stable(feature = "error_downcast", since = "1.3.0")]
+    #[inline]
+    pub fn is<T: Error + 'static>(&self) -> bool {
+        <Error + 'static>::is::<T>(self)
+    }
+
+    /// Forwards to the method defined on the type `Any`.
+    #[stable(feature = "error_downcast", since = "1.3.0")]
+    #[inline]
+    pub fn downcast_ref<T: Error + 'static>(&self) -> Option<&T> {
+        <Error + 'static>::downcast_ref::<T>(self)
+    }
+
+    /// Forwards to the method defined on the type `Any`.
+    #[stable(feature = "error_downcast", since = "1.3.0")]
+    #[inline]
+    pub fn downcast_mut<T: Error + 'static>(&mut self) -> Option<&mut T> {
+        <Error + 'static>::downcast_mut::<T>(self)
+    }
+}
+
+impl Error {
+    #[inline]
+    #[stable(feature = "error_downcast", since = "1.3.0")]
+    /// Attempt to downcast the box to a concrete type.
+    pub fn downcast<T: Error + 'static>(self: Box<Self>) -> Result<Box<T>, Box<Error>> {
+        if self.is::<T>() {
+            unsafe {
+                let raw: *mut Error = Box::into_raw(self);
+                Ok(Box::from_raw(raw as *mut T))
+            }
+        } else {
+            Err(self)
+        }
+    }
+}
+
+impl Error + Send {
+    #[inline]
+    #[stable(feature = "error_downcast", since = "1.3.0")]
+    /// Attempt to downcast the box to a concrete type.
+    pub fn downcast<T: Error + 'static>(self: Box<Self>)
+                                        -> Result<Box<T>, Box<Error + Send>> {
+        let err: Box<Error> = self;
+        <Error>::downcast(err).map_err(|s| unsafe {
+            // reapply the Send marker
+            transmute::<Box<Error>, Box<Error + Send>>(s)
+        })
+    }
+}
+
+impl Error + Send + Sync {
+    #[inline]
+    #[stable(feature = "error_downcast", since = "1.3.0")]
+    /// Attempt to downcast the box to a concrete type.
+    pub fn downcast<T: Error + 'static>(self: Box<Self>)
+                                        -> Result<Box<T>, Box<Self>> {
+        let err: Box<Error> = self;
+        <Error>::downcast(err).map_err(|s| unsafe {
+            // reapply the Send+Sync marker
+            transmute::<Box<Error>, Box<Error + Send + Sync>>(s)
+        })
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::Error;
+    use fmt;
+
+    #[derive(Debug, PartialEq)]
+    struct A;
+    #[derive(Debug, PartialEq)]
+    struct B;
+
+    impl fmt::Display for A {
+        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+            write!(f, "A")
+        }
+    }
+    impl fmt::Display for B {
+        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+            write!(f, "B")
+        }
+    }
+
+    impl Error for A {
+        fn description(&self) -> &str { "A-desc" }
+    }
+    impl Error for B {
+        fn description(&self) -> &str { "A-desc" }
+    }
+
+    #[test]
+    fn downcasting() {
+        let mut a = A;
+        let mut a = &mut a as &mut (Error + 'static);
+        assert_eq!(a.downcast_ref::<A>(), Some(&A));
+        assert_eq!(a.downcast_ref::<B>(), None);
+        assert_eq!(a.downcast_mut::<A>(), Some(&mut A));
+        assert_eq!(a.downcast_mut::<B>(), None);
+
+        let a: Box<Error> = Box::new(A);
+        match a.downcast::<B>() {
+            Ok(..) => panic!("expected error"),
+            Err(e) => assert_eq!(*e.downcast::<A>().unwrap(), A),
+        }
+    }
+}