Collect the definition of the `Error` trait into `libstd` for now. This

sidesteps a coherence difficulty where `liballoc` had to prove that
`&str: !Error`, which didn't involve any local types.

1 files changed, 152 insertions, 0 deletions

diff --git a/src/libstd/error.rs b/src/libstd/error.rs
new file mode 100644
index 00000000000..150ffcdd77a
--- /dev/null
+++ b/src/libstd/error.rs
@@ -0,0 +1,152 @@
+// 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.
+
+#![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 boxed::Box;
+use convert::From;
+use fmt::{self, Debug, Display};
+use marker::Send;
+use num;
+use option::Option;
+use option::Option::None;
+use str;
+use string::{self, 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 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 }
+}
+
+#[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 + 'a> From<E> for Box<Error + Send + 'a> {
+    fn from(err: E) -> Box<Error + Send + 'a> {
+        Box::new(err)
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, 'b> From<&'b str> for Box<Error + Send + 'a> {
+    fn from(err: &'b str) -> Box<Error + Send + 'a> {
+        #[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(String::from_str(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 {
+        match *self {
+            str::Utf8Error::TooShort => "invalid utf-8: not enough bytes",
+            str::Utf8Error::InvalidByte(..) => "invalid utf-8: corrupt contents",
+        }
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl Error for num::ParseIntError {
+    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"
+    }
+}
+