Move description of the Error trait to its own doc-comment

… rather than the module’s.

Author: SimonSapin

src/libstd/error.rs

@@ -9,34 +9,6 @@
 // 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")]
 
@@ -63,7 +35,31 @@ use num;
 use str;
 use string;
 
-/// Base functionality for all errors in Rust.
+/// `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")]
 pub trait Error: Debug + Display {
     /// A short description of the error.