feature to use core::error::Error instead of std::error::Error (#154)

Cargo.toml

@@ -34,6 +34,7 @@ alloc = ["managed/alloc"]
 std = ["alloc"]
 trace-pkt = ["alloc"]
 paranoid_unsafe = []
+core_error = []
 
 # INTERNAL: enables the `__dead_code_marker!` macro.
 # used as part of the `scripts/test_dead_code_elim.sh`

README.md

@@ -120,6 +120,8 @@ When using `gdbstub` in `#![no_std]` contexts, make sure to set `default-feature
     -   Add a `TargetError::Io` variant to simplify `std::io::Error` handling from Target methods.
 -   `paranoid_unsafe`
     -   Please refer to the [`unsafe` in `gdbstub`](#unsafe-in-gdbstub) section below for more details.
+-   `core_error`
+    -   Make `GdbStubError` implement [`core::error::Error`](https://doc.rust-lang.org/core/error/trait.Error.html) instead of `std::error::Error`.
 
 ## Examples
 

src/lib.rs

@@ -27,6 +27,9 @@
 //! - `paranoid_unsafe`
 //!     - Please refer to the [`unsafe` in `gdbstub`](https://github.com/daniel5151/gdbstub#unsafe-in-gdbstub)
 //!       section of the README.md for more details.
+//! - `core_error`
+//!     - Make `GdbStubError` implement [`core::error::Error`](https://doc.rust-lang.org/core/error/trait.Error.html)
+//!       instead of `std::error::Error`.
 //!
 //! ## Getting Started
 //!

src/stub/error.rs

@@ -1,9 +1,13 @@
 use crate::protocol::PacketParseError;
 use crate::protocol::ResponseWriterError;
 use crate::util::managed_vec::CapacityError;
+#[cfg(feature = "core_error")]
+use core::error::Error as CoreError;
 use core::fmt::Debug;
 use core::fmt::Display;
 use core::fmt::{self};
+#[cfg(all(feature = "std", not(feature = "core_error")))]
+use std::error::Error as CoreError;
 
 /// An error that may occur while interacting with a
 /// [`Connection`](crate::conn::Connection).
@@ -145,8 +149,8 @@ where
     }
 }
 
-#[cfg(feature = "std")]
-impl<T, C> std::error::Error for GdbStubError<T, C>
+#[cfg(any(feature = "std", feature = "core_error"))]
+impl<T, C> CoreError for GdbStubError<T, C>
 where
     C: Debug + Display,
     T: Debug + Display,