From 1d6379e7158961a65592508086dee1a0e192b009 Mon Sep 17 00:00:00 2001
From: Victor Koenders <gpg@trangar.com>
Date: Sat, 16 Oct 2021 12:04:23 +0200
Subject: [PATCH] Added support for Cell and RefCell

---
 src/de/impls.rs      | 22 ++++++++++++++++++++++
 src/enc/impls.rs     | 35 +++++++++++++++++++++++++++++++++++
 src/error.rs         |  8 ++++++++
 tests/basic_types.rs | 23 ++++++++++++++++++++++-
 4 files changed, 87 insertions(+), 1 deletion(-)

diff --git a/src/de/impls.rs b/src/de/impls.rs
index b5b0933..fc6170d 100644
--- a/src/de/impls.rs
+++ b/src/de/impls.rs
@@ -1,3 +1,5 @@
+use core::cell::{Cell, RefCell};
+
 use super::{BorrowDecodable, BorrowDecode, Decodable, Decode};
 use crate::error::DecodeError;
 
@@ -175,6 +177,26 @@ where
     }
 }
 
+impl<'de, T> Decodable for Cell<T>
+where
+    T: Decodable,
+{
+    fn decode<D: Decode>(decoder: D) -> Result<Self, DecodeError> {
+        let t = T::decode(decoder)?;
+        Ok(Cell::new(t))
+    }
+}
+
+impl<'de, T> Decodable for RefCell<T>
+where
+    T: Decodable,
+{
+    fn decode<D: Decode>(decoder: D) -> Result<Self, DecodeError> {
+        let t = T::decode(decoder)?;
+        Ok(RefCell::new(t))
+    }
+}
+
 impl<'a, 'de, T> Decode for &'a mut T
 where
     T: Decode,
diff --git a/src/enc/impls.rs b/src/enc/impls.rs
index 7a05569..912f101 100644
--- a/src/enc/impls.rs
+++ b/src/enc/impls.rs
@@ -1,3 +1,5 @@
+use core::cell::{Cell, RefCell};
+
 use super::{Encode, Encodeable};
 use crate::error::EncodeError;
 
@@ -169,6 +171,39 @@ where
     }
 }
 
+impl<T> Encodeable for Cell<T>
+where
+    T: Encodeable + Copy,
+{
+    fn encode<E: Encode>(&self, encoder: E) -> Result<(), EncodeError> {
+        T::encode(&self.get(), encoder)
+    }
+}
+
+impl<T> Encodeable for RefCell<T>
+where
+    T: Encodeable,
+{
+    fn encode<E: Encode>(&self, encoder: E) -> Result<(), EncodeError> {
+        let borrow_guard = self
+            .try_borrow()
+            .map_err(|e| EncodeError::RefCellAlreadyBorrowed {
+                inner: e,
+                type_name: core::any::type_name::<RefCell<T>>(),
+            })?;
+        T::encode(&borrow_guard, encoder)
+    }
+}
+
+impl<'a, T> Encodeable for &'a T
+where
+    T: Encodeable,
+{
+    fn encode<E: Encode>(&self, encoder: E) -> Result<(), EncodeError> {
+        T::encode(self, encoder)
+    }
+}
+
 impl<'a, T> Encode for &'a mut T
 where
     T: Encode,
diff --git a/src/error.rs b/src/error.rs
index e687cac..e3e7969 100644
--- a/src/error.rs
+++ b/src/error.rs
@@ -7,6 +7,14 @@ pub enum EncodeError {
     /// The writer ran out of storage.
     UnexpectedEnd,
 
+    /// The RefCell<T> is already borrowed
+    RefCellAlreadyBorrowed {
+        /// The inner borrow error
+        inner: core::cell::BorrowError,
+        /// the type name of the RefCell being encoded that is currently borrowed.
+        type_name: &'static str,
+    },
+
     /// The targetted writer encountered an `std::io::Error`
     #[cfg(feature = "std")]
     Io {
diff --git a/tests/basic_types.rs b/tests/basic_types.rs
index 8e7781f..87adb15 100644
--- a/tests/basic_types.rs
+++ b/tests/basic_types.rs
@@ -1,5 +1,7 @@
 mod utils;
 
+use core::cell::Cell;
+use std::cell::RefCell;
 use utils::the_same;
 
 #[test]
@@ -63,12 +65,31 @@ fn test_numbers() {
         241, 242, 243, 244, 245, 246, 247, 248, 249, 250, 251, 252, 253, 254, 255
     ]);
 
-    // Option and Result
+    // Common types
     the_same(Option::<u32>::None);
     the_same(Option::<u32>::Some(1234));
 
     the_same(Result::<u32, u8>::Ok(1555));
     the_same(Result::<u32, u8>::Err(15));
+
+    the_same(Cell::<u32>::new(15));
+    the_same(RefCell::<u32>::new(15));
+}
+
+#[test]
+fn test_refcell_already_borrowed() {
+    let cell = RefCell::new(5u32);
+    // first get a mutable reference to the cell
+    let _mutable_guard = cell.borrow_mut();
+    // now try to encode it
+    let mut slice = [0u8; 10];
+    let result = bincode::encode_into_slice(&cell, &mut slice)
+        .expect_err("Encoding a borrowed refcell should fail");
+
+    match result {
+        bincode::error::EncodeError::RefCellAlreadyBorrowed { .. } => {} // ok
+        x => panic!("Expected a RefCellAlreadyBorrowed error, found {:?}", x),
+    }
 }
 
 #[test]