Require that errors are Send/Sync/'static.

Currently, they are not Sync because they contain a non-Sync trait
object. This is a breaking change.

The decision to make errors Send but not Sync was made in rust-lang-deprecated#110. We
believe that decision was a mistake, because it perpetuates a !Sync
restriction on all users even if their errors are, in fact, Sync.
Instead, users who need errors that are !Sync should use
synchronization when transforming their errors into error-chain
errors.

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "error-chain"
-version = "0.12.2" # remember to update html_root_url
+version = "0.13.0" # remember to update html_root_url
 authors = [ "Brian Anderson <banderson@mozilla.com>",
             "Paul Colomiets <paul@colomiets.name>",
             "Colin Kiegel <kiegel@gmx.de>",

src/error_chain.rs

@@ -231,7 +231,7 @@ macro_rules! impl_error_chain_processed {
 
             fn with_chain<E, K>(error: E, kind: K)
                 -> Self
-                where E: ::std::error::Error + Send + 'static,
+                where E: ::std::error::Error + Send + Sync + 'static,
                       K: Into<Self::ErrorKind>
             {
                 Self::with_chain(error, kind)
@@ -273,15 +273,15 @@ macro_rules! impl_error_chain_processed {
             /// Constructs a chained error from another error and a kind, and generates a backtrace.
             pub fn with_chain<E, K>(error: E, kind: K)
                 -> $error_name
-                where E: ::std::error::Error + Send + 'static,
+                where E: ::std::error::Error + Send + Sync + 'static,
                       K: Into<$error_kind_name>
             {
                 $error_name::with_boxed_chain(Box::new(error), kind)
             }
 
             /// Construct a chained error from another boxed error and a kind, and generates a backtrace
             #[allow(unknown_lints, bare_trait_objects)]
-            pub fn with_boxed_chain<K>(error: Box<::std::error::Error + Send>, kind: K)
+            pub fn with_boxed_chain<K>(error: Box<::std::error::Error + Send + Sync>, kind: K)
                 -> $error_name
                 where K: Into<$error_kind_name>
             {
@@ -426,7 +426,7 @@ macro_rules! impl_error_chain_processed {
                       EK: Into<$error_kind_name>;
         }
 
-        impl<T, E> $result_ext_name<T> for ::std::result::Result<T, E> where E: ::std::error::Error + Send + 'static {
+        impl<T, E> $result_ext_name<T> for ::std::result::Result<T, E> where E: ::std::error::Error + Send + Sync + 'static {
             fn chain_err<F, EK>(self, callback: F) -> ::std::result::Result<T, $error_name>
                 where F: FnOnce() -> EK,
                       EK: Into<$error_kind_name> {

src/example_generated.rs

@@ -36,3 +36,20 @@ error_chain! {
         Custom
     }
 }
+
+#[cfg(test)]
+mod test {
+
+    use super::Error;
+
+    #[test]
+    fn generated_error_meets_bounds() {
+        fn is_sync<T: Sync>() { }
+        fn is_send<T: Send>() { }
+        fn is_static<T: 'static>() { }
+        is_sync::<Error>();
+        is_send::<Error>();
+        is_static::<Error>();
+        assert!(true);
+    }
+}

src/lib.rs

@@ -551,7 +551,7 @@ mod error_chain;
 mod quick_main;
 pub use quick_main::ExitCode;
 mod backtrace;
-#[cfg(feature = "example_generated")]
+#[cfg(any(test, feature = "example_generated"))]
 pub mod example_generated;
 pub use backtrace::Backtrace;
 #[doc(hidden)]
@@ -603,10 +603,9 @@ pub trait ChainedError: error::Error + Send + 'static {
 
     /// Constructs a chained error from another error and a kind, and generates a backtrace.
     fn with_chain<E, K>(error: E, kind: K) -> Self
-    where
-        Self: Sized,
-        E: ::std::error::Error + Send + 'static,
-        K: Into<Self::ErrorKind>;
+        where Self: Sized,
+              E: ::std::error::Error + Send + Sync + 'static,
+              K: Into<Self::ErrorKind>;
 
     /// Returns the kind of the error.
     fn kind(&self) -> &Self::ErrorKind;
@@ -675,7 +674,7 @@ where
 #[allow(unknown_lints, bare_trait_objects)]
 pub struct State {
     /// Next error in the error chain.
-    pub next_error: Option<Box<error::Error + Send>>,
+    pub next_error: Option<Box<error::Error + Send + Sync>>,
     /// Backtrace for the current error.
     pub backtrace: InternalBacktrace,
 }
@@ -692,7 +691,7 @@ impl Default for State {
 impl State {
     /// Creates a new State type
     #[allow(unknown_lints, bare_trait_objects)]
-    pub fn new<CE: ChainedError>(e: Box<error::Error + Send>) -> State {
+    pub fn new<CE: ChainedError>(e: Box<error::Error + Send + Sync>) -> State {
         let backtrace = CE::extract_backtrace(&*e).unwrap_or_else(InternalBacktrace::new);
         State {
             next_error: Some(e),