Remove the Copy requirement for foreign errors and show the error cau…

…se in Display

src/lib.rs

@@ -451,7 +451,12 @@ macro_rules! error_chain {
 
         impl ::std::fmt::Display for $error_name {
             fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
-                ::std::fmt::Display::fmt(&self.0, f)
+                let display_string = if let Some(ref cause) = (self.1).0 {
+                    format!("{}: {}", &self.0, cause)
+                } else {
+                    format!("{}", &self.0)
+                };
+                ::std::fmt::Display::fmt(&display_string, f)
             }
         }
 
@@ -467,7 +472,7 @@ macro_rules! error_chain {
             impl From<$foreign_link_error_path> for $error_name {
                 fn from(e: $foreign_link_error_path) -> Self {
                     $error_name(
-                        $error_kind_name::$foreign_link_variant(e),
+                        $error_kind_name::$foreign_link_variant,
                         (Some(Box::new(e)),
                          ::std::sync::Arc::new($crate::Backtrace::new())))
                 }
@@ -516,9 +521,8 @@ macro_rules! error_chain {
                 ) *
 
                 $(
-                    $foreign_link_variant(err: $foreign_link_error_path) {
+                    $foreign_link_variant {
                         description(&$foreign_link_desc)
-                        display("{}", err)
                     }
                 ) *
 

tests/tests.rs

@@ -14,7 +14,7 @@ fn smoke_test_1() {
 
         foreign_links { }
 
-        errors { }                
+        errors { }
     }
 }
 
@@ -27,7 +27,7 @@ fn smoke_test_2() {
 
         foreign_links { }
 
-        errors { }                
+        errors { }
     }
 }
 
@@ -38,7 +38,7 @@ fn smoke_test_3() {
 
         foreign_links { }
 
-        errors { }                
+        errors { }
     }
 }
 
@@ -84,7 +84,7 @@ mod foreign_link_test {
 
     // Note: foreign errors must be `pub` because they appear in the
     // signature of the public foreign_link_error_path
-    #[derive(Copy, Clone, Debug)]
+    #[derive(Debug)]
     pub struct ForeignError {}
 
     impl StdError for ForeignError {
@@ -94,6 +94,8 @@ mod foreign_link_test {
 
         fn cause(&self) -> Option<&StdError> { None }
     }
+
+    // StdError requires Display so we can depend on error types being Display
     impl fmt::Display for ForeignError {
         fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
             write!(formatter, "Foreign error display")
@@ -115,7 +117,7 @@ mod foreign_link_test {
     fn display_underlying_error() {
         let chained_error = try_foreign_error().err().unwrap();
         assert_eq!(
-            format!("{}", ForeignError{}),
+            format!("{}: {}", "some foreign error", ForeignError{}),
             format!("{}", chained_error)
         );
     }