allow Error::description to be used for rust below 1.42

Author: AnderEnder

build.rs

@@ -10,6 +10,10 @@ fn main() {
         println!("cargo:rustc-cfg=has_error_source");
     }
 
+    if is_min_version("1.42").unwrap_or(false) {
+        println!("cargo:rustc-cfg=has_error_description_deprecated");
+    }
+
     // So we can get the build profile for has_backtrace_depending_on_env test
     if let Ok(profile) = env::var("PROFILE") {
         println!("cargo:rustc-cfg=build={:?}", profile);

src/error_chain.rs

@@ -301,6 +301,7 @@ macro_rules! impl_error_chain_processed {
         }
 
         impl ::std::error::Error for $error_name {
+            #[cfg(not(has_error_description_deprecated))]
             fn description(&self) -> &str {
                 self.description()
             }
@@ -354,6 +355,7 @@ macro_rules! impl_error_chain_processed {
         // The ErrorKind type
         // --------------
 
+        #[cfg(not(has_error_description_deprecated))]
         impl_error_chain_kind! {
             /// The kind of an error.
             #[derive(Debug)]
@@ -378,6 +380,31 @@ macro_rules! impl_error_chain_processed {
             }
         }
 
+       #[cfg(has_error_description_deprecated)]
+       impl_error_chain_kind! {
+            /// The kind of an error.
+            #[derive(Debug)]
+            pub enum $error_kind_name {
+                $(
+                    $(#[$meta_links])*
+                    $link_variant(e: $link_kind_path) {
+                        description(e.description())
+                        display("{}", e)
+                    }
+                ) *
+
+                $(
+                    $(#[$meta_foreign_links])*
+                    $foreign_link_variant(err: $foreign_link_error_path) {
+                        description("")
+                        display("{}", err)
+                    }
+                ) *
+
+                $($error_chunks)*
+            }
+        }
+
         $(
             $(#[$meta_links])*
             impl From<$link_kind_path> for $error_kind_name {