Merge rayon-rs#637

637: #[allow(deprecated)] impl Default for Configuration r=cuviper a=cuviper

Using `#[derive(Default)]` started triggering `Configuration`'s own
deprecation message on nightly, as it has been on our compat 1.13 as
well (though stable has been fine). We can easily `#[allow(deprecated)]`
on a manual `impl` to avoid this.

Co-authored-by: Josh Stone <[email protected]>

Author: bors[bot]

rayon-core/src/lib.rs

@@ -155,7 +155,6 @@ pub struct ThreadPoolBuilder {
 ///
 /// [`ThreadPoolBuilder`]: struct.ThreadPoolBuilder.html
 #[deprecated(note = "Use `ThreadPoolBuilder`")]
-#[derive(Default)]
 pub struct Configuration {
     builder: ThreadPoolBuilder,
 }
@@ -539,6 +538,15 @@ impl fmt::Debug for ThreadPoolBuilder {
     }
 }
 
+#[allow(deprecated)]
+impl Default for Configuration {
+    fn default() -> Self {
+        Configuration {
+            builder: Default::default(),
+        }
+    }
+}
+
 #[allow(deprecated)]
 impl fmt::Debug for Configuration {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {