Simplify the error Registry methods a little

src/librustc_errors/registry.rs

@@ -10,12 +10,12 @@ pub struct Registry {
 
 impl Registry {
     pub fn new(long_descriptions: &[(&'static str, Option<&'static str>)]) -> Registry {
-        Registry { long_descriptions: long_descriptions.iter().cloned().collect() }
+        Registry { long_descriptions: long_descriptions.iter().copied().collect() }
     }
 
     /// This will panic if an invalid error code is passed in
     pub fn find_description(&self, code: &str) -> Option<&'static str> {
-        self.try_find_description(code).unwrap()
+        self.long_descriptions[code]
     }
     /// Returns `InvalidErrorCode` if the code requested does not exist in the
     /// registry. Otherwise, returns an `Option` where `None` means the error
@@ -24,9 +24,6 @@ impl Registry {
         &self,
         code: &str,
     ) -> Result<Option<&'static str>, InvalidErrorCode> {
-        if !self.long_descriptions.contains_key(code) {
-            return Err(InvalidErrorCode);
-        }
-        Ok(*self.long_descriptions.get(code).unwrap())
+        self.long_descriptions.get(code).copied().ok_or(InvalidErrorCode)
     }
 }